VS Code Extension not loading in Extension Development Host

Question

I generated a sample extension by following. https://code.visualstudio.com/api/get-started/your-first-extension

When i run the extension from the debug view and search for the extension "Hello World". It does not appears in the command palette at all.

my package.json

{
  "name": "testextension",
  "displayName": "TestExtension",
  "description": "",
  "version": "0.0.1",
  "engines": {
    "vscode": "^1.76.0"
  },
  "categories": [
    "Other"
  ],
  "activationEvents": [],
  "main": "./out/extension.js",
  "contributes": {
    "commands": [
      {
        "command": "testextension.helloWorld",
        "title": "Hello World"
      }
    ]
  },
  "scripts": {
    "vscode:prepublish": "npm run compile",
    "compile": "tsc -p ./",
    "watch": "tsc -watch -p ./",
    "pretest": "npm run compile && npm run lint",
    "lint": "eslint src --ext ts",
    "test": "node ./out/test/runTest.js"
  },
  "devDependencies": {
    "@types/vscode": "^1.76.0",
    "@types/glob": "^8.1.0",
    "@types/mocha": "^10.0.1",
    "@types/node": "16.x",
    "@typescript-eslint/eslint-plugin": "^5.53.0",
    "@typescript-eslint/parser": "^5.53.0",
    "eslint": "^8.34.0",
    "glob": "^8.1.0",
    "mocha": "^10.2.0",
    "typescript": "^4.9.5",
    "@vscode/test-electron": "^2.2.3"
  }
}

extension.ts

// 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';

// 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) {

    // Use the console to output diagnostic information (console.log) and errors (console.error)
    // This line of code will only be executed once when your extension is activated
    console.log('Congratulations, your extension "testextension" is now active!');

    // 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
    let disposable = vscode.commands.registerCommand('testextension.helloWorld', () => {
        // The code you place here will be executed every time your command is executed
        // Display a message box to the user
        vscode.window.showInformationMessage('Hello World from TestExtension!');
    });

    context.subscriptions.push(disposable);
}

// This method is called when your extension is deactivated
export function deactivate() {}

Answer 1

In an extension, the engines.vscode property specifies the minimum version of VS Code itself required to run the extension.

package.json

"engines": {
    "vscode": "^1.76.0"
}

There is no message in the developer setup telling you that your own version is outdated; the extension just won't load.

So always use the latest version of VC Code to develop extensions, or try to change the required version in the package.json.