diff --git a/.eslintrc.js b/.eslintrc.js
index 9d2e19f64c..c3d03a4f68 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -28,17 +28,21 @@ module.exports = {
   rules: {
     // Following checks are temporarily disabled. We shall incrementally enable them in the
     // future, fixing any violations as we go.
-    "@typescript-eslint/no-explicit-any": 0,
-    "@typescript-eslint/no-use-before-define": 0,
-    "@typescript-eslint/explicit-function-return-type": 0,
-    "@typescript-eslint/camelcase": 0,
-    "@typescript-eslint/no-non-null-assertion": 0,
-    "@typescript-eslint/no-var-requires": 0,
-    "@typescript-eslint/ban-types": 0,
-    "no-useless-escape": 0,
-    "no-prototype-builtins": 0,
+    '@typescript-eslint/no-non-null-assertion': 0,
+
+    // Disabled checks
+    '@typescript-eslint/no-explicit-any': 0,
+    '@typescript-eslint/no-use-before-define': 0,
 
     // Required checks
-    "indent": ["error", 2]
+    'indent': ['error', 2],
+    '@typescript-eslint/explicit-function-return-type': [
+      'error',
+      {
+        'allowExpressions': true,
+        'allowTypedFunctionExpressions': true,
+        'allowHigherOrderFunctions': true
+      }
+    ],
   }
 };
diff --git a/src/auth/action-code-settings-builder.ts b/src/auth/action-code-settings-builder.ts
index 3b1441e3fe..159e78af48 100644
--- a/src/auth/action-code-settings-builder.ts
+++ b/src/auth/action-code-settings-builder.ts
@@ -169,7 +169,7 @@ export class ActionCodeSettingsBuilder {
     };
     // Remove all null and undefined fields from request.
     for (const key in request) {
-      if (request.hasOwnProperty(key)) {
+      if (Object.prototype.hasOwnProperty.call(request, key)) {
         if (typeof request[key] === 'undefined' || request[key] === null) {
           delete request[key];
         }
diff --git a/src/auth/auth-api-request.ts b/src/auth/auth-api-request.ts
index 847cda75ff..8b3d521e31 100755
--- a/src/auth/auth-api-request.ts
+++ b/src/auth/auth-api-request.ts
@@ -187,7 +187,7 @@ class TenantAwareAuthResourceUrlBuilder extends AuthResourceUrlBuilder {
  *
  * @param {any} request The providerUserInfo request object.
  */
-function validateProviderUserInfo(request: any) {
+function validateProviderUserInfo(request: any): void {
   const validKeys = {
     rawId: true,
     providerId: true,
@@ -247,7 +247,7 @@ function validateProviderUserInfo(request: any) {
  * @param {any} request The create/edit request object.
  * @param {boolean=} uploadAccountRequest Whether to validate as an uploadAccount request.
  */
-function validateCreateEditRequest(request: any, uploadAccountRequest = false) {
+function validateCreateEditRequest(request: any, uploadAccountRequest = false): void {
   // Hash set of whitelisted parameters.
   const validKeys = {
     displayName: true,
@@ -370,7 +370,7 @@ function validateCreateEditRequest(request: any, uploadAccountRequest = false) {
     const invalidClaims: string[] = [];
     // Check for any invalid claims.
     RESERVED_CLAIMS.forEach((blacklistedClaim) => {
-      if (developerClaims.hasOwnProperty(blacklistedClaim)) {
+      if (Object.prototype.hasOwnProperty.call(developerClaims, blacklistedClaim)) {
         invalidClaims.push(blacklistedClaim);
       }
     });
diff --git a/src/auth/auth-config.ts b/src/auth/auth-config.ts
index ed84a8f2d5..95527eb1a7 100755
--- a/src/auth/auth-config.ts
+++ b/src/auth/auth-config.ts
@@ -179,10 +179,10 @@ export class EmailSignInConfig implements EmailSignInProviderConfig {
   public static buildServerRequest(options: EmailSignInProviderConfig): EmailSignInConfigServerRequest {
     const request: EmailSignInConfigServerRequest = {};
     EmailSignInConfig.validate(options);
-    if (options.hasOwnProperty('enabled')) {
+    if (Object.prototype.hasOwnProperty.call(options, 'enabled')) {
       request.allowPasswordSignup = options.enabled;
     }
-    if (options.hasOwnProperty('passwordRequired')) {
+    if (Object.prototype.hasOwnProperty.call(options, 'passwordRequired')) {
       request.enableEmailLinkSignin = !options.passwordRequired;
     }
     return request;
@@ -193,7 +193,7 @@ export class EmailSignInConfig implements EmailSignInProviderConfig {
    *
    * @param {any} options The options object to validate.
    */
-  private static validate(options: EmailSignInProviderConfig) {
+  private static validate(options: EmailSignInProviderConfig): void {
     // TODO: Validate the request.
     const validKeys = {
       enabled: true,
@@ -349,7 +349,7 @@ export class SAMLConfig implements SAMLAuthProviderConfig {
    * @param {SAMLAuthProviderRequest} options The options object to validate.
    * @param {boolean=} ignoreMissingFields Whether to ignore missing fields.
    */
-  public static validate(options: SAMLAuthProviderRequest, ignoreMissingFields = false) {
+  public static validate(options: SAMLAuthProviderRequest, ignoreMissingFields = false): void {
     const validKeys = {
       enabled: true,
       displayName: true,
@@ -590,7 +590,7 @@ export class OIDCConfig implements OIDCAuthProviderConfig {
    * @param {OIDCAuthProviderRequest} options The options object to validate.
    * @param {boolean=} ignoreMissingFields Whether to ignore missing fields.
    */
-  public static validate(options: OIDCAuthProviderRequest, ignoreMissingFields = false) {
+  public static validate(options: OIDCAuthProviderRequest, ignoreMissingFields = false): void {
     const validKeys = {
       enabled: true,
       displayName: true,
diff --git a/src/auth/auth.ts b/src/auth/auth.ts
index b838802a0f..a79b83c597 100755
--- a/src/auth/auth.ts
+++ b/src/auth/auth.ts
@@ -444,7 +444,7 @@ export class BaseAuth<T extends AbstractAuthRequestHandler> {
         providerConfigs,
       };
       // Delete result.pageToken if undefined.
-      if (response.hasOwnProperty('nextPageToken')) {
+      if (Object.prototype.hasOwnProperty.call(response, 'nextPageToken')) {
         result.pageToken = response.nextPageToken;
       }
       return result;
diff --git a/src/auth/credential.ts b/src/auth/credential.ts
index cb878ff554..43de4d3ed3 100644
--- a/src/auth/credential.ts
+++ b/src/auth/credential.ts
@@ -132,6 +132,7 @@ export class ServiceAccountCredential implements Credential {
       ].join(' '),
     };
 
+    // eslint-disable-next-line @typescript-eslint/no-var-requires
     const jwt = require('jsonwebtoken');
     // This method is actually synchronous so we can capture and return the buffer.
     return jwt.sign(claims, this.privateKey, {
@@ -189,6 +190,7 @@ class ServiceAccount {
       throw new FirebaseAppError(AppErrorCodes.INVALID_CREDENTIAL, errorMessage);
     }
 
+    // eslint-disable-next-line @typescript-eslint/no-var-requires
     const forge = require('node-forge');
     try {
       forge.pki.privateKeyFromPem(this.privateKey);
@@ -386,7 +388,7 @@ export function isApplicationDefault(credential?: Credential): boolean {
  * @param key Name of the property to copy.
  * @param alt Alternative name of the property to copy.
  */
-function copyAttr(to: {[key: string]: any}, from: {[key: string]: any}, key: string, alt: string) {
+function copyAttr(to: {[key: string]: any}, from: {[key: string]: any}, key: string, alt: string): void {
   const tmp = from[key] || from[alt];
   if (typeof tmp !== 'undefined') {
     to[key] = tmp;
diff --git a/src/auth/tenant.ts b/src/auth/tenant.ts
index 4f947aff74..0b2ed1dca9 100755
--- a/src/auth/tenant.ts
+++ b/src/auth/tenant.ts
@@ -95,7 +95,7 @@ export class Tenant {
    * @param {any} request The tenant options object to validate.
    * @param {boolean} createRequest Whether this is a create request.
    */
-  private static validate(request: any, createRequest: boolean) {
+  private static validate(request: any, createRequest: boolean): void {
     const validKeys = {
       displayName: true,
       emailSignInConfig: true,
diff --git a/src/auth/token-generator.ts b/src/auth/token-generator.ts
index f2949a7051..96188af944 100644
--- a/src/auth/token-generator.ts
+++ b/src/auth/token-generator.ts
@@ -101,7 +101,7 @@ export class ServiceAccountSigner implements CryptoSigner {
    * @inheritDoc
    */
   public sign(buffer: Buffer): Promise<Buffer> {
-    const crypto = require('crypto');
+    const crypto = require('crypto'); // eslint-disable-line @typescript-eslint/no-var-requires
     const sign = crypto.createSign('RSA-SHA256');
     sign.update(buffer);
     return Promise.resolve(sign.sign(this.credential.privateKey));
@@ -285,7 +285,7 @@ export class FirebaseTokenGenerator {
     if (typeof developerClaims !== 'undefined') {
       for (const key in developerClaims) {
         /* istanbul ignore else */
-        if (developerClaims.hasOwnProperty(key)) {
+        if (Object.prototype.hasOwnProperty.call(developerClaims, key)) {
           if (BLACKLISTED_CLAIMS.indexOf(key) !== -1) {
             throw new FirebaseAuthError(
               AuthClientErrorCode.INVALID_ARGUMENT,
@@ -311,6 +311,7 @@ export class FirebaseTokenGenerator {
         uid,
       };
       if (this.tenantId) {
+        // eslint-disable-next-line @typescript-eslint/camelcase
         body.tenant_id = this.tenantId;
       }
       if (Object.keys(claims).length > 0) {
@@ -324,9 +325,9 @@ export class FirebaseTokenGenerator {
     });
   }
 
