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Cypress Monorepo — AGENTS.md

Overview

Cypress is an open-source end-to-end and component testing framework for the modern web. This monorepo ships the Cypress desktop application and CLI (cypress), the JavaScript driver that runs tests in the browser, the Electron-based test runner, a suite of published npm packages (component testing adapters, webpack/vite dev-server integrations, plugins), and the internal tooling used to build and release all of it. Cypress is used by millions of developers to test web applications across Chrome, Firefox, Edge, WebKit, and Electron.

Workspaces

  • cli/ — The main cypress npm package (CLI entry point) and co-located component testing framework adapters (@cypress/react, @cypress/vue, @cypress/angular, @cypress/svelte, @cypress/mount-utils)
  • packages/ — Core internal packages: the test driver, Electron app, HTTP server, proxy, rewriter, launcher, frontend Vue app, launchpad, reporter, config, data-context, telemetry, types, errors, and more (33 packages total)
  • npm/ — Publicly published npm packages: bundler integrations, component testing adapters, plugins, and dev tooling (15 packages)
  • tooling/ — Internal build tooling: V8 snapshot creation, packherd dependency bundler, and electron-mksnapshot (3 packages)
  • system-tests/ — Full end-to-end system test suite run against a built Cypress binary
  • scripts/ — Internal build, release, and CI automation scripts

Prerequisites

  • Node: Use the node version specified in the .node-version file (check with node -v; run nvm use to manage versions)
  • Package manager: Yarn 1 (yarn@1.22.22) — do not use npm or pnpm
  • Lerna: Orchestrated via root package.json scripts; installed as a dev dependency
  • Electron (for binary builds): handled automatically by @packages/electron during build

Common Commands

Setup & Development

# Install all dependencies (runs post-install hooks automatically)
yarn

# Start Cypress in dev mode (watch, rebuilds on change)
yarn dev

# Open the Cypress GUI in dev + global mode
yarn start

Testing

# Run tests scoped to a single package (preferred over bare yarn test)
yarn test --scope @packages/server

# Target a specific vitest spec file (packages that use vitest)
yarn workspace @packages/config test -- <path-to-spec>

# Target a specific vitest spec by glob pattern
yarn workspace @packages/net-stubbing test -- "<glob-pattern>"

# Target a specific mocha spec file (packages that use mocha)
yarn workspace @packages/server test-unit -- <path-to-spec>

# Filter mocha tests by name pattern
yarn workspace @packages/server test-unit -- --grep "<pattern>"

# Run system tests (full binary-level E2E)
yarn test-system

# Run Cypress headlessly against a specific spec (dev mode)
yarn cypress:run -- --spec "path/to/spec.cy.ts"

# Run Cypress component tests against a specific spec (dev mode)
yarn cypress:run:ct -- --spec "path/to/spec.cy.ts"

Type Checking

# Type-check all TypeScript across the monorepo
yarn type-check

# Lerna-only type check pass
yarn check-ts

Linting & Formatting

# Lint all packages (no bail, concurrency 2)
yarn lint

# Lint and auto-fix specific scopes
yarn lint:fix

Note: This project does not use Prettier. All formatting is enforced via ESLint.

Build

# Full monorepo build
yarn build

# Build V8 snapshot (dev)
yarn build-v8-snapshot-dev

# Build V8 snapshot (prod)
yarn build-v8-snapshot-prod

# Clean all build artifacts
yarn clean

# Clean and reinstall (nuclear)
yarn clean-deps && yarn

Architecture

CLI & Distribution

  • cypress (cli/) — The cypress npm package users install. Entry point for cypress open, cypress run, cypress install, etc. Version: 15.x.

Test Runner & Driver

  • @packages/driver — The JavaScript test driver that executes user test code inside the browser. Implements Cypress commands, assertions, retries, and all cy.* APIs.
  • @packages/runner — The webpack-bundled runner UI that hosts the AUT (application under test) iframe and driver communication layer.
  • @packages/app — The Vue 3 frontend for the Cypress GUI / Launchpad. Main visual interface for the desktop app.
  • @packages/launchpad — Project creation, onboarding, and test file scaffold UI.
  • @packages/frontend-shared — Shared Vue components and design system tokens used by app and launchpad.
  • @packages/reporter — The test results reporter UI component (pass/fail tree, log panel).

