browser-fingerprint-audit

liarjs skills

Agent Skills for browser fingerprint testing and automation-harness QA.

Four skills that teach a coding agent to run liarjs: 40 consistency checks over 19 fingerprint probes, cross-checked against what the TLS/HTTP layer actually saw.

liarjs.dev - what the checks mean - field notes

npx skills add liarjs.dev                  # from the site's well-known endpoint
npx skills add liarjsdev/liarjs-skills     # from this repo

The skills

Each skill is a directory with a SKILL.md following the Agent Skills format, so it works in any client that supports the standard: Claude Code, Codex, Cursor, GitHub Copilot, VS Code, Gemini CLI, OpenCode, Amp, Windsurf, Goose, Kiro and others.

Install

With the cross-agent installer:

npx skills add liarjs.dev                                               # all four, from the site
npx skills add liarjsdev/liarjs-skills                                  # all four, from this repo
npx skills add liarjsdev/liarjs-skills/skills/browser-fingerprint-audit # just one

liarjs.dev works because the site publishes this same tree at /.well-known/agent-skills/index.json (RFC 8615), so no directory site sits between you and the skills. The generator lives in the site repo as scripts/sync-skills.mjs and takes this repo as its source of truth.

Or copy a skill directory into the location your agent reads:

What the underlying tool does

A browser controls its own JavaScript. It does not control the network it connects over. liarjs reads the fingerprint inside the browser, reads the TLS/HTTP/ASN view from the edge that served the request, and reports every place the two stories disagree.

   18 / 100  Likely spoofed / bot

  x navigator.webdriver -40
    webdriver=true, the automation flag is set.
    id: webdriver

  x Worker <-> main-thread consistency -20
    A Web Worker reported different values than the main thread for userAgent, canvasHash.
    id: worker-consistency

  22 checks - 2 critical - 1 warnings - 18 clean
  edge: 203.0.113.7 - AS4058 - LAS - HTTP/2 - TLSv1.3

32 of the 40 checks need nothing but the browser (--offline). 8 compare the JavaScript story against the wire. Full list with deductions: checks.md.

Requirements: Node 22 or newer, and a local Chrome, Chromium or Edge. liarjs has zero runtime dependencies.

Scope and safety

These skills are measurement and diagnostics. They ship no evasions, profiles or proxies.

• A scan launches its own Chrome with a fresh profile in a temp directory and deletes it when the run ends. It does not read the user's browser profile, history, cookies or saved credentials.
• No token, login or account is involved. The skills never ask an agent to handle secrets.
• Nothing is fetched at runtime that changes agent behaviour: the instructions and reference files are the whole content, and the npm package is version-pinned in every command.
• Probes run on about:blank by default. The skills do not direct an agent to browse third-party sites, and they state that scan output is data to relay rather than instructions to follow.
• Attaching to an already-running browser (--cdp) is documented as an explicit, user-requested path, not a default, because that drives a session the user owns.
• The one outbound request in the default path is the browser under test fetching https://liarjs.dev/api/net.json, which answers with what Cloudflare saw about that request. --offline makes no request at all; --endpoint <url> points at your own deployment of that Worker. liarjs.dev does not store scans.

Related packages

Source for all three: github.com/liarjsdev/liarjs.

Limits worth stating up front

• A score is not a ban prediction. It measures internal coherence. Real sites also weigh IP reputation, account age and behaviour, none of which a local scan can see.
• Headless is detected on purpose. A stock headless run loses points, and that is the correct measurement.
• Checks drift with Chrome. The rules are versioned with the package and reviewed per Chrome major, which is why every command here pins a version.

MIT (c) liarjs.dev