-  private encodeSegment(segment: object | Buffer) {
+  private encodeSegment(segment: object | Buffer): string {
     const buffer: Buffer = (segment instanceof Buffer) ? segment : Buffer.from(JSON.stringify(segment));
-    return toWebSafeBase64(buffer).replace(/\=+$/, '');
+    return toWebSafeBase64(buffer).replace(/=+$/, '');
   }
 
   /**
diff --git a/src/auth/token-verifier.ts b/src/auth/token-verifier.ts
index cd5138d63f..cc0c4f4c02 100644
--- a/src/auth/token-verifier.ts
+++ b/src/auth/token-verifier.ts
@@ -214,7 +214,7 @@ export class FirebaseTokenVerifier {
     }
 
     return this.fetchPublicKeys().then((publicKeys) => {
-      if (!publicKeys.hasOwnProperty(header.kid)) {
+      if (!Object.prototype.hasOwnProperty.call(publicKeys, header.kid)) {
         return Promise.reject(
           new FirebaseAuthError(
             AuthClientErrorCode.INVALID_ARGUMENT,
@@ -299,7 +299,7 @@ export class FirebaseTokenVerifier {
         // error responses.
         throw new HttpError(resp);
       }
-      if (resp.headers.hasOwnProperty('cache-control')) {
+      if (Object.prototype.hasOwnProperty.call(resp.headers, 'cache-control')) {
         const cacheControlHeader: string = resp.headers['cache-control'];
         const parts = cacheControlHeader.split(',');
         parts.forEach((part) => {
diff --git a/src/database/database.ts b/src/database/database.ts
index 379167a694..3da2a356ba 100644
--- a/src/database/database.ts
+++ b/src/database/database.ts
@@ -77,8 +77,8 @@ export class DatabaseService implements FirebaseServiceInterface {
 
     let db: Database = this.INTERNAL.databases[dbUrl];
     if (typeof db === 'undefined') {
-      const rtdb = require('@firebase/database');
-      const { version } = require('../../package.json');
+      const rtdb = require('@firebase/database'); // eslint-disable-line @typescript-eslint/no-var-requires
+      const { version } = require('../../package.json'); // eslint-disable-line @typescript-eslint/no-var-requires
       db = rtdb.initStandalone(this.appInternal, dbUrl, version).instance;
 
       const rulesClient = new DatabaseRulesClient(this.app, dbUrl);
diff --git a/src/firebase-app.ts b/src/firebase-app.ts
index aba82b6cd0..da50651eb3 100644
--- a/src/firebase-app.ts
+++ b/src/firebase-app.ts
@@ -189,7 +189,7 @@ export class FirebaseAppInternals {
    *
    * @param {function(string)} listener The listener that will be called with each new token.
    */
-  public addAuthTokenListener(listener: (token: string) => void) {
+  public addAuthTokenListener(listener: (token: string) => void): void {
     this.tokenListeners_.push(listener);
     if (this.cachedToken_) {
       listener(this.cachedToken_.accessToken);
@@ -201,7 +201,7 @@ export class FirebaseAppInternals {
    *
    * @param {function(string)} listener The listener to remove.
    */
-  public removeAuthTokenListener(listener: (token: string) => void) {
+  public removeAuthTokenListener(listener: (token: string) => void): void {
     this.tokenListeners_ = this.tokenListeners_.filter((other) => other !== listener);
   }
 
diff --git a/src/firebase-namespace.ts b/src/firebase-namespace.ts
index caf58d439d..433659af84 100644
--- a/src/firebase-namespace.ts
+++ b/src/firebase-namespace.ts
@@ -237,7 +237,7 @@ export class FirebaseNamespaceInternals {
    * @param {FirebaseApp} app The FirebaseApp instance whose app hooks to call.
    * @param {string} eventName The event name representing which app hooks to call.
    */
-  private callAppHooks_(app: FirebaseApp, eventName: string) {
+  private callAppHooks_(app: FirebaseApp, eventName: string): void {
     Object.keys(this.serviceFactories).forEach((serviceName) => {
       if (this.appHooks_[serviceName]) {
         this.appHooks_[serviceName](eventName, app);
@@ -340,6 +340,8 @@ export class FirebaseNamespace {
     const fn: FirebaseServiceNamespace<Database> = (app?: FirebaseApp) => {
       return this.ensureApp(app).database();
     };
+
+    // eslint-disable-next-line @typescript-eslint/no-var-requires
     return Object.assign(fn, require('@firebase/database'));
   }
 
@@ -375,6 +377,8 @@ export class FirebaseNamespace {
     let fn: FirebaseServiceNamespace<Firestore> = (app?: FirebaseApp) => {
       return this.ensureApp(app).firestore();
     };
+
+    // eslint-disable-next-line @typescript-eslint/no-var-requires
     const firestore = require('@google-cloud/firestore');
 
     fn = Object.assign(fn, firestore.Firestore);
diff --git a/src/firestore/firestore.ts b/src/firestore/firestore.ts
index c733321da7..89e7fe2771 100644
--- a/src/firestore/firestore.ts
+++ b/src/firestore/firestore.ts
@@ -73,12 +73,13 @@ export function getFirestoreOptions(app: FirebaseApp): Settings {
 
   const projectId: string | null = utils.getExplicitProjectId(app);
   const credential = app.options.credential;
+  // eslint-disable-next-line @typescript-eslint/no-var-requires
   const { version: firebaseVersion } = require('../../package.json');
   if (credential instanceof ServiceAccountCredential) {
     return {
       credentials: {
-        private_key: credential.privateKey,
-        client_email: credential.clientEmail,
+        private_key: credential.privateKey, // eslint-disable-line @typescript-eslint/camelcase
+        client_email: credential.clientEmail, // eslint-disable-line @typescript-eslint/camelcase
       },
       // When the SDK is initialized with ServiceAccountCredentials an explicit projectId is
       // guaranteed to be available.
diff --git a/src/index.d.ts b/src/index.d.ts
index 8ee67a49fe..af8a938766 100755
--- a/src/index.d.ts
+++ b/src/index.d.ts
@@ -18,6 +18,8 @@ import { Bucket } from '@google-cloud/storage';
 import * as _firestore from '@google-cloud/firestore';
 import { Agent } from 'http';
 
