Playwright Report MCP

An MCP (Model Context Protocol) server for running Playwright tests and reading structured results, failed test details, and attachment content — designed for AI agents doing test failure analysis.

---

Table of contents

• What it is
• What it is NOT
• Why
• Quick start
• Tools
• Attachments
• Installation
• Configuration
• Requirements
• Troubleshooting
• Development
• Cutting a release
• Contributing
• Release
• License

---

What it is

Playwright Report MCP gives an AI agent structured, token-efficient access to Playwright test outcomes. It runs your test suite, reads the JSON reporter output, and surfaces exactly what the agent needs: which tests failed, what the errors were, and the content of relevant attachments.

What it is NOT

There are many Playwright MCP servers that control a browser — they navigate pages, click elements, fill forms, and take screenshots. Playwright Report MCP is not one of those.

	Browser automation MCPs	Playwright Report MCP
Examples	microsoft/playwright-mcp, executeautomation/mcp-playwright	this project
Purpose	Let an AI agent drive a browser	Let an AI agent read test results
Runs tests	No	Yes
Returns pass/fail	No	Yes
Surfaces error messages	No	Yes
Reads attachment content	No	Yes

---

Why

The problem with existing approaches

Default reporters (list / dot) — Playwright's default reporters print human-readable output to stdout. Compact, but lossy: no attachment paths, no retry breakdown, no structured data.

HTML reporter (report.html) — A self-contained SPA bundle (typically 2–50 MB). Not machine-readable as text and exceeds any LLM context window.

Reading results.json directly — Works, but a full JSON report for even a small test suite is 10,000–20,000 tokens. For a failing test, most of that is passing test metadata you don't need.

What Playwright Report MCP does instead

• Filters results.json to only failed tests
• Returns structured, typed JSON the agent can act on immediately
• Exposes individual attachments by name so the agent fetches only what it needs
• Works on results produced by anyone — CI pipeline, a human, or the agent itself

Token cost comparison (one failed test in a 20-test suite)

Approximate input token counts based on Claude tokenization (~3–4 characters per token for mixed JSON/text content).

What you need	Without MCP — approach	Tokens (no MCP)	With MCP — tool calls	Tokens (MCP)	Savings
Error message only — live run	npx playwright test, read stdout (list/dot)	~500–1,200	run_tests + get_failed_tests	~300–500	~2×
Error message only — existing results	Read full results.json	~12,500–23,000	get_failed_tests	~300–500	~25–45×
+ page state at failure	+ read error-context file	~15,000–26,000	+ get_test_attachment('error-context')	~2,800–3,500	~4–7×
+ custom text attachments¹	+ read attachment files	~16,200–28,500	+ get_test_attachment ×2	~3,300–5,500	~4–5×
+ full page HTML snapshot²	+ read snapshot file	~41,000–103,000	+ get_test_attachment	~33,300–85,500	~1.2×

¹ Custom text attachments — e.g. AI diagnosis (~500–2,000 tokens) and console logs (~200–500 tokens) added via testInfo.attach() in your own fixtures.

² Full page HTML snapshot — a custom fixture that attaches the full rendered page HTML on failure. Large pages alone can reach 30,000–80,000 tokens and dominate cost regardless of whether MCP is used.

Key observations:

• For a live run, stdout (list/dot) is compact but gives the agent no path to attachment content — dead end for deeper analysis
• Reading results.json directly costs ~12,500–23,000 tokens even when only one test failed — most of it is passing test metadata the agent doesn't need
• The biggest MCP gains are in the middle rows: getting error messages + page state from existing results at ~4–45× lower token cost
• Full page HTML snapshot dominates cost either way; skipping it in favour of error-context is the single largest optimisation available

CI failure analysis

The primary use case: your CI pipeline runs the tests, the agent picks up the results after the fact and diagnoses failures. get_failed_tests reads results.json regardless of who triggered the run. No re-run needed.

---

Quick start

1. Install via npx (recommended)

No clone or build step needed — npx downloads and runs the server automatically:

{
  "mcpServers": {
    "playwright-report-mcp": {
      "command": "npx",
      "args": ["-y", "playwright-report-mcp"],
      "type": "stdio"
    }
  }
}

Or build from source:

git clone https://github.com/hubertgajewski/playwright-report-mcp.git
cd playwright-report-mcp
npm install && npm run build

2. Add the JSON reporter to your Playwright project

// playwright.config.ts
reporter: [
  ['json', { outputFile: 'test-results/results.json' }],
  ['html'], // keep any existing reporters
],

3. Register in .mcp.json

{
  "mcpServers": {
    "playwright-report-mcp": {
      "command": "npx",
      "args": ["-y", "playwright-report-mcp"],
      "type": "stdio"
    }
  }
}

4. Ask your AI agent

Run the Playwright tests and tell me what failed.

