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John Papa for Microsoft Azure

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Is Your VS Code Extension Slow? Here's How to Speed it Up!

- Extensions Rock -

VS Code users (and there are a lot of us) just love our extensions. There are thousands of VS Code extension to choose from and many of us have several installed. They do everything from lighting up your favorite language, formatting your code, or even colorizing your theme.

Have you ever noticed that some extensions take a few moments to initialize as you start VS Code? What might cause this delay?

What can you do about it? A lot actually. Stay with me to see how you can help your favorite extensions load fast!

One possible cause is the number of files or the size of the extension. Some extensions have so much functionality in them that they can slow down over time.

Wait, Why is that?

When we build apps for the web, we write dozens or hundreds of files in JavaScript, CSS, and HTML. We don't want to send 1,000 files across the web to a browser as it may be a poor experience of waiting and waiting. When we write our code it isn't optimized for the browser quite as much as it can be, either. Modern tools help us solve this by compressing the files into a single (or a small set) of files. One popular tool is WebPack.

If you use the command to "Developer: Show Running Extensions" you will see a list of the activated extensions in your VS Code instance. You will also see, to the right, how long each extension took to activate in ms.

Show Running Extensions

This is a great way to find out which ones may be slower activating. Notice the list below from my instance of VS Code shows a few of my installed extensions and their activation times. Obviously, some take longer than others to load, because they do more.

Running Extensions

What can you do if one is taking too long for your tastes? (maybe 1000ms?)

Making Extensions Faster

Recently the VS Code team released the ability to use WebPack to bundle the files in extensions.

The article covers it all really, and it can help when packaging an extension.

I found that my Peacock extension was putting 48 files in the package. I made a few tweaks and I cut this down by a lot.

First, I added some file to the .vscodeignore file

# Files I excluded

# After webpack, we have more to ignore

Then I created a new branch for my extension. I went through the steps in the VS Code docs to update my project to use WebPack.

My goals were to make all of these still work:

  • packaging with npm run package
  • publishing with npm run publish
  • local and CI testing with npm run test
  • F5 debugging with the launch.json
  • F5 debugging the tests with the launch.json

The approach has me compiling both with webpack and tsc for the tests and debugging.

Here is my project

Changed my main file in package.json

  "main": "./dist/extension",

My npm scripts in package.json

  "scripts": {
    "package": "npx vsce package",
    "publish": "npx vsce publish",

    "vscode:prepublish": "webpack --mode production",
    "compile": "webpack --mode none",
    "watch": "webpack --mode none --watch",

    "postinstall": "node node_modules/vscode/bin/install",
    "just-test": "node node_modules/vscode/bin/test",
    "test-compile": "tsc -p ./ && npm run compile",
    "test": "npm run test-compile && node node_modules/vscode/bin/test"

My launch.json configurations for debugging the runtime and tests:

  "configurations": [
      "name": "Run Extension",
      "type": "extensionHost",
      "request": "launch",
      "runtimeExecutable": "${execPath}",
      "args": ["--extensionDevelopmentPath=${workspaceFolder}"],
      "outFiles": ["${workspaceFolder}/dist/**/*.js"],
      "preLaunchTask": "npm: test-compile"
      "name": "Extension Tests",
      "type": "extensionHost",
      "request": "launch",
      "runtimeExecutable": "${execPath}",
      "args": [
      "outFiles": ["${workspaceFolder}/out/test/**/*.js"],
      "preLaunchTask": "npm: test-compile"

And here is the entire repo where you can see everything in context 👇

GitHub logo johnpapa / vscode-peacock

Subtly change the color of your Visual Studio Code workspace. Ideal when you have multiple VS Code instances, use VS Live Share, or use VS Code's Remote features, and you want to quickly identify your editor.

Peacock for Visual Studio Code

Peacock Icon

Subtly change the color of your Visual Studio Code workspace. Ideal when you have multiple VS Code instances, use VS Live Share, or use VS Code's Remote features, and you want to quickly identify your editor.