+/* eslint-disable @typescript-eslint/ban-types */
+
 /**
  * `admin` is a global namespace from which all Firebase Admin
  * services are accessed.
diff --git a/src/messaging/messaging-types.ts b/src/messaging/messaging-types.ts
index bd25f164cb..27891d27ed 100644
--- a/src/messaging/messaging-types.ts
+++ b/src/messaging/messaging-types.ts
@@ -297,7 +297,7 @@ export interface SendResponse {
  *
  * @param {Message} Message An object to be validated.
  */
-export function validateMessage(message: Message) {
+export function validateMessage(message: Message): void {
   if (!validator.isNonNullObject(message)) {
     throw new FirebaseMessagingError(
       MessagingClientErrorCode.INVALID_PAYLOAD, 'Message must be a non-null object');
@@ -337,7 +337,7 @@ export function validateMessage(message: Message) {
  * @param {object} map An object to be validated.
  * @param {string} label A label to be included in the errors thrown.
  */
-function validateStringMap(map: {[key: string]: any} | undefined, label: string) {
+function validateStringMap(map: {[key: string]: any} | undefined, label: string): void {
   if (typeof map === 'undefined') {
     return;
   } else if (!validator.isNonNullObject(map)) {
@@ -357,7 +357,7 @@ function validateStringMap(map: {[key: string]: any} | undefined, label: string)
  *
  * @param {WebpushConfig} config An object to be validated.
  */
-function validateWebpushConfig(config: WebpushConfig | undefined) {
+function validateWebpushConfig(config: WebpushConfig | undefined): void {
   if (typeof config === 'undefined') {
     return;
   } else if (!validator.isNonNullObject(config)) {
@@ -374,7 +374,7 @@ function validateWebpushConfig(config: WebpushConfig | undefined) {
  *
  * @param {ApnsConfig} config An object to be validated.
  */
-function validateApnsConfig(config: ApnsConfig | undefined) {
+function validateApnsConfig(config: ApnsConfig | undefined): void {
   if (typeof config === 'undefined') {
     return;
   } else if (!validator.isNonNullObject(config)) {
@@ -391,7 +391,7 @@ function validateApnsConfig(config: ApnsConfig | undefined) {
  *
  * @param {ApnsFcmOptions} fcmOptions An object to be validated.
  */
-function validateApnsFcmOptions(fcmOptions: ApnsFcmOptions | undefined) {
+function validateApnsFcmOptions(fcmOptions: ApnsFcmOptions | undefined): void {
   if (typeof fcmOptions === 'undefined') {
     return;
   } else if (!validator.isNonNullObject(fcmOptions)) {
@@ -429,7 +429,7 @@ function validateApnsFcmOptions(fcmOptions: ApnsFcmOptions | undefined) {
  *
  * @param {FcmOptions} fcmOptions An object to be validated.
  */
-function validateFcmOptions(fcmOptions: FcmOptions | undefined) {
+function validateFcmOptions(fcmOptions: FcmOptions | undefined): void {
   if (typeof fcmOptions === 'undefined') {
     return;
   } else if (!validator.isNonNullObject(fcmOptions)) {
@@ -448,7 +448,7 @@ function validateFcmOptions(fcmOptions: FcmOptions | undefined) {
  *
  * @param {Notification} notification An object to be validated.
  */
-function validateNotification(notification: Notification | undefined) {
+function validateNotification(notification: Notification | undefined): void {
   if (typeof notification === 'undefined') {
     return;
   } else if (!validator.isNonNullObject(notification)) {
@@ -479,7 +479,7 @@ function validateNotification(notification: Notification | undefined) {
  *
  * @param {ApnsPayload} payload An object to be validated.
  */
-function validateApnsPayload(payload: ApnsPayload | undefined) {
+function validateApnsPayload(payload: ApnsPayload | undefined): void {
   if (typeof payload === 'undefined') {
     return;
   } else if (!validator.isNonNullObject(payload)) {
@@ -495,7 +495,7 @@ function validateApnsPayload(payload: ApnsPayload | undefined) {
  *
  * @param {Aps} aps An object to be validated.
  */
-function validateAps(aps: Aps) {
+function validateAps(aps: Aps): void {
   if (typeof aps === 'undefined') {
     return;
   } else if (!validator.isNonNullObject(aps)) {
@@ -537,7 +537,7 @@ function validateAps(aps: Aps) {
   }
 }
 
-function validateApsSound(sound: string | CriticalSound | undefined) {
+function validateApsSound(sound: string | CriticalSound | undefined): void {
   if (typeof sound === 'undefined' || validator.isNonEmptyString(sound)) {
     return;
   } else if (!validator.isNonNullObject(sound)) {
@@ -583,7 +583,7 @@ function validateApsSound(sound: string | CriticalSound | undefined) {
  *
  * @param {string | ApsAlert} alert An alert string or an object to be validated.
  */
-function validateApsAlert(alert: string | ApsAlert | undefined) {
+function validateApsAlert(alert: string | ApsAlert | undefined): void {
   if (typeof alert === 'undefined' || validator.isString(alert)) {
     return;
   } else if (!validator.isNonNullObject(alert)) {
@@ -632,7 +632,7 @@ function validateApsAlert(alert: string | ApsAlert | undefined) {
  *
  * @param {AndroidConfig} config An object to be validated.
  */
-function validateAndroidConfig(config: AndroidConfig | undefined) {
+function validateAndroidConfig(config: AndroidConfig | undefined): void {
   if (typeof config === 'undefined') {
     return;
   } else if (!validator.isNonNullObject(config)) {
@@ -667,7 +667,7 @@ function validateAndroidConfig(config: AndroidConfig | undefined) {
  *
  * @param {AndroidNotification} notification An object to be validated.
  */
-function validateAndroidNotification(notification: AndroidNotification | undefined) {
+function validateAndroidNotification(notification: AndroidNotification | undefined): void {
   if (typeof notification === 'undefined') {
     return;
   } else if (!validator.isNonNullObject(notification)) {
@@ -767,7 +767,7 @@ function validateAndroidNotification(notification: AndroidNotification | undefin
  *
  * @param {LightSettings} lightSettings An object to be validated.
  */
-function validateLightSettings(lightSettings?: LightSettings) {
+function validateLightSettings(lightSettings?: LightSettings): void {
   if (typeof lightSettings === 'undefined') {
     return;
   } else if (!validator.isNonNullObject(lightSettings)) {
@@ -824,7 +824,7 @@ function validateLightSettings(lightSettings?: LightSettings) {
  *
  * @param {AndroidFcmOptions} fcmOptions An object to be validated.
  */
-function validateAndroidFcmOptions(fcmOptions: AndroidFcmOptions | undefined) {
+function validateAndroidFcmOptions(fcmOptions: AndroidFcmOptions | undefined): void {
   if (typeof fcmOptions === 'undefined') {
     return;
   } else if (!validator.isNonNullObject(fcmOptions)) {
diff --git a/src/messaging/messaging.ts b/src/messaging/messaging.ts
index faee5f29a1..6cabb1104b 100644
--- a/src/messaging/messaging.ts
+++ b/src/messaging/messaging.ts
@@ -32,6 +32,8 @@ import {
 import * as utils from '../utils';
 import * as validator from '../utils/validator';
 
+/* eslint-disable @typescript-eslint/camelcase */
+
 // FCM endpoints
 const FCM_SEND_HOST = 'fcm.googleapis.com';
 const FCM_SEND_PATH = '/fcm/send';
@@ -718,7 +720,7 @@ export class Messaging implements FirebaseServiceInterface {
   private validateMessagingPayloadAndOptionsTypes(
     payload: MessagingPayload,
     options: MessagingOptions,
-  ) {
+  ): void {
     // Validate the payload is an object
     if (!validator.isNonNullObject(payload)) {
       throw new FirebaseMessagingError(
@@ -744,7 +746,7 @@ export class Messaging implements FirebaseServiceInterface {
    * @return {MessagingPayload} A copy of the provided payload with whitelisted properties switched
    *     from camelCase to underscore_case.
    */
-  private validateMessagingPayload(payload: MessagingPayload) {
+  private validateMessagingPayload(payload: MessagingPayload): MessagingPayload {
     const payloadCopy: MessagingPayload = deepCopy(payload);
 
     const payloadKeys = Object.keys(payloadCopy);
@@ -772,7 +774,7 @@ export class Messaging implements FirebaseServiceInterface {
       );
     }
 
-    const validatePayload = (payloadKey: string, value: DataMessagePayload | NotificationMessagePayload) => {
+    const validatePayload = (payloadKey: string, value: DataMessagePayload | NotificationMessagePayload): void => {
       // Validate each top-level key in the payload is an object
       if (!validator.isNonNullObject(value)) {
         throw new FirebaseMessagingError(
@@ -835,7 +837,7 @@ export class Messaging implements FirebaseServiceInterface {
    * @return {MessagingOptions} A copy of the provided options with whitelisted properties switched
    *   from camelCase to underscore_case.
    */
-  private validateMessagingOptions(options: MessagingOptions) {
+  private validateMessagingOptions(options: MessagingOptions): MessagingOptions {
     const optionsCopy: MessagingOptions = deepCopy(options);
 
     // Validate the options object does not contain blacklisted properties
@@ -917,7 +919,7 @@ export class Messaging implements FirebaseServiceInterface {
     registrationTokenOrTokens: string | string[],
     methodName: string,
     errorInfo: ErrorInfo = MessagingClientErrorCode.INVALID_ARGUMENT,
-  ) {
+  ): void {
     if (!validator.isNonEmptyArray(registrationTokenOrTokens) &&
         !validator.isNonEmptyString(registrationTokenOrTokens)) {
       throw new FirebaseMessagingError(
@@ -940,7 +942,7 @@ export class Messaging implements FirebaseServiceInterface {
     registrationTokenOrTokens: string | string[],
     methodName: string,
     errorInfo: ErrorInfo = MessagingClientErrorCode.INVALID_ARGUMENT,
-  ) {
+  ): void {
     if (validator.isArray(registrationTokenOrTokens)) {
       // Validate the array contains no more than 1,000 registration tokens.
       if (registrationTokenOrTokens.length > 1000) {
@@ -975,7 +977,7 @@ export class Messaging implements FirebaseServiceInterface {
     topic: string | string[],
     methodName: string,
     errorInfo: ErrorInfo = MessagingClientErrorCode.INVALID_ARGUMENT,
-  ) {
+  ): void {
     if (!validator.isNonEmptyString(topic)) {
       throw new FirebaseMessagingError(
         errorInfo,
@@ -996,7 +998,7 @@ export class Messaging implements FirebaseServiceInterface {
     topic: string,
     methodName: string,
     errorInfo: ErrorInfo = MessagingClientErrorCode.INVALID_ARGUMENT,
-  ) {
+  ): void {
     if (!validator.isTopic(topic)) {
       throw new FirebaseMessagingError(
         errorInfo,
@@ -1013,7 +1015,7 @@ export class Messaging implements FirebaseServiceInterface {
    *
    * @return {string} The normalized topic name.
    */
-  private normalizeTopic(topic: string) {
+  private normalizeTopic(topic: string): string {
     if (!/^\/topics\//.test(topic)) {
       topic = `/topics/${ topic }`;
     }
diff --git a/src/project-management/android-app.ts b/src/project-management/android-app.ts
index e51ace8ba3..0cbd8951fc 100644
--- a/src/project-management/android-app.ts
+++ b/src/project-management/android-app.ts
@@ -46,7 +46,7 @@ export class AndroidApp {
           assertServerResponse(
             validator.isNonEmptyString(responseData[requiredField]),
             responseData,
-            `getMetadata()\'s responseData.${requiredField} must be a non-empty string.`);
+            `getMetadata()'s responseData.${requiredField} must be a non-empty string.`);
         });
 
