diff --git a/server/darwin/rescript-editor-support.exe b/server/darwin/rescript-editor-support.exe
new file mode 100755
index 000000000..da90bc08a
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diff --git a/server/linux/rescript-editor-support.exe b/server/linux/rescript-editor-support.exe
new file mode 100755
index 000000000..b07bd6139
Binary files /dev/null and b/server/linux/rescript-editor-support.exe differ
diff --git a/server/src/RescriptEditorSupport.ts b/server/src/RescriptEditorSupport.ts
new file mode 100644
index 000000000..44e550e84
--- /dev/null
+++ b/server/src/RescriptEditorSupport.ts
@@ -0,0 +1,90 @@
+import { fileURLToPath } from "url";
+import { RequestMessage } from "vscode-languageserver";
+import * as utils from "./utils";
+import * as path from "path";
+import { exec } from "child_process";
+import * as tmp from "tmp";
+import fs from "fs";
+
+let binaryPath = path.join(
+  path.dirname(__dirname),
+  process.platform,
+  "rescript-editor-support.exe"
+);
+
+export let binaryExists = fs.existsSync(binaryPath);
+
+let findExecutable = (uri: string) => {
+  let filePath = fileURLToPath(uri);
+  let projectRootPath = utils.findProjectRootOfFile(filePath);
+  if (projectRootPath == null || !binaryExists) {
+    return null;
+  } else {
+    return { binaryPath, filePath, cwd: projectRootPath };
+  }
+};
+
+export function runDumpCommand(
+  msg: RequestMessage,
+  onResult: (
+    result: { hover?: string; definition?: { uri?: string; range: any } } | null
+  ) => void
+) {
+  let executable = findExecutable(msg.params.textDocument.uri);
+  if (executable == null) {
+    onResult(null);
+  } else {
+    let command =
+      executable.binaryPath +
+      " dump " +
+      executable.filePath +
+      ":" +
+      msg.params.position.line +
+      ":" +
+      msg.params.position.character;
+    exec(command, { cwd: executable.cwd }, function (_error, stdout, _stderr) {
+      let result = JSON.parse(stdout);
+      if (result && result[0]) {
+        onResult(result[0]);
+      } else {
+        onResult(null);
+      }
+    });
+  }
+}
+
+export function runCompletionCommand(
+  msg: RequestMessage,
+  code: string,
+  onResult: (result: [{ label: string }] | null) => void
+) {
+  let executable = findExecutable(msg.params.textDocument.uri);
+  if (executable == null) {
+    onResult(null);
+  } else {
+    let tmpobj = tmp.fileSync();
+    let tmpname = tmpobj.name;
+    fs.writeFileSync(tmpname, code, { encoding: "utf-8" });
+
+    let command =
+      executable.binaryPath +
+      " complete " +
+      executable.filePath +
+      ":" +
+      msg.params.position.line +
+      ":" +
+      msg.params.position.character +
+      " " +
+      tmpname;
+
+    exec(command, { cwd: executable.cwd }, function (_error, stdout, _stderr) {
+      tmpobj.removeCallback();
+      let result = JSON.parse(stdout);
+      if (result && result[0]) {
+        onResult(result);
+      } else {
+        onResult(null);
+      }
+    });
+  }
+}
diff --git a/server/src/server.ts b/server/src/server.ts
index fcb873a75..527c64129 100644
--- a/server/src/server.ts
+++ b/server/src/server.ts
@@ -20,6 +20,11 @@ import * as chokidar from "chokidar";
 import { assert } from "console";
 import { fileURLToPath } from "url";
 import { ChildProcess } from "child_process";
+import {
+  binaryExists,
+  runDumpCommand,
+  runCompletionCommand,
+} from "./RescriptEditorSupport";
 
 // https://microsoft.github.io/language-server-protocol/specification#initialize
 // According to the spec, there could be requests before the 'initialize' request. Link in comment tells how to handle them.
@@ -268,8 +273,11 @@ process.on("message", (msg: m.Message) => {
           // TODO: incremental sync?
           textDocumentSync: v.TextDocumentSyncKind.Full,
           documentFormattingProvider: true,
-          hoverProvider: true,
-          definitionProvider: true,
+          hoverProvider: binaryExists,
+          definitionProvider: binaryExists,
+          completionProvider: binaryExists
+            ? { triggerCharacters: ["."] }
+            : undefined,
         },
       };
       let response: m.ResponseMessage = {
@@ -313,32 +321,68 @@ process.on("message", (msg: m.Message) => {
         process.send!(response);
       }
     } else if (msg.method === p.HoverRequest.method) {
-      let dummyHoverResponse: m.ResponseMessage = {
+      let emptyHoverResponse: m.ResponseMessage = {
         jsonrpc: c.jsonrpcVersion,
         id: msg.id,
         // type result = Hover | null
         // type Hover = {contents: MarkedString | MarkedString[] | MarkupContent, range?: Range}
-        result: { contents: "Time to go for a 20k run!" },
+        result: null,
       };
-
-      process.send!(dummyHoverResponse);
+      runDumpCommand(msg, (result) => {
+        if (result && result.hover) {
+          let hoverResponse: m.ResponseMessage = {
+            ...emptyHoverResponse,
+            result: {
+              contents: result.hover,
+            },
+          };
+          process.send!(hoverResponse);
+        } else {
+          process.send!(emptyHoverResponse);
+        }
+      });
     } else if (msg.method === p.DefinitionRequest.method) {
       // https://microsoft.github.io/language-server-protocol/specifications/specification-current/#textDocument_definition
-      let dummyDefinitionResponse: m.ResponseMessage = {
+      let emptyDefinitionResponse: m.ResponseMessage = {
         jsonrpc: c.jsonrpcVersion,
         id: msg.id,
         // result should be: Location | Array<Location> | Array<LocationLink> | null
-        result: {
-          uri: msg.params.textDocument.uri,
-          range: {
-            start: { line: 2, character: 4 },
-            end: { line: 2, character: 12 },
-          },
-        },
+        result: null,
         // error: code and message set in case an exception happens during the definition request.
       };
 
-      process.send!(dummyDefinitionResponse);
+      runDumpCommand(msg, (result) => {
+        if (result && result.definition) {
+          let definitionResponse: m.ResponseMessage = {
+            ...emptyDefinitionResponse,
+            result: {
+              uri: result.definition.uri || msg.params.textDocument.uri,
+              range: result.definition.range,
+            },
+          };
+          process.send!(definitionResponse);
+        } else {
+          process.send!(emptyDefinitionResponse);
+        }
+      });
+    } else if (msg.method === p.CompletionRequest.method) {
+      let emptyCompletionResponse: m.ResponseMessage = {
+        jsonrpc: c.jsonrpcVersion,
+        id: msg.id,
+        result: null,
+      };
+      let code = getOpenedFileContent(msg.params.textDocument.uri);
+      runCompletionCommand(msg, code, (result) => {
+        if (result) {
+          let definitionResponse: m.ResponseMessage = {
+            ...emptyCompletionResponse,
+            result: result,
+          };
+          process.send!(definitionResponse);
+        } else {
+          process.send!(emptyCompletionResponse);
+        }
+      });
     } else if (msg.method === p.DocumentFormattingRequest.method) {
       // technically, a formatting failure should reply with the error. Sadly
       // the LSP alert box for these error replies sucks (e.g. doesn't actually
diff --git a/server/win32/rescript-editor-support.exe b/server/win32/rescript-editor-support.exe
new file mode 100755
index 000000000..3dd8a8cd5
Binary files /dev/null and b/server/win32/rescript-editor-support.exe differ