Read the extensive documentation here which includes a guide on how to use Peacock and a changelog

Badge for version for Visual Studio Code extension johnpapa.vscode-peacock Installs Downloads Rating Live Share

The MIT License All Contributors

Build Status Greenkeeper badge


  1. Open Extensions sideBar panel in Visual Studio Code and choose the menu options for View → Extensions
  2. Search for Peacock
  3. Click Install
  4. Click Reload, if required


Read the extensive documentation here which includes a guide on how to use Peacock and a changelog

Quick Usage

Let's see Peacock in action!

  1. Create/Open a VSCode Workspace (Peacock only works in a Workspace)
  2. Press F1 to open the command palette
  3. Type Peacock
  4. Choose Peacock: Change to a favorite color
  5. Choose one of the pre-defined colors and see how it changes…

What Kind of Impact Can it Have?

This is a great question, and one we should definitely ask. I mean, after all, to make any code change there has to be some value. I was able to get permission (thanks to the VS Code team and Erich Gamma) to share some performance stats (unofficial tests) of two extensions you may have used.

Both of these extensions have a considerable amount of logic in them and do some pretty impressive and useful things.

Azure Account

The Azure Account extension's size and number of files decreased considerably ... like from "holy moly" to "not bad"!

The warm activation is a term for how long it takes the extension to activate, when that extension has already been installed previously (not the first time). This was cut in half for this extension. Not bad at all!

  • Download size (the .vsix): 6.2M to 840K.

  • Packaged files: 4300 to 11

  • Warm activation time: 676ms to 338ms


The Docker extension had a noticeable warm activation improvements to under 2 seconds. But the key aspect is the cold activation time. Cold activation is how long it might take the extension to activate when it was just installed.

  • Warm activation time: 3.5s to <2s

  • Cold activation time (after 1st install): 20s to 2s


Several things are affected by using webpack to bundle an extension. This is why it's super important to test all of these out.

  • Run the extension locally in your debugger (and test you can hit a breakpoint)
  • Package the extension and load it (load from VSIX) from the menu
  • Run your tests with your debugger (and test you can hit a breakpoint)
  • Run your test script from npm test

When you are done, you can check the activation time again.

But I Didn't Write the Extension

That's OK, that but if you like the extension, consider creating a pull request (PR) on its repository to enabled webpack bundling!

The great thing about OSS is that everyone gets a voice. This is a great way to help your favorite projects and your peers!

Thanks to Erich Gamma for pointing this out to me!

Cross posted to

Top comments (6)

coreyja profile image
Corey Alexander

What was your before and after loading times for the Peacock extension? Curious to see how big the savings here are!

I was under the impression that one reason we (collectively) try to bundle JS assets is to not have to deal with downloading multiple large files over HTTP,but the extension files should be already downloaded locally,so I wonder what the benefit of using Webpack here is 🤔

john_papa profile image
John Papa

Good questions!

Webpack reduces the size to just the code we use and makes some other optimizations. So in this case, that is helping. I've asked the VS Code team to clarify whether the number of files has an impact or not.

Ph - and Peacock was anywhere from 8ms to 16ms to activate before, and 6ms to 14ms after. (I tried it 5 times each, with totally unscientific measuring)

coreyja profile image
Corey Alexander

Ahh yes I was forgetting about tree shaking and the like!

I'm interested in if the number of files makes a significant difference as well! Thanks for the response!

Thread Thread
john_papa profile image
John Papa

I was told yes, the number of files will also affect load time.

BTW - I updated the post with some more stats that are pretty impressive. Thanks to the VS Code
team for sharing these and giving me permission to share with you all!

dillpickle80 profile image

Do you know if there is any resource available to evaluate the intersectionnal impact of different extensions when combined? Else, do you know of a conveniant and relatively quick way to verify on our own? There seems to be extensions working very fine alone, that once coupled with other extensions ends up stepping on each other's toes and making VSCode significantly slower.

nedcode profile image
Ned Marafawi

This actually did help a little bit but I still need to disable some of the extensions so my VS Code can run smooth. Thank you for the article!