         const metadata: AndroidAppMetadata = {
@@ -89,7 +89,7 @@ export class AndroidApp {
             assertServerResponse(
               validator.isNonEmptyString(certificateJson[requiredField]),
               responseData,
-              `getShaCertificates()\'s responseData.certificates[].${requiredField} must be a `
+              `getShaCertificates()'s responseData.certificates[].${requiredField} must be a `
                       + `non-empty string.`);
           });
 
@@ -128,7 +128,7 @@ export class AndroidApp {
         assertServerResponse(
           validator.isBase64String(base64ConfigFileContents),
           responseData,
-          `getConfig()\'s responseData.configFileContents must be a base64 string.`);
+          `getConfig()'s responseData.configFileContents must be a base64 string.`);
 
         return Buffer.from(base64ConfigFileContents, 'base64').toString('utf8');
       });
diff --git a/src/project-management/ios-app.ts b/src/project-management/ios-app.ts
index 46672a9306..18acb47ae1 100644
--- a/src/project-management/ios-app.ts
+++ b/src/project-management/ios-app.ts
@@ -46,7 +46,7 @@ export class IosApp {
           assertServerResponse(
             validator.isNonEmptyString(responseData[requiredField]),
             responseData,
-            `getMetadata()\'s responseData.${requiredField} must be a non-empty string.`);
+            `getMetadata()'s responseData.${requiredField} must be a non-empty string.`);
         });
 
         const metadata: IosAppMetadata = {
@@ -81,7 +81,7 @@ export class IosApp {
         assertServerResponse(
           validator.isBase64String(base64ConfigFileContents),
           responseData,
-          `getConfig()\'s responseData.configFileContents must be a base64 string.`);
+          `getConfig()'s responseData.configFileContents must be a base64 string.`);
 
         return Buffer.from(base64ConfigFileContents, 'base64').toString('utf8');
       });
diff --git a/src/project-management/project-management-api-request.ts b/src/project-management/project-management-api-request.ts
index 6acd692cdd..c7528f9157 100644
--- a/src/project-management/project-management-api-request.ts
+++ b/src/project-management/project-management-api-request.ts
@@ -64,7 +64,7 @@ export class ProjectManagementRequestHandler {
       `https://${PROJECT_MANAGEMENT_HOST_AND_PORT}${PROJECT_MANAGEMENT_BETA_PATH}`;
   private readonly httpClient: AuthorizedHttpClient;
 
-  private static wrapAndRethrowHttpError(errStatusCode: number, errText?: string) {
+  private static wrapAndRethrowHttpError(errStatusCode: number, errText?: string): void {
     let errorCode: ProjectManagementErrorCode;
     let errorMessage: string;
 
diff --git a/src/project-management/project-management.ts b/src/project-management/project-management.ts
index 218e0a5977..dfe6be3a3f 100644
--- a/src/project-management/project-management.ts
+++ b/src/project-management/project-management.ts
@@ -261,7 +261,7 @@ export class ProjectManagement implements FirebaseServiceInterface {
     assertServerResponse(
       validator.isNonNullObject(responseData),
       responseData,
-      `${callerName}\'s responseData must be a non-null object.`);
+      `${callerName}'s responseData must be a non-null object.`);
 
     if (responseData.apps) {
       assertServerResponse(
diff --git a/src/storage/storage.ts b/src/storage/storage.ts
index 6b3ddcaef1..afd3b003de 100644
--- a/src/storage/storage.ts
+++ b/src/storage/storage.ts
@@ -79,8 +79,8 @@ export class Storage implements FirebaseServiceInterface {
         // guaranteed to be available.
         projectId: projectId!,
         credentials: {
-          private_key: credential.privateKey,
-          client_email: credential.clientEmail,
+          private_key: credential.privateKey, // eslint-disable-line @typescript-eslint/camelcase
+          client_email: credential.clientEmail, // eslint-disable-line @typescript-eslint/camelcase
         },
       });
     } else if (isApplicationDefault(app.options.credential)) {
diff --git a/src/utils/api-request.ts b/src/utils/api-request.ts
index 661cc50477..9f1b8c18ca 100644
--- a/src/utils/api-request.ts
+++ b/src/utils/api-request.ts
@@ -213,7 +213,7 @@ export function defaultRetryConfig(): RetryConfig {
  *
  * @param retry The configuration to be validated.
  */
-function validateRetryConfig(retry: RetryConfig) {
+function validateRetryConfig(retry: RetryConfig): void {
   if (!validator.isNumber(retry.maxRetries) || retry.maxRetries < 0) {
     throw new FirebaseAppError(
       AppErrorCodes.INVALID_ARGUMENT, 'maxRetries must be a non-negative integer');
@@ -481,7 +481,7 @@ class AsyncHttpCall {
     }
   }
 
-  private execute() {
+  private execute(): void {
     const transport: any = this.options.protocol === 'https:' ? https : http;
     const req: http.ClientRequest = transport.request(this.options, (res: http.IncomingMessage) => {
       this.handleResponse(res, req);
@@ -508,7 +508,7 @@ class AsyncHttpCall {
     req.end(this.entity);
   }
 
-  private handleResponse(res: http.IncomingMessage, req: http.ClientRequest) {
+  private handleResponse(res: http.IncomingMessage, req: http.ClientRequest): void {
     if (req.aborted) {
       return;
     }
@@ -572,7 +572,7 @@ class AsyncHttpCall {
     const encodings = ['gzip', 'compress', 'deflate'];
     if (res.headers['content-encoding'] && encodings.indexOf(res.headers['content-encoding']) !== -1) {
       // Add the unzipper to the body stream processing pipeline.
-      const zlib: typeof zlibmod = require('zlib');
+      const zlib: typeof zlibmod = require('zlib'); // eslint-disable-line @typescript-eslint/no-var-requires
       respStream = respStream.pipe(zlib.createUnzip());
       // Remove the content-encoding in order to not confuse downstream operations.
       delete res.headers['content-encoding'];
@@ -581,9 +581,9 @@ class AsyncHttpCall {
   }
 
   private handleMultipartResponse(
-    response: LowLevelResponse, respStream: Readable, boundary: string) {
+    response: LowLevelResponse, respStream: Readable, boundary: string): void {
 
-    const dicer = require('dicer');
+    const dicer = require('dicer'); // eslint-disable-line @typescript-eslint/no-var-requires
     const multipartParser = new dicer({boundary});
     const responseBuffer: Buffer[] = [];
     multipartParser.on('part', (part: any) => {
@@ -607,7 +607,7 @@ class AsyncHttpCall {
     respStream.pipe(multipartParser);
   }
 
