diff --git a/package.json b/package.json
index 6a914ae..78c6db3 100644
--- a/package.json
+++ b/package.json
@@ -54,19 +54,22 @@
     "lint": "eslint src --ext ts"
   },
   "devDependencies": {
-    "@types/vscode": "^1.72.0",
     "@types/glob": "^8.0.0",
     "@types/mocha": "^10.0.0",
     "@types/node": "16.x",
+    "@types/vscode": "^1.72.0",
     "@typescript-eslint/eslint-plugin": "^5.38.1",
     "@typescript-eslint/parser": "^5.38.1",
+    "@vscode/test-electron": "^2.1.5",
     "eslint": "^8.24.0",
     "glob": "^8.0.3",
     "mocha": "^10.0.0",
-    "typescript": "^4.8.4",
     "ts-loader": "^9.4.1",
+    "typescript": "^4.8.4",
     "webpack": "^5.74.0",
-    "webpack-cli": "^4.10.0",
-    "@vscode/test-electron": "^2.1.5"
+    "webpack-cli": "^4.10.0"
+  },
+  "dependencies": {
+    "vscode-languageclient": "^8.0.2"
   }
 }
diff --git a/src/completion.ts b/src/completion.ts
deleted file mode 100644
index 3e50e94..0000000
--- a/src/completion.ts
+++ /dev/null
@@ -1,34 +0,0 @@
-// completion provider for feakin
-
-import * as vscode from "vscode";
-import * as fs from "fs";
-
-export class FklCompletionItemProvider
-  implements vscode.CompletionItemProvider
-{
-  output: vscode.OutputChannel;
-  constructor(output: vscode.OutputChannel) {
-    this.output = output;
-  }
-
-  public async provideCompletionItems(
-    document: vscode.TextDocument,
-    position: vscode.Position,
-    token: vscode.CancellationToken
-  ): Promise<vscode.CompletionItem[]> {
-    this.output.appendLine("provideCompletionItems:");
-    this.output.appendLine("  document: " + document.fileName);
-    this.output.appendLine(
-      "  position: " + position.line + ", " + position.character
-    );
-
-    return [
-      {
-        label: "hello",
-        kind: vscode.CompletionItemKind.Text,
-      },
-    ];
-
-    return [];
-  }
-}
diff --git a/src/extension.ts b/src/extension.ts
index d8b1134..6bcbd3c 100644
--- a/src/extension.ts
+++ b/src/extension.ts
@@ -1,33 +1,62 @@
+import * as path from "node:path";
+
 // The module 'vscode' contains the VS Code extensibility API
 // Import the module and reference it with the alias vscode in your code below
 import * as vscode from "vscode";
-
-import { FklCompletionItemProvider } from "./completion";
+import {
+  LanguageClient,
+  LanguageClientOptions,
+  ServerOptions,
+  TransportKind,
+} from "vscode-languageclient/node";
 
 let output: vscode.OutputChannel;
 
-// This method is called when your extension is activated
-// Your extension is activated the very first time the command is executed
-export function activate(context: vscode.ExtensionContext) {
-  // The command has been defined in the package.json file
-  // Now provide the implementation of the command with registerCommand
-  // The commandId parameter must match the command field in package.json
+export async function activate(context: vscode.ExtensionContext) {
   console.log("Congratulations, your extension 'fkl' is now active!");
 
   output = vscode.window.createOutputChannel("Fkl", "fkl");
   context.subscriptions.push(output);
   output.show();
 
-  console.log("Fkl: activate" + context.extensionPath + " " + output);
+  let client;
+
+  // TODO: download fkl-lsp from github
+  let exe = path.resolve(__dirname, "../../fklang/target/debug/fkl-lsp.exe");
+
+  // check if exe exists
+  try {
+    await vscode.workspace.fs.stat(vscode.Uri.file(exe));
+  } catch (error) {
+    output.appendLine("fkl-lsp not found");
+    return;
+  }
+
+  const serverOptions: ServerOptions = {
+    run: { command: exe, transport: TransportKind.stdio },
+    debug: {
+      command: exe,
+      transport: TransportKind.stdio,
+    },
+  };
+
+  // Options to control the language client
+  let clientOptions: LanguageClientOptions = {
+    // Register the server for plain text documents
+    documentSelector: [{ scheme: "file", language: "fkl" }],
+    outputChannel: output,
+    progressOnInitialization: true,
+    traceOutputChannel: output,
+    synchronize: {
+      // Notify the server about file changes to '.clientrc files contained in the workspace
+      fileEvents: vscode.workspace.createFileSystemWatcher("**/*.fkl"),
+    },
+  };
+
+  client = new LanguageClient("fkl-lsp-client", serverOptions, clientOptions);
+  client.start();
 