Server & Network

  • @packages/server — HTTP server responsible for serving test files, handling browser launching, socket communication, and orchestrating the test run.
  • @packages/proxy — HTTP/S proxy that intercepts all browser traffic during a test run.
  • @packages/net-stubbing — Network stubbing (cy.intercept) implementation — request matching, response manipulation.
  • @packages/network — Low-level network protocol utilities.
  • @packages/network-tools — Higher-level networking helpers used across packages.
  • @packages/https-proxy — HTTPS proxy implementation for TLS interception.
  • @packages/rewriter — JavaScript source rewriter that transforms test and app code for Cypress compatibility (instrument, polyfill, inject).

Configuration & Data

  • @packages/config — Configuration types, defaults, validation, and the public defineConfig API.
  • @packages/data-context — Centralized GraphQL data access layer for the Cypress app (projects, specs, runs, settings).
  • @packages/scaffold-config — Logic for scaffolding new testing setups via Launchpad (framework detection, config file generation).

Desktop & Electron

  • @packages/electron — Electron runtime wrapper, binary building utilities, and auto-update integration.
  • @packages/launcher — Browser detection and launch logic for Chrome, Firefox, Edge, WebKit, and Electron.
  • @packages/extension — WebExtension injected into browsers to enable cross-origin features and automation hooks.

Types, Errors & Utilities

  • @packages/types — Shared TypeScript type definitions used across all packages.
  • @packages/errors — Cypress error definitions, error templates, and error utilities.
  • @packages/socket — WebSocket communication library used for driver ↔ server messaging (browser and Node sides).
  • @packages/telemetry — OpenTelemetry instrumentation wrapper used throughout the monorepo.
  • @packages/icons — Icon registry and SVG assets.
  • @packages/stderr-filtering — Stderr output filtering utilities.

Build & Snapshot Infrastructure

  • @packages/v8-snapshot-require — Module loading utilities for V8 snapshots in Electron.
  • @packages/packherd-require — Module loader for dependencies bundled by @tooling/packherd.
  • @packages/web-config — Webpack/PostCSS configuration for the Vue frontend bundles.
  • @packages/ts — Shared TypeScript configuration and ts-node register helper.
  • @packages/eslint-config — Shared ESLint configuration preset used across packages.
  • @packages/resolve-dist — Resolves paths to compiled distribution artifacts.
  • @tooling/v8-snapshot — V8 snapshot creation tooling for Electron startup optimization.
  • @tooling/packherd — Bundles all reachable dependencies from an entry point into a single artifact.
  • @tooling/electron-mksnapshot — Configurable mksnapshot binary wrapper for the target Electron version.

Component Testing Adapters (published via npm/)

  • @cypress/react — Component testing adapter for React.
  • @cypress/vue — Component testing adapter for Vue.js.
  • @cypress/angular — Component testing adapter for Angular.
  • @cypress/angular-zoneless — Angular adapter without zone.js.
  • @cypress/svelte — Component testing adapter for Svelte.
  • @cypress/mount-utils — Shared utilities used by all component testing adapters.

Bundler Integrations (published via npm/)

  • @cypress/webpack-dev-server — Webpack Dev Server launcher for component testing.
  • @cypress/vite-dev-server — Vite Dev Server launcher for component testing.
  • @cypress/webpack-preprocessor — Webpack preprocessor for bundling test spec files.
  • @cypress/webpack-batteries-included-preprocessor — Webpack preprocessor with batteries included (TypeScript, CoffeeScript, etc.).
  • @cypress/vite-plugin-cypress-esm — Vite plugin for mutable ESM modules in browser tests.

Plugins & Dev Tooling (published via npm/)

  • @cypress/grep — Plugin to filter test runs by substring/tag.
  • @cypress/puppeteer — Plugin to enhance Cypress tests with Puppeteer.
  • @cypress/schematic — Official Angular CLI schematic for adding Cypress.
  • @cypress/eslint-plugin-dev — ESLint rules shared across Cypress development packages.

Code Conventions

  • No Prettier — Formatting is enforced entirely through ESLint. The .prettierignore excludes all files.
  • Single quotes — 'single' quote style required for all JS/TS.
  • No semicolons — Enforced via ESLint (semi: 'never').
  • 2-space indentation — Standard across all JS/TS files.
  • Trailing commas — Required in multiline contexts (comma-dangle: 'always-multiline').
  • No var — var declarations are an ESLint error; use const or let.
  • Template literals — prefer-template: 'error' — no string concatenation.
  • Object shorthand — object-shorthand: 'error'.
  • No console — no-console: 'error'; use the logger utilities instead.
  • TypeScript: strict: true base, but noImplicitAny: false (implicit any allowed for pragmatic reasons).
  • Type-only imports: importsNotUsedAsValues: "error" — use import type for type-only imports.
  • Unused vars: Prefix with _ to suppress (argsIgnorePattern: '^_').
  • No .only in tests — mocha/no-exclusive-tests: 'error' (ESLint). Caught by yarn lint and by pre-commit ESLint (lint-staged). For intentional .only in fixtures or type samples, use eslint-disable-next-line mocha/no-exclusive-tests (with a short comment).
  • .skip requires a comment — Must include NOTE:, TODO:, or FIXME: comment explaining why.
  • Blank line before return — Enforced via padding-line-between-statements.
  • Sync FS calls — Flagged with a warning (except existsSync); prefer async variants.