-  private handleRegularResponse(response: LowLevelResponse, respStream: Readable) {
+  private handleRegularResponse(response: LowLevelResponse, respStream: Readable): void {
     const responseBuffer: Buffer[] = [];
     respStream.on('data', (chunk: Buffer) => {
       responseBuffer.push(chunk);
@@ -631,7 +631,7 @@ class AsyncHttpCall {
    * Finalizes the current HTTP call in-flight by either resolving or rejecting the associated
    * promise. In the event of an error, adds additional useful information to the returned error.
    */
-  private finalizeResponse(response: LowLevelResponse) {
+  private finalizeResponse(response: LowLevelResponse): void {
     if (response.status >= 200 && response.status < 300) {
       this.resolve(response);
     } else {
@@ -652,7 +652,7 @@ class AsyncHttpCall {
     message: string,
     code?: string | null,
     request?: http.ClientRequest | null,
-    response?: LowLevelResponse) {
+    response?: LowLevelResponse): void {
 
     const error = new Error(message);
     this.enhanceAndReject(error, code, request, response);
@@ -662,7 +662,7 @@ class AsyncHttpCall {
     error: any,
     code?: string | null,
     request?: http.ClientRequest | null,
-    response?: LowLevelResponse) {
+    response?: LowLevelResponse): void {
 
     this.reject(this.enhanceError(error, code, request, response));
   }
@@ -778,7 +778,7 @@ class HttpRequestConfigImpl implements HttpRequestConfig {
     const parsedUrl = new url.URL(fullUrl);
     const dataObj = this.data as {[key: string]: string};
     for (const key in dataObj) {
-      if (dataObj.hasOwnProperty(key)) {
+      if (Object.prototype.hasOwnProperty.call(dataObj, key)) {
         parsedUrl.searchParams.append(key, dataObj[key]);
       }
     }
diff --git a/src/utils/deep-copy.ts b/src/utils/deep-copy.ts
index 2cff483604..72a791d30a 100644
--- a/src/utils/deep-copy.ts
+++ b/src/utils/deep-copy.ts
@@ -69,7 +69,7 @@ export function deepExtend(target: any, source: any): any {
   }
 
   for (const prop in source) {
-    if (!source.hasOwnProperty(prop)) {
+    if (!Object.prototype.hasOwnProperty.call(source, prop)) {
       continue;
     }
     target[prop] = deepExtend(target[prop], source[prop]);
diff --git a/src/utils/index.ts b/src/utils/index.ts
index f0d7eee394..f6e2f41232 100755
--- a/src/utils/index.ts
+++ b/src/utils/index.ts
@@ -151,7 +151,7 @@ export function generateUpdateMask(obj: {[key: string]: any}): string[] {
     return updateMask;
   }
   for (const key in obj) {
-    if (obj.hasOwnProperty(key) && typeof obj[key] !== 'undefined') {
+    if (Object.prototype.hasOwnProperty.call(obj, key) && typeof obj[key] !== 'undefined') {
       const maskList = generateUpdateMask(obj[key]);
       if (maskList.length > 0) {
         maskList.forEach((mask) => {
diff --git a/src/utils/validator.ts b/src/utils/validator.ts
index 8edc54a97e..9c24d78211 100644
--- a/src/utils/validator.ts
+++ b/src/utils/validator.ts
@@ -198,7 +198,7 @@ export function isURL(urlStr: any): boolean {
     return false;
   }
   // Lookup illegal characters.
-  const re = /[^a-z0-9\:\/\?\#\[\]\@\!\$\&\'\(\)\*\+\,\;\=\.\-\_\~\%]/i;
+  const re = /[^a-z0-9:/?#[\]@!$&'()*+,;=.\-_~%]/i;
   if (re.test(urlStr)) {
     return false;
   }
@@ -213,12 +213,12 @@ export function isURL(urlStr: any): boolean {
     }
     // Validate hostname: Can contain letters, numbers, underscore and dashes separated by a dot.
     // Each zone must not start with a hyphen or underscore.
-    if (!hostname || !/^[a-zA-Z0-9]+[\w\-]*([\.]?[a-zA-Z0-9]+[\w\-]*)*$/.test(hostname)) {
+    if (!hostname || !/^[a-zA-Z0-9]+[\w-]*([.]?[a-zA-Z0-9]+[\w-]*)*$/.test(hostname)) {
       return false;
     }
     // Allow for pathnames: (/chars+)*/?
     // Where chars can be a combination of: a-z A-Z 0-9 - _ . ~ ! $ & ' ( ) * + , ; = : @ %
-    const pathnameRe = /^(\/[\w\-\.\~\!\$\'\(\)\*\+\,\;\=\:\@\%]+)*\/?$/;
+    const pathnameRe = /^(\/[\w\-.~!$'()*+,;=:@%]+)*\/?$/;
     // Validate pathname.
     if (pathname &&
         pathname !== '/' &&
diff --git a/test/integration/auth.spec.ts b/test/integration/auth.spec.ts
index 9e43c92abd..3bd65422cd 100755
--- a/test/integration/auth.spec.ts
+++ b/test/integration/auth.spec.ts
@@ -32,9 +32,7 @@ import { AuthProviderConfig } from '../../src/auth/auth-config';
 import { deepExtend, deepCopy } from '../../src/utils/deep-copy';
 import { User, FirebaseAuth } from '@firebase/auth-types';
 
-/* tslint:disable:no-var-requires */
-const chalk = require('chalk');
-/* tslint:enable:no-var-requires */
+const chalk = require('chalk'); // eslint-disable-line @typescript-eslint/no-var-requires
 
 chai.should();
 chai.use(chaiAsPromised);
@@ -292,7 +290,7 @@ describe('admin.auth', () => {
       .then((decodedIdToken: {[key: string]: any}) => {
         // Confirm expected claims set on the user's ID token.
         for (const key in customClaims) {
-          if (customClaims.hasOwnProperty(key)) {
+          if (Object.prototype.hasOwnProperty.call(customClaims, key)) {
             expect(decodedIdToken[key]).to.equal(customClaims[key]);
           }
         }
@@ -316,7 +314,7 @@ describe('admin.auth', () => {
       .then((decodedIdToken: {[key: string]: any}) => {
         // Confirm all custom claims are cleared.
         for (const key in customClaims) {
-          if (customClaims.hasOwnProperty(key)) {
+          if (Object.prototype.hasOwnProperty.call(customClaims, key)) {
             expect(decodedIdToken[key]).to.be.undefined;
           }
         }
@@ -969,7 +967,7 @@ describe('admin.auth', () => {
       enableRequestSigning: true,
     };
 
-    const removeTempConfigs = () => {
+    const removeTempConfigs = (): Promise<any> => {
       return Promise.all([
         admin.auth().deleteProviderConfig(authProviderConfig1.providerId).catch(() => {/* empty */}),
         admin.auth().deleteProviderConfig(authProviderConfig2.providerId).catch(() => {/* empty */}),
@@ -1101,7 +1099,7 @@ describe('admin.auth', () => {
       clientId: 'CLIENT_ID2',
     };
 
-    const removeTempConfigs = () => {
+    const removeTempConfigs = (): Promise<any> => {
       return Promise.all([
         admin.auth().deleteProviderConfig(authProviderConfig1.providerId).catch(() => {/* empty */}),
         admin.auth().deleteProviderConfig(authProviderConfig2.providerId).catch(() => {/* empty */}),
@@ -1619,7 +1617,7 @@ function testImportAndSignInUser(
  * @return {Promise} A promise that resolves when the user is deleted
  *     or is found not to exist.
  */
-function deletePhoneNumberUser(phoneNumber: string) {
+function deletePhoneNumberUser(phoneNumber: string): Promise<void> {
   return admin.auth().getUserByPhoneNumber(phoneNumber)
     .then((userRecord) => {
       return safeDelete(userRecord.uid);
@@ -1638,7 +1636,7 @@ function deletePhoneNumberUser(phoneNumber: string) {
  *
  * @return {Promise} A promise that resolves when test preparations are ready.
  */
-function cleanup() {
+function cleanup(): Promise<any> {
   // Delete any existing users that could affect the test outcome.
   const promises: Array<Promise<void>> = [
     deletePhoneNumberUser(testPhoneNumber),
@@ -1729,9 +1727,9 @@ function safeDelete(uid: string): Promise<void> {
  * @param {[key: string]: any} expected object.
  * @param {[key: string]: any} actual object.
  */
-function assertDeepEqualUnordered(expected: {[key: string]: any}, actual: {[key: string]: any}) {
+function assertDeepEqualUnordered(expected: {[key: string]: any}, actual: {[key: string]: any}): void {
   for (const key in expected) {
-    if (expected.hasOwnProperty(key)) {
+    if (Object.prototype.hasOwnProperty.call(expected, key)) {
       expect(actual[key])
         .to.deep.equal(expected[key]);
     }
diff --git a/test/integration/database.spec.ts b/test/integration/database.spec.ts
index 1419313416..7fed7be2a0 100644
--- a/test/integration/database.spec.ts
+++ b/test/integration/database.spec.ts
@@ -19,9 +19,8 @@ import * as chai from 'chai';
 import * as chaiAsPromised from 'chai-as-promised';
 import {defaultApp, nullApp, nonNullApp, cmdArgs, databaseUrl} from './setup';
 
-/* tslint:disable:no-var-requires */
+// eslint-disable-next-line @typescript-eslint/no-var-requires
 const chalk = require('chalk');
-/* tslint:enable:no-var-requires */
 
 chai.should();
 chai.use(chaiAsPromised);
@@ -178,7 +177,7 @@ describe('admin.database', () => {
 // eslint-disable-next-line @typescript-eslint/no-unused-vars
 function addValueEventListener(
   db: admin.database.Database,
-  callback: (s: admin.database.DataSnapshot | null) => any) {
+  callback: (s: admin.database.DataSnapshot | null) => any): void {
   const eventType: admin.database.EventType = 'value';
   db.ref().on(eventType, callback);
 }
diff --git a/test/integration/project-management.spec.ts b/test/integration/project-management.spec.ts
index 9fbf4c73e0..de26f4aaf2 100644
--- a/test/integration/project-management.spec.ts
+++ b/test/integration/project-management.spec.ts
@@ -264,21 +264,21 @@ function deleteAllShaCertificates(androidApp: admin.projectManagement.AndroidApp
 /**
  * @return {string} Dot-separated string that can be used as a unique package name or bundle ID.
  */
-function generateUniqueAppNamespace() {
+function generateUniqueAppNamespace(): string {
   return APP_NAMESPACE_PREFIX + generateRandomString(APP_NAMESPACE_SUFFIX_LENGTH);
 }
 
