diff --git a/package.json b/package.json
index 471782b6..e5f7e1e0 100644
--- a/package.json
+++ b/package.json
@@ -17,9 +17,10 @@
     "lint-staged": "npx lint-staged",
     "clean": "npx rimraf dist && rimraf out-tsc",
     "tools:download-schemas": "npx ts-node --project ./tools/tsconfig.json ./tools/download-schemas.ts",
+    "tools:generate-merged_json": "npx ts-node --project ./tools/tsconfig.json ./tools/generate-merged_json.ts",
     "tools:generate-definitions": "npx ts-node --project ./tools/tsconfig.json ./tools/generate-definitions.ts",
     "tools:generate-builders": "npx ts-node --project ./tools/tsconfig.json ./tools/generate-builders.ts",
-    "update-code-base": "npm run tools:download-schemas && npm run tools:generate-definitions && npm run tools:generate-builders && npm run format && npm run test",
+    "update-code-base": "npm run tools:download-schemas && tools:generate-merged_json && npm run tools:generate-definitions && npm run tools:generate-builders && npm run format && npm run test",
     "format": "npx prettier --write \"**/*.ts\"",
     "lint": "npx eslint . --ext .ts && npx prettier --check \"**/*.ts\"",
     "pretest": "npx rimraf out-tsc",
diff --git a/tools/download-schemas.ts b/tools/download-schemas.ts
index 15a3fad3..cf3f430e 100644
--- a/tools/download-schemas.ts
+++ b/tools/download-schemas.ts
@@ -14,18 +14,15 @@
  * limitations under the License.
  */
 import $RefParser from '@apidevtools/json-schema-ref-parser';
-import { promises as fsPromises } from 'fs';
+import {promises as fsPromises} from 'fs';
 import * as path from 'path';
-import { URL } from 'url';
-import yargs from 'yargs';
-import { schemaVersion } from '../package.json';
-import { mergeDefinitions, mergeSchemas, reset } from './utils';
+import {URL} from 'url';
+import {schemaDir, reset, schemaUrl} from './utils';
 
 const { writeFile, mkdir } = fsPromises;
 
 /**
  * Downloads the given schema (and referenced sub-schema) and save them to disk
- * A merged schema is also saved as `__merged.json`
  * @param schemaUrl {string} The URL to download the schema from
  * @param destDir {string} The destination path to save the schema to
  * @returns {void}
@@ -49,21 +46,11 @@ const download = async (schemaUrl: URL, destDir: string): Promise<void> => {
         await writeFile(path.resolve(destDir, externalSchemaFileName), JSON.stringify(externalSchema, null, 2));
       }
     });
-    const known$Refs = new Map<string, string>();
-    await mergeDefinitions($refParser, externalSchemas, known$Refs);
-    mergeSchemas($refParser, known$Refs, $refParser.schema, '#/');
-    await writeFile(path.resolve(destDir, '__merged.json'), JSON.stringify($refParser.schema, null, 2));
     return Promise.resolve();
   } catch (ex) {
     return Promise.reject(ex);
   }
 };
 
-const argv = yargs(process.argv.slice(2)).argv;
-const schemaUrl: URL = new URL(
-  (argv.url as string) ||
-    `https://raw.githubusercontent.com/serverlessworkflow/specification/${schemaVersion}.x/schema/workflow.json`
-);
-const destDir = path.resolve(process.cwd(), 'src/lib/schema');
 
-download(schemaUrl, destDir).then(console.log.bind(console)).catch(console.error.bind(console));
+download(schemaUrl, schemaDir).then(console.log.bind(console)).catch(console.error.bind(console));
diff --git a/tools/generate-merged_json.ts b/tools/generate-merged_json.ts
new file mode 100644
index 00000000..9f494014
--- /dev/null
+++ b/tools/generate-merged_json.ts
@@ -0,0 +1,48 @@
+/*
+ * Copyright 2021-Present The Serverless Workflow Specification Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+import $RefParser from '@apidevtools/json-schema-ref-parser';
+import { promises as fsPromises } from 'fs';
+import * as path from 'path';
+import { URL } from 'url';
+import {schemaDir, mergeDefinitions, mergeSchemas, schemaUrl} from './utils';
+
+const { writeFile} = fsPromises;
+
+/**
+ * Generate a merged schema `__merged.json` from schemas in schemas directory
+ * @param schemaUrl {string} The URL to download the schema from //TODO this does not like right, revisit mergeDefinitions
+ * @param destDir {string} The destination path to save the schema to
+ * @returns {void}
+ */
+const execute = async (schemaUrl: URL, destDir: string): Promise<void> => {
+  try {
+    const $refParser = new $RefParser();
+    await $refParser.resolve(schemaUrl.href);
+    const externalSchemas = $refParser.$refs
+      .paths()
+      .filter((p, index, arr) => arr.indexOf(p) === index && p !== schemaUrl.href);
+
+    const known$Refs = new Map<string, string>();
+    await mergeDefinitions($refParser, externalSchemas, known$Refs);
+    mergeSchemas($refParser, known$Refs, $refParser.schema, '#/');
+    await writeFile(path.resolve(destDir, '__merged.json'), JSON.stringify($refParser.schema, null, 2));
+    return Promise.resolve();
+  } catch (ex) {
+    return Promise.reject(ex);
+  }
+};
+
+execute(schemaUrl, schemaDir).then(console.log.bind(console)).catch(console.error.bind(console));
diff --git a/tools/utils.ts b/tools/utils.ts
index af6abdf0..d287e5ad 100644
--- a/tools/utils.ts
+++ b/tools/utils.ts
@@ -19,6 +19,9 @@ import { promises as fsPromises } from 'fs';
 import * as path from 'path';
 import rimraf from 'rimraf';
 import { readMeDisclaimer } from './consts';
+import {URL} from "url";
+import yargs from "yargs";
+import {schemaVersion} from "../package.json";
 
 const { writeFile, mkdir } = fsPromises;
 
@@ -175,3 +178,14 @@ export const reset = async (destDir: string) =>
   rimrafP(destDir)
     .then(() => mkdir(destDir, { recursive: true }))
     .then(() => writeFile(path.resolve(destDir, 'README.md'), readMeDisclaimer));
+
+
+/** Schemas directory */
+export const schemaDir = path.resolve(process.cwd(), 'src/lib/schema');
+
+
+/** The URL to download the schema from */
+export const schemaUrl: URL = new URL(
+    (yargs(process.argv.slice(2)).argv.url as string) ||
+    `https://raw.githubusercontent.com/serverlessworkflow/specification/${schemaVersion}.x/schema/workflow.json`
+);