---

Compatibility

Tested with Claude Code (CLI). Should work with any MCP-compatible client that supports stdio transport, including Claude Desktop, Cursor, Cline, Windsurf, and Continue.dev — but these have not been verified.

---

Tools

All four tools accept an optional workingDirectory parameter — see Multi-worktree support.

run_tests

Runs the Playwright test suite and returns structured pass/fail results.

Input	Type	Description
workingDirectory	string (optional)	Playwright project directory. Absolute or relative to the MCP server launch directory. Defaults to ".". Must be under PW_ALLOWED_DIRS — see Multi-worktree support.
spec	string (optional)	Spec file path relative to the project directory, e.g. tests/login.spec.ts. Must stay within the project directory.
browser	enum (optional)	Chromium, Firefox, Webkit, Mobile Chrome, Mobile Safari
tag	string (optional)	Tag filter, e.g. @smoke
timeout	integer (optional)	Timeout in milliseconds for the whole test run. Defaults to 300000 (5 min). Use a larger value for long suites or a smaller one to fail fast. When the run is killed by this timeout, the tool returns an explicit error rather than a generic non-zero exit.

Returns: exit code, run stats, and a summary of all tests with status, duration, and error per project.

get_failed_tests

Returns failed tests from the last run with error messages and attachment paths. Does not re-run tests — reads the existing results.json.

Input	Type	Description
workingDirectory	string (optional)	See Multi-worktree support. Defaults to ".".

Returns: failed test count, titles, file paths, per-project status, error messages, and attachment paths.

get_test_attachment

Reads the content of a named text attachment for a specific test from the last run.

Input	Type	Description
workingDirectory	string (optional)	See Multi-worktree support. Defaults to ".".
testTitle	string	Exact test title as shown in the report
attachmentName	string	Attachment name, e.g. error-context, ai-diagnosis, page-html

Returns: the attachment content as text. Binary attachments and files over 1 MB are rejected with an error. Attachment paths recorded in results.json that escape workingDirectory (via .. or absolute paths pointing elsewhere) are refused.

list_tests

Lists all tests with their spec file and tags without running them.

Input	Type	Description
workingDirectory	string (optional)	See Multi-worktree support. Defaults to ".".
tag	string (optional)	Filter by tag, e.g. @smoke

---

Attachments

Playwright attaches files to failed tests automatically. get_test_attachment can read any text attachment by name.

Attachment name	Source	Present in every project
error-context	Playwright built-in — YAML accessibility tree snapshot at the point of failure	Yes
screenshot	Playwright built-in — PNG screenshot (binary, not readable)	Yes
video	Playwright built-in — WebM video (binary, not readable)	Yes
Custom attachments	Added via testInfo.attach() in your fixtures	Depends on project

The error-context attachment is the most useful for projects without custom fixtures — it gives a semantic, structured view of the page at the moment of failure with no setup required.

---

Installation

Via npx (recommended) — use the npx config shown in Quick start. No local installation needed.

From source:

git clone https://github.com/hubertgajewski/playwright-report-mcp.git
cd playwright-report-mcp
npm install
npm run build

---

Configuration

Add to your .mcp.json at the root of your project:

{
  "mcpServers": {
    "playwright-report-mcp": {
      "command": "npx",
      "args": ["-y", "playwright-report-mcp"],
      "type": "stdio"
    }
  }
}

Environment variables

Variable	Default	Description
PW_ALLOWED_DIRS	"." (authorizes only the launch dir)	path.delimiter-separated list of directories the workingDirectory parameter may point at. Entries may be absolute or relative (resolved once against launch cwd at startup).
PW_RESULTS_FILE	<workingDirectory>/test-results/results.json	Absolute path to the JSON reporter output file. If set, overrides the per-call default for every call.

Set PW_RESULTS_FILE if your playwright.config.ts writes the report to a non-default location. Leave it unset in multi-worktree setups so each workingDirectory gets its own test-results/results.json.

Multi-worktree support

run_tests, list_tests, get_failed_tests, and get_test_attachment all accept an optional workingDirectory parameter — absolute, or relative to the MCP server's launch directory. This lets a single long-lived MCP session drive tests across multiple git worktrees without restarting.

Because a Playwright config is a Node module that executes on playwright test startup, the server guards the parameter with an allowlist. Callers that point workingDirectory at a directory outside PW_ALLOWED_DIRS get a structured error and no child process is spawned.

Default (no worktrees). Leave PW_ALLOWED_DIRS unset. The allowlist becomes "." — only the launch directory — and the default workingDirectory (also ".") resolves to the launch directory. Zero configuration.