 /**
  * @return {string} Dot-separated string that can be used as a unique app display name.
  */
-function generateUniqueAppDisplayName() {
+function generateUniqueAppDisplayName(): string {
   return APP_DISPLAY_NAME_PREFIX + generateRandomString(APP_DISPLAY_NAME_SUFFIX_LENGTH);
 }
 
 /**
  * @return {string} string that can be used as a unique project display name.
  */
-function generateUniqueProjectDisplayName() {
+function generateUniqueProjectDisplayName(): string {
   return PROJECT_DISPLAY_NAME_PREFIX + generateRandomString(PROJECT_DISPLAY_NAME_SUFFIX_LENGTH);
 }
 
diff --git a/test/integration/security-rules.spec.ts b/test/integration/security-rules.spec.ts
index ce86ed932e..648b74c787 100644
--- a/test/integration/security-rules.spec.ts
+++ b/test/integration/security-rules.spec.ts
@@ -47,11 +47,11 @@ describe('admin.securityRules', () => {
 
   const rulesetsToDelete: string[] = [];
 
-  function scheduleForDelete(ruleset: admin.securityRules.Ruleset) {
+  function scheduleForDelete(ruleset: admin.securityRules.Ruleset): void {
     rulesetsToDelete.push(ruleset.name);
   }
 
-  function unscheduleForDelete(ruleset: admin.securityRules.Ruleset) {
+  function unscheduleForDelete(ruleset: admin.securityRules.Ruleset): void {
     rulesetsToDelete.splice(rulesetsToDelete.indexOf(ruleset.name), 1);
   }
 
@@ -296,7 +296,7 @@ describe('admin.securityRules', () => {
     });
   });
 
-  function verifyFirestoreRuleset(ruleset: admin.securityRules.Ruleset) {
+  function verifyFirestoreRuleset(ruleset: admin.securityRules.Ruleset): void {
     expect(ruleset.name).to.match(RULESET_NAME_PATTERN);
     const createTime = new Date(ruleset.createTime);
     expect(ruleset.createTime).equals(createTime.toUTCString());
diff --git a/test/integration/setup.ts b/test/integration/setup.ts
index 8b5dfcda71..a3558ae6b2 100644
--- a/test/integration/setup.ts
+++ b/test/integration/setup.ts
@@ -21,9 +21,8 @@ import path = require('path');
 import {random} from 'lodash';
 import { Credential, GoogleOAuthAccessToken } from '../../src/auth/credential';
 
-/* tslint:disable:no-var-requires */
+// eslint-disable-next-line @typescript-eslint/no-var-requires
 const chalk = require('chalk');
-/* tslint:enable:no-var-requires */
 
 export let databaseUrl: string;
 export let storageBucket: string;
diff --git a/test/integration/typescript/src/example.test.ts b/test/integration/typescript/src/example.test.ts
index 25676d96be..67a1ce6272 100644
--- a/test/integration/typescript/src/example.test.ts
+++ b/test/integration/typescript/src/example.test.ts
@@ -21,6 +21,7 @@ import {Firestore} from '@google-cloud/firestore';
 
 import * as admin from 'firebase-admin';
 
+// eslint-disable-next-line @typescript-eslint/no-var-requires
 const serviceAccount = require('../mock.key.json');
 
 describe('Init App', () => {
diff --git a/test/integration/typescript/src/example.ts b/test/integration/typescript/src/example.ts
index 9e75838efa..0b254517d1 100644
--- a/test/integration/typescript/src/example.ts
+++ b/test/integration/typescript/src/example.ts
@@ -16,7 +16,7 @@
 
 import * as firebase from 'firebase-admin';
 
-export function initApp(serviceAcct: any, name: string) {
+export function initApp(serviceAcct: any, name: string): firebase.app.App {
   return firebase.initializeApp({
     credential: firebase.credential.cert(serviceAcct),
     databaseURL: 'https://mock.firebaseio.com'
@@ -26,7 +26,7 @@ export function initApp(serviceAcct: any, name: string) {
 export function addValueEventListener(
   // Check for type compilation
   db: firebase.database.Database,
-  callback: (s: firebase.database.DataSnapshot) => any) {
+  callback: (s: firebase.database.DataSnapshot) => any): void {
   const eventType: firebase.database.EventType = 'value';
   db.ref().on(eventType, callback);
 }
diff --git a/test/resources/mocks.ts b/test/resources/mocks.ts
index c2c3dd3aa1..7c73e8fe54 100644
--- a/test/resources/mocks.ts
+++ b/test/resources/mocks.ts
@@ -81,8 +81,8 @@ export const appOptionsAuthDB: FirebaseAppOptions = {
 export class MockCredential implements Credential {
   public getAccessToken(): Promise<GoogleOAuthAccessToken> {
     return Promise.resolve({
-      access_token: 'mock-token',
-      expires_in: 3600,
+      access_token: 'mock-token', // eslint-disable-line @typescript-eslint/camelcase
+      expires_in: 3600, // eslint-disable-line @typescript-eslint/camelcase
     });
   }
 }
@@ -144,9 +144,8 @@ export const refreshToken = {
   type: 'refreshToken',
 };
 
-/* tslint:disable:no-var-requires */
+// eslint-disable-next-line @typescript-eslint/no-var-requires
 export const certificateObject = require('./mock.key.json');
-/* tslint:enable:no-var-requires */
 
 // Randomly generated key pairs that don't correspond to anything related to Firebase or GCP
 export const keyPairs = [
diff --git a/test/unit/auth/auth-api-request.spec.ts b/test/unit/auth/auth-api-request.spec.ts
index 5b4cd722ff..6c225b817a 100755
--- a/test/unit/auth/auth-api-request.spec.ts
+++ b/test/unit/auth/auth-api-request.spec.ts
@@ -547,7 +547,7 @@ describe('FIREBASE_AUTH_SET_ACCOUNT_INFO', () => {
         expect(() => {
           const claims = {
             sub: 'sub',
-            auth_time: 'time',
+            auth_time: 'time', // eslint-disable-line @typescript-eslint/camelcase
           };
           return requestValidator({localId: '1234', customAttributes: JSON.stringify(claims)});
         }).to.throw(`Developer claims "auth_time", "sub" are reserved and cannot be specified.`);
diff --git a/test/unit/auth/auth.spec.ts b/test/unit/auth/auth.spec.ts
index fc75b0d2dc..5c453d18e8 100755
--- a/test/unit/auth/auth.spec.ts
+++ b/test/unit/auth/auth.spec.ts
@@ -73,7 +73,7 @@ interface EmailActionTest {
  * @return {object} A sample valid server response as returned from getAccountInfo
  *     endpoint.
  */
-function getValidGetAccountInfoResponse(tenantId?: string) {
+function getValidGetAccountInfoResponse(tenantId?: string): {kind: string; users: any[]} {
   const userResponse: any = {
     localId: 'abcdefghijklmnopqrstuvwxyz',
     email: 'user@gmail.com',
@@ -123,7 +123,7 @@ function getValidGetAccountInfoResponse(tenantId?: string) {
  * @param {any} serverResponse Raw getAccountInfo response.
  * @return {Object} The corresponding user record.
  */
-function getValidUserRecord(serverResponse: any) {
+function getValidUserRecord(serverResponse: any): UserRecord {
   return new UserRecord(serverResponse.users[0]);
 }
 
@@ -140,13 +140,13 @@ function getDecodedIdToken(uid: string, authTime: Date, tenantId?: string): Deco
   return {
     iss: 'https://securetoken.google.com/project123456789',
     aud: 'project123456789',
-    auth_time: Math.floor(authTime.getTime() / 1000),
+    auth_time: Math.floor(authTime.getTime() / 1000), // eslint-disable-line @typescript-eslint/camelcase
     sub: uid,
     iat: Math.floor(authTime.getTime() / 1000),
     exp: Math.floor(authTime.getTime() / 1000 + 3600),
     firebase: {
       identities: {},
-      sign_in_provider: 'custom',
+      sign_in_provider: 'custom', // eslint-disable-line @typescript-eslint/camelcase
       tenant: tenantId,
     },
   };
@@ -165,13 +165,13 @@ function getDecodedSessionCookie(uid: string, authTime: Date, tenantId?: string)
   return {
     iss: 'https://session.firebase.google.com/project123456789',
     aud: 'project123456789',
-    auth_time: Math.floor(authTime.getTime() / 1000),
+    auth_time: Math.floor(authTime.getTime() / 1000), // eslint-disable-line @typescript-eslint/camelcase
     sub: uid,
     iat: Math.floor(authTime.getTime() / 1000),
     exp: Math.floor(authTime.getTime() / 1000 + 3600),
     firebase: {
       identities: {},
-      sign_in_provider: 'custom',
+      sign_in_provider: 'custom', // eslint-disable-line @typescript-eslint/camelcase
       tenant: tenantId,
     },
   };
diff --git a/test/unit/auth/credential.spec.ts b/test/unit/auth/credential.spec.ts
index 368d983f0c..881dcb7525 100644
--- a/test/unit/auth/credential.spec.ts
+++ b/test/unit/auth/credential.spec.ts
@@ -42,6 +42,8 @@ chai.should();
 chai.use(sinonChai);
 chai.use(chaiAsPromised);
 
