Building a "Hello, world!" Sourcegraph extension

Sourcegraph extensions lets you add features and show new kinds of information alongside your code on, GitHub, and other code hosts.

This guide shows you how to create a simple Sourcegraph extension that:

  • Shows a friendly "Hello, world! 🎉🎉🎉" message when you hover over code.
  • Works on all code on GitHub (requires the Sourcegraph browser extension).
  • Works on all code on
  • Runs entirely client-side in the browser (your code remains local and is not sent to any server).


Follow the instructions for setting up your development environment so you can build and publish the extension.

Create the extension

Use the Sourcegraph extension creator to get started:

mkdir hello-world-extension
cd hello-world-extension
npm init sourcegraph-extension

Follow the prompts and once complete, view the code for the extension in the src directory. That's all it takes to create a simple extension!

Now let's publish it so you (and other people) can use it.

Publishing the extension

Publish the extension by running:

src ext publish

Now that the extension is published let's use it.

Use the extension

Open the URL found in the output from the publish command. This is the extension's listing page on the extension registry. Anyone can visit this page to see more information about the extension and to enable it.

Toggle the slider to enable the extension for your account. Now you can:

  • Visit any code file on Sourcegraph (such as this file) and hover over the code to see the "Hello, world! 🎉🎉🎉" message.
  • Visit any code file on GitHub (such as this file) and hover over the code to see it say the same.

Next steps

You've created your first Sourcegraph extension!

Now check out the Sourcegraph extensions authoring documentation to see how to build more powerful extensions.