Code Comments

  • Prefer none — Always prefer no code comment if the code is self-explanatory.
  • Explain the why — When a comment is necessary, use it to explain the why and anything relevant that is not directly expressed by the code itself.
  • Don't repeat yourself — Do not restate the same comment multiple times in a file as the code flows through each step.
  • Present state only — Keep comments relevant to the current state of the code. Do not describe what changed or how the code used to be different.

Bad examples:

// never wipe the entire jar - the old hack called clearCookies() with no filter
// we no longer need to clear the state here, CDP added automatically clearing
// Firefox previously relied on os-level focus, now we use WebDrive BiDi to focus

Good examples:

// Close any extra pages so they don't leak into other tests
// Firefox doesn't support this in native BiDi, so we pull remote.location from current frame
// `cookie`'s serializer rejects an IPv6 literal Domain (e.g. `[::1]`), crashing
// the proxy. Browsers scope cookies for IP hosts to that host anyway, so omit
// Domain and let the cookie default to host-only.

Pull Requests

CONTRIBUTING.md is the source of truth for PR conventions, including the semantic-release title prefix that determines the next version. The other essentials:

Changelog & Template

CI/CD

  • Primary CI: CircleCI. Config lives in .circleci/src/ (modular) and is compiled to .circleci/packed/pipeline.yml. See .circleci/AGENTS.md for when to add a branch to the full-CI allowlist (binary tests, Windows jobs, v8 snapshot validation).
  • Supplementary: GitHub Actions for security scanning (Snyk), SBOM generation, browser version auto-updates, and PR validation.
  • Base branch: develop — all PRs target develop; release branches follow release/X.Y.Z.
  • Multi-platform matrix: Linux x64, Linux ARM64, macOS x64, macOS ARM64, Windows — all run in parallel.
  • Release gate: All tests must pass through the ready-to-release aggregation job before npm-release runs.
  • External PRs: Require manual approval via approve-contributor-pr gate before CI runs.
  • Binary builds: Triggered separately after npm release; cross-platform binaries are assembled and distributed via CDN.

Cursor Cloud specific instructions

Environment

  • Node.js >= 22.19.0 and Yarn 1.22.22 are pre-installed. The update script runs yarn which triggers the full postinstall (patch-package, yarn-deduplicate, rebuild better-sqlite3, lerna build, V8 snapshot).
  • Xvfb is already running on DISPLAY=:1. Chrome is available at /usr/bin/google-chrome-stable.

Running Cypress in dev mode

  • yarn dev starts the Cypress Electron GUI in global/dev mode (Launchpad). It builds Vite bundles for @packages/app and @packages/launchpad, then launches Electron. The GraphQL server runs at http://localhost:4444/__launchpad/graphql.
  • yarn cypress:run -- --project <path> --browser chrome --headless runs Cypress headlessly in dev mode. The config file at the target project must NOT require('cypress') since it resolves from the project root.

Running tests

  • Prefer scoped tests: yarn workspace @packages/<name> test (vitest) or yarn test --scope @packages/<name> (lerna).
  • Some test suites (e.g., @packages/network) require privileged ports (443) and will fail with EACCES in unprivileged containers — this is expected.
  • @packages/config has 2 tests that assert cypressBinaryRoot contains 'cypress'; these fail when the workspace directory name differs (e.g., /workspace). This is a known path-dependent issue, not a code bug.

Linting

  • yarn lint --scope @packages/<name> for focused lint. Full monorepo lint: yarn lint.

Key caveats

  • The postinstall takes ~4-5 minutes (build + V8 snapshot generation). If yarn is interrupted, re-run it.
  • yarn --frozen-lockfile should be preferred when the lockfile hasn't changed; it falls back to yarn (which runs postinstall) if it fails.
  • Do not run yarn from within sub-packages. Always run from the repo root.