+/* eslint-disable @typescript-eslint/camelcase */
+
 const expect = chai.expect;
 
 const GCLOUD_CREDENTIAL_SUFFIX = 'gcloud/application_default_credentials.json';
diff --git a/test/unit/auth/token-generator.spec.ts b/test/unit/auth/token-generator.spec.ts
index 6e28929014..3a6dbe4df4 100644
--- a/test/unit/auth/token-generator.spec.ts
+++ b/test/unit/auth/token-generator.spec.ts
@@ -84,6 +84,7 @@ describe('CryptoSigner', () => {
       const payload = Buffer.from('test');
       const cert = new ServiceAccountCredential(mocks.certificateObject);
 
+      // eslint-disable-next-line @typescript-eslint/no-var-requires
       const crypto = require('crypto');
       const rsa = crypto.createSign('RSA-SHA256');
       rsa.update(payload);
@@ -400,6 +401,7 @@ describe('FirebaseTokenGenerator', () => {
             };
 
             if (tokenGenerator.tenantId) {
+              // eslint-disable-next-line @typescript-eslint/camelcase
               expected.tenant_id = tokenGenerator.tenantId;
             }
 
@@ -428,6 +430,7 @@ describe('FirebaseTokenGenerator', () => {
             };
 
             if (tokenGenerator.tenantId) {
+              // eslint-disable-next-line @typescript-eslint/camelcase
               expected.tenant_id = tokenGenerator.tenantId;
             }
 
diff --git a/test/unit/auth/token-verifier.spec.ts b/test/unit/auth/token-verifier.spec.ts
index 8de2ca54a3..bf95f96380 100644
--- a/test/unit/auth/token-verifier.spec.ts
+++ b/test/unit/auth/token-verifier.spec.ts
@@ -88,7 +88,7 @@ function mockFetchPublicKeysWithErrorResponse(): nock.Scope {
     .get('/robot/v1/metadata/x509/securetoken@system.gserviceaccount.com')
     .reply(200, {
       error: 'message',
-      error_description: 'description',
+      error_description: 'description', // eslint-disable-line @typescript-eslint/camelcase
     });
 }
 
diff --git a/test/unit/firebase-app.spec.ts b/test/unit/firebase-app.spec.ts
index 001d959bcf..d28cdd166d 100644
--- a/test/unit/firebase-app.spec.ts
+++ b/test/unit/firebase-app.spec.ts
@@ -70,8 +70,8 @@ describe('FirebaseApp', () => {
 
   beforeEach(() => {
     getTokenStub = sinon.stub(ServiceAccountCredential.prototype, 'getAccessToken').resolves({
-      access_token: 'mock-access-token',
-      expires_in: 3600,
+      access_token: 'mock-access-token', // eslint-disable-line @typescript-eslint/camelcase
+      expires_in: 3600, // eslint-disable-line @typescript-eslint/camelcase
     });
 
     clock = sinon.useFakeTimers(1000);
@@ -667,8 +667,8 @@ describe('FirebaseApp', () => {
 
     it('returns a valid token given a well-formed custom credential implementation', () => {
       const oracle: GoogleOAuthAccessToken = {
-        access_token: 'This is a custom token',
-        expires_in: ONE_HOUR_IN_SECONDS,
+        access_token: 'This is a custom token', // eslint-disable-line @typescript-eslint/camelcase
+        expires_in: ONE_HOUR_IN_SECONDS, // eslint-disable-line @typescript-eslint/camelcase
       };
       const credential = {
         getAccessToken: () => Promise.resolve(oracle),
@@ -761,8 +761,8 @@ describe('FirebaseApp', () => {
         // Restore the stubbed getAccessToken() method.
         getTokenStub.restore();
         getTokenStub = sinon.stub(ServiceAccountCredential.prototype, 'getAccessToken').resolves({
-          access_token: 'mock-access-token',
-          expires_in: 3600,
+          access_token: 'mock-access-token', // eslint-disable-line @typescript-eslint/camelcase
+          expires_in: 3600, // eslint-disable-line @typescript-eslint/camelcase
         });
 
         return mockApp.INTERNAL.getToken().then((token2) => {
@@ -914,8 +914,8 @@ describe('FirebaseApp', () => {
       getTokenStub.restore();
       expect(mockApp.options.credential).to.exist;
       getTokenStub = sinon.stub(mockApp.options.credential!, 'getAccessToken').resolves({
-        access_token: utils.generateRandomAccessToken(),
-        expires_in: 3 * 60 + 10,
+        access_token: utils.generateRandomAccessToken(), // eslint-disable-line @typescript-eslint/camelcase
+        expires_in: 3 * 60 + 10, // eslint-disable-line @typescript-eslint/camelcase
       });
       // Expect the call count to initially be zero.
       expect(getTokenStub.callCount).to.equal(0);
diff --git a/test/unit/firebase.spec.ts b/test/unit/firebase.spec.ts
index bdbd4d787a..4471ed630e 100644
--- a/test/unit/firebase.spec.ts
+++ b/test/unit/firebase.spec.ts
@@ -40,8 +40,8 @@ describe('Firebase', () => {
 
   before(() => {
     getTokenStub = sinon.stub(ServiceAccountCredential.prototype, 'getAccessToken').resolves({
-      access_token: 'mock-access-token',
-      expires_in: 3600,
+      access_token: 'mock-access-token', // eslint-disable-line @typescript-eslint/camelcase
+      expires_in: 3600, // eslint-disable-line @typescript-eslint/camelcase
     });
   });
 
@@ -150,8 +150,8 @@ describe('Firebase', () => {
       getTokenStub.restore();
       getTokenStub = sinon.stub(RefreshTokenCredential.prototype, 'getAccessToken')
         .resolves({
-          access_token: 'mock-access-token',
-          expires_in: 3600,
+          access_token: 'mock-access-token', // eslint-disable-line @typescript-eslint/camelcase
+          expires_in: 3600, // eslint-disable-line @typescript-eslint/camelcase
         });
       firebaseAdmin.initializeApp({
         credential: firebaseAdmin.credential.refreshToken(mocks.refreshToken),
diff --git a/test/unit/firestore/firestore.spec.ts b/test/unit/firestore/firestore.spec.ts
index df72549b40..482211ffa0 100644
--- a/test/unit/firestore/firestore.spec.ts
+++ b/test/unit/firestore/firestore.spec.ts
@@ -38,6 +38,7 @@ describe('Firestore', () => {
     + 'credentials. Must initialize the SDK with a certificate credential or application default '
     + 'credentials to use Cloud Firestore API.';
 
+  // eslint-disable-next-line @typescript-eslint/no-var-requires
   const { version: firebaseVersion } = require('../../../package.json');
   const defaultCredentialApps = [
     {
diff --git a/test/unit/messaging/batch-requests.spec.ts b/test/unit/messaging/batch-requests.spec.ts
index 9bc11532a0..bcfee5ef74 100644
--- a/test/unit/messaging/batch-requests.spec.ts
+++ b/test/unit/messaging/batch-requests.spec.ts
@@ -33,6 +33,7 @@ chai.use(chaiAsPromised);
 const expect = chai.expect;
 
 function parseHttpRequest(text: string | Buffer): any {
+  // eslint-disable-next-line @typescript-eslint/no-var-requires
   const httpMessageParser = require('http-message-parser');
   return httpMessageParser(text);
 }
@@ -241,7 +242,7 @@ describe('BatchRequestClient', () => {
     });
   });
 
-  function checkOutgoingRequest(stub: sinon.SinonStub, requests: SubRequest[]) {
+  function checkOutgoingRequest(stub: sinon.SinonStub, requests: SubRequest[]): void {
     expect(stub).to.have.been.calledOnce;
     const args: HttpRequestConfig = stub.getCall(0).args[0];
     expect(args.method).to.equal('POST');
diff --git a/test/unit/messaging/messaging.spec.ts b/test/unit/messaging/messaging.spec.ts
index 286f5d2702..9bd41b374e 100644
--- a/test/unit/messaging/messaging.spec.ts
+++ b/test/unit/messaging/messaging.spec.ts
@@ -158,6 +158,8 @@ function mockErrorResponse(
     });
 }
 