Sibling worktrees. Set PW_ALLOWED_DIRS=".." in your .mcp.json to authorize every sibling of the launch directory. Relative entries resolve against the launch cwd at startup, so the same .mcp.json works for every contributor without baking in absolute paths:

{
  "mcpServers": {
    "playwright-report-mcp": {
      "command": "npx",
      "args": ["-y", "playwright-report-mcp"],
      "env": { "PW_ALLOWED_DIRS": ".." },
      "type": "stdio"
    }
  }
}

Then point calls at any sibling worktree:

{
  "name": "run_tests",
  "arguments": { "workingDirectory": "../my-app-feat-auth" },
}

Multiple projects. Either launch the MCP client from each project and use the default allowlist, or set PW_ALLOWED_DIRS to the shared parent and pass workingDirectory per call. The allowlist check runs at a path-segment boundary, so an entry authorizing /src/my-app will not authorize /src/my-app-evil.

Breaking change (2.x → next): the PW_DIR env var has been removed. Either launch the MCP client from inside the Playwright project directory (zero-config, default workingDirectory: "." works), or pass workingDirectory per call and set PW_ALLOWED_DIRS accordingly.

---

Requirements

• Node.js 22+
• @playwright/test 1.40 or later
• JSON reporter configured in your Playwright project

Playwright's default reporters (list locally, dot on CI) write to stdout only — they produce no file that can be read after the run. Add the JSON reporter alongside whatever reporters you already use:

// playwright.config.ts
reporter: [
  ['json', { outputFile: 'test-results/results.json' }],
  ['html'],  // keep any existing reporters
  ['list'],
],

---

Troubleshooting

No results.json found — run tests first

The JSON reporter is not configured or is writing to a different path. Verify your playwright.config.ts has ['json', { outputFile: 'test-results/results.json' }].

list_tests parsed 0 tests from non-empty output

The --list output format may have changed in your version of Playwright. Open an issue with your Playwright version and the raw stdout output.

Attachment "..." is binary and cannot be returned as text

screenshot and video attachments are binary files. Use get_failed_tests to get attachment paths and open them directly if needed.

Attachment "..." is too large to return inline

The attachment exceeds 1 MB. Read the file directly from the path returned by get_failed_tests.

---

Development

npm test          # run tests once
npm run test:watch  # watch mode

Tests use Vitest and cover the collectSpecs helper (unit) and all four MCP tools via InMemoryTransport (integration). No build step or Playwright installation required to run the test suite.

---

Cutting a release

Releases are produced by pushing a v* tag. .github/workflows/release.yml picks up the tag, verifies the tag matches all three version fields, runs npm ci + npm run build + npm test, creates a GitHub Release with auto-generated notes categorized per .github/release.yml (Features / Bug fixes / Documentation / Dependencies / Other changes), and publishes to npm. .github/workflows/publish-mcp.yml then chains off Release via workflow_run and publishes server.json to the MCP registry. Merging to main does not trigger a publish.

Version lives in three places and all three must match the tag before pushing it:

• package.json → version
• server.json → top-level version
• server.json → packages[0].version

Bump all three in one PR and merge to main before cutting the release. release.yml fails the run if the tag disagrees with any of these values.

Ritual:

# After the version-bump PR has merged to main:
git checkout main && git pull
git tag v1.0.5
git push origin v1.0.5
# → release.yml fires: verifies tag, builds, tests, creates GitHub Release, publishes to npm
# → publish-mcp.yml chains off Release and publishes server.json to the MCP registry

Flow:

1. Open a bump PR that updates all three version fields. Merge it to main.
2. Tag the bump commit v<version> and push the tag.
3. release.yml verifies tag/version alignment, runs npm ci, confirms the version is not already published on npm, runs npm run build + npm test, creates the GitHub Release, then publishes to npm with npm publish --access public --provenance.
4. publish-mcp.yml (triggered by workflow_run on Release) re-verifies the version fields, confirms the version is not already on the MCP registry, and publishes server.json to registry.modelcontextprotocol.io.

No repository secrets required. Both npm and the MCP registry authenticate via GitHub OIDC (npm trusted publishers). The trusted publisher for npm is configured on npmjs.com under the package's Settings → Publishing access → Trusted Publisher section — no NPM_TOKEN secret exists or is needed.

Recovery from a failed publish: npm refuses to republish an existing version and restricts unpublishing after 72 hours. If a publish fails for any reason, bump to the next patch version in a new PR and cut a new release — do not try to re-run the failed release.

---

Contributing

See CONTRIBUTING.md for bug reports, pull requests, development setup, and commit conventions.

---

License

MIT — Copyright (c) Hubert Gajewski