-  context.subscriptions.push(
-    vscode.languages.registerCompletionItemProvider(
-      { pattern: "**/*.fkl", scheme: "file" },
-      new FklCompletionItemProvider(output),
-      ".",
-      " "
-    )
-  );
+  context.subscriptions.push(client);
 }
 
 // This method is called when your extension is deactivated
diff --git a/test_data/a.fkl b/test_data/a.fkl
index 032e095..58ccafe 100644
--- a/test_data/a.fkl
+++ b/test_data/a.fkl
@@ -10,6 +10,7 @@ Context Reservation {
 
 Aggregate Reservation {
   Entity Ticket, Reservation;
+  
 }
 
 Entity Reservation  {
diff --git a/yarn.lock b/yarn.lock
index 2380fa1..b940384 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1681,7 +1681,7 @@ schema-utils@^3.1.0, schema-utils@^3.1.1:
     ajv "^6.12.5"
     ajv-keywords "^3.5.2"
 
-semver@^7.3.4, semver@^7.3.7:
+semver@^7.3.4, semver@^7.3.5, semver@^7.3.7:
   version "7.3.8"
   resolved "https://registry.yarnpkg.com/semver/-/semver-7.3.8.tgz#07a78feafb3f7b32347d725e33de7e2a2df67798"
   integrity sha512-NB1ctGL5rlHrPJtFDVIVzTyQylMLu9N9VICA6HSFJo8MCGVTMW6gfpicwKmmK/dAjTOrqu5l63JJOpDSrAis3A==
@@ -1902,6 +1902,33 @@ util-deprecate@~1.0.1:
   resolved "https://registry.yarnpkg.com/util-deprecate/-/util-deprecate-1.0.2.tgz#450d4dc9fa70de732762fbd2d4a28981419a0ccf"
   integrity sha512-EPD5q1uXyFxJpCrLnCc1nHnq3gOa6DZBocAIiI2TaSCA7VCJ1UJDMagCzIkXNsUYfD1daK//LTEQ8xiIbrHtcw==
 
+vscode-jsonrpc@8.0.2:
+  version "8.0.2"
+  resolved "https://registry.yarnpkg.com/vscode-jsonrpc/-/vscode-jsonrpc-8.0.2.tgz#f239ed2cd6004021b6550af9fd9d3e47eee3cac9"
+  integrity sha512-RY7HwI/ydoC1Wwg4gJ3y6LpU9FJRZAUnTYMXthqhFXXu77ErDd/xkREpGuk4MyYkk4a+XDWAMqe0S3KkelYQEQ==
+
+vscode-languageclient@^8.0.2:
+  version "8.0.2"
+  resolved "https://registry.yarnpkg.com/vscode-languageclient/-/vscode-languageclient-8.0.2.tgz#f1f23ce8c8484aa11e4b7dfb24437d3e59bb61c6"
+  integrity sha512-lHlthJtphG9gibGb/y72CKqQUxwPsMXijJVpHEC2bvbFqxmkj9LwQ3aGU9dwjBLqsX1S4KjShYppLvg1UJDF/Q==
+  dependencies:
+    minimatch "^3.0.4"
+    semver "^7.3.5"
+    vscode-languageserver-protocol "3.17.2"
+
+vscode-languageserver-protocol@3.17.2:
+  version "3.17.2"
+  resolved "https://registry.yarnpkg.com/vscode-languageserver-protocol/-/vscode-languageserver-protocol-3.17.2.tgz#beaa46aea06ed061576586c5e11368a9afc1d378"
+  integrity sha512-8kYisQ3z/SQ2kyjlNeQxbkkTNmVFoQCqkmGrzLH6A9ecPlgTbp3wDTnUNqaUxYr4vlAcloxx8zwy7G5WdguYNg==
+  dependencies:
+    vscode-jsonrpc "8.0.2"
+    vscode-languageserver-types "3.17.2"
+
+vscode-languageserver-types@3.17.2:
+  version "3.17.2"
+  resolved "https://registry.yarnpkg.com/vscode-languageserver-types/-/vscode-languageserver-types-3.17.2.tgz#b2c2e7de405ad3d73a883e91989b850170ffc4f2"
+  integrity sha512-zHhCWatviizPIq9B7Vh9uvrH6x3sK8itC84HkamnBWoDFJtzBf7SWlpLCZUit72b3os45h6RWQNC9xHRDF8dRA==
+
 watchpack@^2.4.0:
   version "2.4.0"
   resolved "https://registry.yarnpkg.com/watchpack/-/watchpack-2.4.0.tgz#fa33032374962c78113f93c7f2fb4c54c9862a5d"