SvelteKit Contributing Guide

April 4, 2026 ยท View on GitHub

Preparing

This is a monorepo, meaning the repo holds multiple packages. It requires the use of pnpm. You can install pnpm with:

npm i -g pnpm

pnpm commands run in the project's root directory will run on all sub-projects. You can checkout the code and install the dependencies with:

git clone git@github.com:sveltejs/kit.git
cd kit
pnpm install

Testing Changes

Playground

You can use the playground at playgrounds/basic to experiment with your changes to SvelteKit locally.

Linking local changes

If you want to test against an existing project, you can use pnpm overrides in that project:

{
	// ...
	"pnpm": {
		"overrides": {
			"@sveltejs/kit": "link:../path/to/svelte-kit/packages/kit",
			// additionally/optional the adapter you're using
			"@sveltejs/adapter-auto": "link:../path/to/svelte-kit/packages/adapter-auto"
		}
	}
}

Testing PR changes

Each pull request will be built and published via pkg.pr.new/. You can test the change by installing the package with your PR number:

npm add https://pkg.pr.new/sveltejs/kit/@sveltejs/kit@YOUR_PR_NUMBER_GOES_HERE

Code structure

Entry points to be aware of are:

Good first issues

If you're looking for an issue to tackle to get familiar with the codebase and test suite, the low hanging fruit label contains issues that ought to be relatively straightforward to fix. Check to see if a PR already exists for an issue before working on it!

Issues that have a clear solution but which may be slightly more involved have the ready to implement label.

Issues with the soon milestone are higher priority than issues with the later label (though PRs for 'later' issues are still welcome, especially if you're affected by them).

Testing

Run pnpm test:kit to run the tests from the packages/kit directory. You can also run pnpm test:others to run tests from all packages except the packages/kit directory. Browser tests live in subdirectories of packages/kit/test such as packages/kit/test/apps/basics.

You can run the tests for only a single package by first moving to that directory. E.g. cd packages/kit.

For some packages you must rebuild each time before running the tests if you've made code changes. These packages have a build command. Packages like packages/kit don't require a build step.

To run a single integration test or otherwise control the running of the tests locally see the Playwright CLI docs. Note that you will need to run these commands from the test project directory such as packages/kit/test/apps/basics.

You can run the test server with cd packages/kit/test/apps/basics; pnpm run dev to hit it with your browser. The Playwright Inspector offers similar functionality.

You may need to install some dependencies first, e.g. with npx playwright install-deps (which only works on Ubuntu).

If there are tests that fail on the CI, you can retrieve the failed screenshots by going to the summary page of the CI run. You can usually find this by clicking on "Details" of the check results, clicking "Summary" at the top-left corner, and then scrolling to the bottom "Artifacts" section to download the archive.

It is very easy to introduce flakiness in a browser test. If you try to fix the flakiness in a test, you can run it until failure to gain some confidence you've fixed the test with a command like:

pnpx playwright test --workers=1 --repeat-each 1000 --max-failures 1 -g "accepts a Request object"

The Playwright tests can also be run with the following environment variables to augment how the tests run locally:

# Default values
KIT_E2E_BROWSER=chromium
KIT_E2E_RETRIES=0
KIT_E2E_WORKERS=undefined

# Append the modified environment variable before the test command
KIT_E2E_RETRIES=2 pnpm test:kit

Working on Vite and other dependencies

If you would like to test local changes to Vite or another dependency, you can build it and then use pnpm.overrides. Please note that pnpm.overrides must be specified in the root package.json and you must first list the package as a dependency in the root package.json:

{
	// ...
	"dependencies": {
		"vite": "^4.0.0"
	},
	"pnpm": {
		"overrides": {
			"vite": "link:../path/to/vite/packages/vite"
		}
	}
}

Documentation changes

All documentation for SvelteKit is in the documentation directory, and any improvements should be made as a Pull Request to this repository. The site itself is located in the sveltejs/svelte.dev repo and can be run locally to preview changes.

Sending PRs

When you open a PR, the PR template includes a checklist. Please read it carefully and don't delete it.

Run tests locally before submitting. CI runs the full suite, but catching failures early saves time for everyone. At a minimum, run pnpm format, pnpm lint, pnpm check, and pnpm -F @sveltejs/kit test:unit.

Coding style

There are a few guidelines we follow:

  • Internal variables are written with snake_case while external APIs are written with camelCase
  • Provide a single object as the argument to public APIs. This object can have multiple properties
  • Avoid creating new test projects under packages/kit/test/apps but reuse an existing one when possible
  • Ensure pnpm lint and pnpm check pass. You can run pnpm format to format the code

To use the git hooks in the repo, which will save you from waiting for CI to tell you that you forgot to lint, run this:

git config core.hookspath .githooks

Generating changelogs

For changes to be reflected in package changelogs, run pnpm changeset and follow the prompts.

Type changes

If your PR changes the generated types of SvelteKit, run pnpm generate:types inside packages/kit and commit the new output (don't format it with Prettier!). Review the changes carefully to ensure there are no unwanted changes. If you don't commit type changes, CI will fail.

Releases

The Changesets GitHub action will create and update a PR that applies changesets and publishes new versions of changed packages to npm.

New packages will need to be published manually the first time if they are scoped to the @sveltejs organisation, by running this from the package directory:

npm publish --access=public