Installation

Pyro is one npm package, @povio/lightning-panda. It contains the browser binaries, the lightningpanda CLI and the TypeScript client. Installing it runs no install scripts and downloads nothing else.

Names in code

Pyro is the product name. The package, command and APIs keep their current names: the npm package @povio/lightning-panda, the lightningpanda command, the Lightningpanda class, the Lightningpanda.* CDP domain and the LIGHTNINGPANDA_* environment variables. Use those names in code and scripts.

Install the package

Add it as a development dependency:

bun

bun add --dev @povio/lightning-panda

npm

npm install --save-dev @povio/lightning-panda

Release candidates are published under the next dist-tag:

bun

bun add --dev @povio/lightning-panda@next

npm

npm install --save-dev @povio/lightning-panda@next

Stable releases go to latest. Publishing a stable version does not move next, so next can point at an older release candidate after a stable release. Check Changelog and versions before you pin.

Requirements

What	Requirement
Browser on macOS	macOS 14 or newer, Apple silicon or Intel
Browser on Linux	x64 or arm64 with glibc 2.39 or newer (Ubuntu 24.04, Debian 13, Fedora 40 or newer)
Client API	Node.js 22+ or Bun. Bun loads the TypeScript sources; Node loads the compiled JavaScript and type declarations.
lightningpanda test (Playwright runner)	Bun on PATH: tests run in bun test worker processes
lightningpanda e2e (suite runner)	Bun on PATH: the runner runs on Bun, and expect is Bun's

Other operating systems, including Windows, can use the client against a browser running elsewhere. See Remote browsers.

What is bundled

The package carries one browser per platform under native/:

Directory	Platform	JavaScriptCore	Fork mode
native/darwin-arm64/	macOS, Apple silicon	patched build, bundled	yes
native/darwin-x64/	macOS, Intel	macOS system framework	no
native/linux-x64/	Linux x64	patched build, bundled, with its ICU libraries in lib/	yes
native/linux-arm64/	Linux arm64	patched build, bundled, with its ICU libraries in lib/	yes

Every bundled browser is built with rendering enabled: layout, screenshots and PDF work out of the box. Fork mode (serve --fork) needs the patched JavaScriptCore, which is why the Intel macOS build does not have it. See Fork mode.

The package has no os restriction in package.json, so it installs everywhere. On an unsupported platform, launching a local browser fails with a clear error; connecting to a remote one still works.

Verify the install

Run version through your package manager:

bun

bunx lightningpanda version

npm

npx lightningpanda version

The output names the version and what the engine can do:

lightningpanda 0.0.33
engine: JavaScriptCore; capabilities: Capabilities { weak_refs: true, modules: true, import_maps: true, typed_modules: true, unhandled_rejections: true, termination: true, hidden_properties: true, proxy_targets: true, object_global_context: true, fork: true, global_constants: true }

fork: true means this binary supports fork mode. On Intel Macs it reads fork: false.

A second check runs a script in a blank page:

bunx lightningpanda eval -e 'console.log(navigator.userAgent)'
# Mozilla/5.0 (compatible; lightningpanda/0.0.33)

How the binary is chosen

Lightningpanda.launch(), the Playwright module and the CLI pick the browser in this order:

1. the bin option (Lightningpanda.launch({ bin }), or use: { lightningpanda: { bin } } in a Playwright config);
2. the LIGHTNINGPANDA_BIN environment variable;
3. a lightningpanda binary next to the package, when the package was unpacked from a GitHub release archive;
4. the bundled binary for the current platform and architecture.

The CLI and launch() never fall back to another lightningpanda on your PATH. Set LIGHTNINGPANDA_BIN to use a browser you built from source or downloaded separately:

LIGHTNINGPANDA_BIN=/opt/lightningpanda/lightningpanda bunx lightningpanda test

Copying binaries on macOS

The macOS binaries are signed ad hoc with the com.apple.security.cs.allow-jit entitlement. Without it, JavaScriptCore runs every script in its interpreter, which is much slower. Copying the file keeps the signature; re-signing it, or stripping it, removes the entitlement. Copy the whole native/<platform>/ directory, including lib/ when present. See Platforms for how to re-sign.

Remote browsers

You can run the browser on one machine and the client on another. This is how Windows machines, and containers without a supported glibc, use Pyro.

On the browser host, listen on an address the client can reach:

lightningpanda serve --host 0.0.0.0 --port 9222 --advertise-host browser.internal

--advertise-host is the host name written into /json/version, so clients that discover the WebSocket URL over HTTP get one they can reach. The server has no authentication: expose it only on a trusted network.

On the client, connect instead of launching:

import { Lightningpanda } from '@povio/lightning-panda';

const lp = await Lightningpanda.connect('ws://browser.internal:9222/');

For Playwright-style tests, set LIGHTNINGPANDA_WS=ws://browser.internal:9222/ or use: { lightningpanda: { wsEndpoint } }. Installing or importing the client never starts a local browser by itself.

Paths given to the server, such as --static directories or file uploads given as paths, refer to the browser host's file system.

CI

The package's own release workflow tests the packed tarball on GitHub-hosted macos-15, macos-15-intel, ubuntu-24.04 and ubuntu-24.04-arm runners, with Node 22 and Bun. Those images work without extra setup. On GitHub Actions:

jobs:
  e2e:
    runs-on: ubuntu-24.04
    steps:
      - uses: actions/checkout@v4
      - uses: oven-sh/setup-bun@v2
      - run: bun install --frozen-lockfile
      - run: bunx lightningpanda version
      - run: bunx lightningpanda e2e e2e --concurrency 8 --junit junit.xml

For containers, use a base image with glibc 2.39 or newer, such as ubuntu:24.04 or debian:trixie. The Linux browser links libfontconfig.so.1 and libstdc++.so.6. Slim images may lack fontconfig and fonts; install them if text is missing from screenshots and PDFs:

FROM ubuntu:24.04
RUN apt-get update \
 && apt-get install -y --no-install-recommends ca-certificates libfontconfig1 fonts-dejavu-core \
 && rm -rf /var/lib/apt/lists/*

Linux browsers are built and tested in CI only; the project publishes no Linux performance measurements yet. CI recipes has complete pipelines, including sharding.

Building from source

The browser builds with Cargo from the repository on macOS. Source builds are not needed to use the package; they matter if you want profile-guided optimization or a patched engine. The repository README covers the build, the JIT signing contract and the optional PGO flow.