Nix Chrome DevTools

One-click setup for the Chrome DevTools MCP server in any Nix-based project. Delivered as an APM package: add a single line to your project's apm.yml and apm install does the rest — Chrome (Playwright's bundled Chrome-for-Testing) and Node.js resolve through Nix; the MCP server gets wired into every supported harness's runtime config (Claude Code, Codex, OpenCode, …). No devshell to author, no flake to compose. The nixpkgs source is overridable per process or system-wide.

See introductory blog post.

Usage

Add to your project's apm.yml:

dependencies:
  apm:
    - juspay/nix-chrome-devtools-mcp

apm install aggregates the MCP entry from this package's apm.yml into your runtime configs (.mcp.json, .codex/config.toml, opencode.json).

Requirements

Nix — see nixos.asia/en/install. Flakes must be enabled (experimental-features = nix-command flakes).

Overrides

The launcher reads two env vars:

Var	Default	Effect
NIXPKGS_FLAKE	nixpkgs	flake-ref used to resolve playwright-driver.browsers and nodejs. Examples: github:NixOS/nixpkgs/<rev>, path:/abs/path/to/local/nixpkgs.
CHROME_DEVTOOLS_MCP_VERSION	latest	npm dist-tag or version of chrome-devtools-mcp to install via npx -y. Pin to a specific version (e.g. 0.26.0) when you need reproducibility.

System-wide overrides also work:

• nix registry pin nixpkgs github:NixOS/nixpkgs/<rev> (replaces the default nixpkgs registry alias).
• Declare an overriding mcp: entry for chrome-devtools in the consumer's root apm.yml (root deps win APM's name-first dedupe).

Screencast (video) recording

The launcher runs the server with --experimentalScreencast=true and puts ffmpeg on its PATH (resolved through Nix, same as Chrome and Node), so the screencast_start / screencast_stop tools are available out of the box. They record the selected page to an .mp4/.webm file via Puppeteer's page.screencast(), which shells out to ffmpeg — no host ffmpeg install needed.

Chrome version compatibility

chrome-devtools-mcp is always pulled at @latest via npx. Each release transitively pins a Puppeteer version that expects a specific Chrome-for-Testing milestone; nixpkgs' playwright-driver.browsers provides a Chrome that may run a few major versions behind. CDP is largely backward-compatible, so the core operations (navigate, evaluate, take_snapshot, network/console inspection, screenshots) work, but Lighthouse-driven tooling (performance_* insights) is the most version-sensitive piece. If a chrome-devtools-mcp release breaks against your nixpkgs Chrome, override NIXPKGS_FLAKE to a newer nixpkgs revision whose Playwright Chrome matches Puppeteer's expected milestone.

License

Apache 2.0 — see LICENSE.