+/* eslint-disable @typescript-eslint/camelcase */
+
 function mockSendToDeviceStringRequest(mockFailure = false): nock.Scope {
   let deviceResult: object = { message_id: `0:${ mocks.messaging.messageId }` };
   if (mockFailure) {
@@ -299,7 +301,7 @@ function mockTopicSubscriptionRequestWithError(
     });
 }
 
-function disableRetries(messaging: Messaging) {
+function disableRetries(messaging: Messaging): void {
   (messaging as any).messagingRequestHandler.httpClient.retry = null;
 }
 
@@ -561,13 +563,13 @@ describe('Messaging', () => {
   describe('sendAll()', () => {
     const validMessage: Message = {token: 'a'};
 
-    function checkSendResponseSuccess(response: SendResponse, messageId: string) {
+    function checkSendResponseSuccess(response: SendResponse, messageId: string): void {
       expect(response.success).to.be.true;
       expect(response.messageId).to.equal(messageId);
       expect(response.error).to.be.undefined;
     }
 
-    function checkSendResponseFailure(response: SendResponse, code: string, msg?: string) {
+    function checkSendResponseFailure(response: SendResponse, code: string, msg?: string): void {
       expect(response.success).to.be.false;
       expect(response.messageId).to.be.undefined;
       expect(response.error).to.have.property('code', code);
@@ -1108,13 +1110,13 @@ describe('Messaging', () => {
       ).should.eventually.be.rejected.and.have.property('code', 'app/invalid-credential');
     });
 
-    function checkSendResponseSuccess(response: SendResponse, messageId: string) {
+    function checkSendResponseSuccess(response: SendResponse, messageId: string): void {
       expect(response.success).to.be.true;
       expect(response.messageId).to.equal(messageId);
       expect(response.error).to.be.undefined;
     }
 
-    function checkSendResponseFailure(response: SendResponse, code: string, msg?: string) {
+    function checkSendResponseFailure(response: SendResponse, code: string, msg?: string): void {
       expect(response.success).to.be.false;
       expect(response.messageId).to.be.undefined;
       expect(response.error).to.have.property('code', code);
@@ -3596,7 +3598,7 @@ describe('Messaging', () => {
     });
   });
 
-  function tokenSubscriptionTests(methodName: string) {
+  function tokenSubscriptionTests(methodName: string): void {
     const invalidRegistrationTokensArgumentError = 'Registration token(s) provided to ' +
       `${methodName}() must be a non-empty string or a non-empty array`;
 
diff --git a/test/unit/project-management/android-app.spec.ts b/test/unit/project-management/android-app.spec.ts
index 2fed6622ed..d38c2600b7 100644
--- a/test/unit/project-management/android-app.spec.ts
+++ b/test/unit/project-management/android-app.spec.ts
@@ -132,7 +132,7 @@ describe('AndroidApp', () => {
           .should.eventually.be.rejected
           .and.have.property(
             'message',
-            `getMetadata()\'s responseData.${requiredField} must be a non-empty string. `
+            `getMetadata()'s responseData.${requiredField} must be a non-empty string. `
                     + `Response data: ${JSON.stringify(partialApiResponse, null, 2)}`);
       });
     });
@@ -250,7 +250,7 @@ describe('AndroidApp', () => {
           .should.eventually.be.rejected
           .and.have.property(
             'message',
-            `getShaCertificates()\'s responseData.certificates[].${requiredField} must be a `
+            `getShaCertificates()'s responseData.certificates[].${requiredField} must be a `
                     + 'non-empty string. Response data: '
                     + JSON.stringify(partialApiResponse, null, 2));
       });
@@ -357,7 +357,7 @@ describe('AndroidApp', () => {
         .should.eventually.be.rejected
         .and.have.property(
           'message',
-          `getConfig()\'s responseData.configFileContents must be a base64 string. `
+          `getConfig()'s responseData.configFileContents must be a base64 string. `
                   + `Response data: ${JSON.stringify(apiResponse, null, 2)}`);
     });
 
diff --git a/test/unit/project-management/ios-app.spec.ts b/test/unit/project-management/ios-app.spec.ts
index 3f84e3713b..ec300ea554 100644
--- a/test/unit/project-management/ios-app.spec.ts
+++ b/test/unit/project-management/ios-app.spec.ts
@@ -131,7 +131,7 @@ describe('IosApp', () => {
           .should.eventually.be.rejected
           .and.have.property(
             'message',
-            `getMetadata()\'s responseData.${requiredField} must be a non-empty string. `
+            `getMetadata()'s responseData.${requiredField} must be a non-empty string. `
                     + `Response data: ${JSON.stringify(partialApiResponse, null, 2)}`);
       });
     });
@@ -204,7 +204,7 @@ describe('IosApp', () => {
         .should.eventually.be.rejected
         .and.have.property(
           'message',
-          `getConfig()\'s responseData.configFileContents must be a base64 string. `
+          `getConfig()'s responseData.configFileContents must be a base64 string. `
                   + `Response data: ${JSON.stringify(apiResponse, null, 2)}`);
     });
 
diff --git a/test/unit/project-management/project-management-api-request.spec.ts b/test/unit/project-management/project-management-api-request.spec.ts
index 59d91b69f5..f2978b4a34 100644
--- a/test/unit/project-management/project-management-api-request.spec.ts
+++ b/test/unit/project-management/project-management-api-request.spec.ts
@@ -84,7 +84,7 @@ describe('ProjectManagementRequestHandler', () => {
     return mockApp.delete();
   });
 
-  function testHttpErrors(callback: () => Promise<any>) {
+  function testHttpErrors(callback: () => Promise<any>): void {
     const errorCodeMap: any = {
       400: 'project-management/invalid-argument',
       401: 'project-management/authentication-error',
@@ -94,7 +94,7 @@ describe('ProjectManagementRequestHandler', () => {
       503: 'project-management/service-unavailable',
     };
     Object.keys(errorCodeMap).forEach((errorCode) => {
-      if (!errorCodeMap.hasOwnProperty(errorCode)) {
+      if (!Object.prototype.hasOwnProperty.call(errorCodeMap, errorCode)) {
         return;
       }
       it(`should throw for HTTP ${errorCode} errors`, () => {
diff --git a/test/unit/utils.ts b/test/unit/utils.ts
index 6f6dac1a1a..12bc260b65 100644
--- a/test/unit/utils.ts
+++ b/test/unit/utils.ts
@@ -29,7 +29,7 @@ import { HttpError, HttpResponse } from '../../src/utils/api-request';
  * @param {object} options The options for the FirebaseApp instance to create.
  * @return {FirebaseApp} A new FirebaseApp instance with the provided options.
  */
-export function createAppWithOptions(options: object) {
+export function createAppWithOptions(options: object): FirebaseApp {
   const mockFirebaseNamespaceInternals = new FirebaseNamespace().INTERNAL;
   return new FirebaseApp(options as FirebaseAppOptions, mocks.appName, mockFirebaseNamespaceInternals);
 }
diff --git a/test/unit/utils/api-request.spec.ts b/test/unit/utils/api-request.spec.ts
index 7a04df15a6..3052d01e81 100644
--- a/test/unit/utils/api-request.spec.ts
+++ b/test/unit/utils/api-request.spec.ts
@@ -66,7 +66,7 @@ function mockRequestWithHttpError(
   statusCode = 400,
   responseContentType = 'application/json',
   response: any = mockErrorResponse,
-) {
+): nock.Scope {
   if (responseContentType === 'text/html') {
     response = mockTextErrorResponse;
   }
@@ -86,7 +86,7 @@ function mockRequestWithHttpError(
  *
  * @return {Object} A nock response object.
  */
-function mockRequestWithError(err: any) {
+function mockRequestWithError(err: any): nock.Scope {
   return nock('https://' + mockHost)
     .get(mockPath)
     .replyWithError(err);
@@ -346,6 +346,8 @@ describe('HttpClient', () => {
     mockedRequests.push(scope);
     const client = new HttpClient();
     const httpAgent = new Agent();
+
+    // eslint-disable-next-line @typescript-eslint/no-var-requires
     const https = require('https');
     transportSpy = sinon.spy(https, 'request');
     return client.send({
@@ -1224,6 +1226,8 @@ describe('AuthorizedHttpClient', () => {
     beforeEach(() => {
       const options = mockApp.options;
       options.httpAgent = new Agent();
+
+      // eslint-disable-next-line @typescript-eslint/no-var-requires
       const https = require('https');
       transportSpy = sinon.spy(https, 'request');
       mockAppWithAgent = mocks.appWithOptions(options);
diff --git a/test/unit/utils/index.spec.ts b/test/unit/utils/index.spec.ts
index 8413a8e979..705afab3a9 100755
--- a/test/unit/utils/index.spec.ts
+++ b/test/unit/utils/index.spec.ts
@@ -48,7 +48,7 @@ describe('addReadonlyGetter()', () => {
 
     expect(() => {
       obj.foo = false;
-    }).to.throw(/Cannot assign to read only property \'foo\' of/);
+    }).to.throw(/Cannot assign to read only property 'foo' of/);
   });
 
   it('should make the new property enumerable', () => {