PixelCheck

Real eyes and hands for the AI agent that's writing your frontend.

Drop-in MCP server. Five browser primitives. Eighteen personas across fifteen countries.
Local-first · Vendor-agnostic · MIT-licensed · Yours to own.

Quick Start →  ·  Primitives  ·  MCP Server  ·  Audit Preset  ·  Why Not E2E  ·  Changelog

If PixelCheck helps you, give it a star — it helps others discover the project.

Right now, you're a screenshotting middleman.

Your AI agent is writing 80% of your frontend. It's fast. It's good at code. But it's blind.

• It writes a button. You open Chrome to check it rendered right. Paste a screenshot back. Ask for the fix.
• It tweaks the OAuth flow. You log in to verify it didn't silently break. Again. Sixth time this month.
• It updates the Japanese strings. A user emails: "half the page is in English." You didn't catch it.
• It rewrites checkout. You walk through it on iPhone, Android, iPad just to feel whether step 3 is confusing.
• It changes the Arabic layout. RTL didn't propagate. You don't notice for two days.

You become the bridge. The agent has thoughts. You have a browser. The two never meet. Hours of your week, every week, indefinitely.

PixelCheck is the bridge.

A single MCP server. Five primitives. Drop it in once — your agent has eyes and hands.

see(url, opts)              snapshot a page (DOM + screenshot + console + network)
act(url, steps)             execute an action sequence (semantic + selector + Computer Use)
extract(url, schema)        pull structured data matching a Zod / JSON schema
judge(url, rubric)          score a page against a rubric ("is this dark-pattern free?")
compare(a, b, criteria)     A/B comparison of two URLs (incl. blind mode)

Now your agent navigates. Sees rendered HTML. Reads console errors. Clicks. Fills. Judges. Compares. Without ever leaving its workflow — drop into Claude Desktop, Cursor, Cline, Continue, Zed, or Claude Code via four lines in ~/.mcp.json.

npm install -g pixelcheck        # browser binary auto-installs on install
pixelcheck doctor                # verify environment (--fix self-heals)
pixelcheck-mcp                   # MCP server (stdio transport)

// ~/.mcp.json
{
  "mcpServers": {
    "pixelcheck": {
      "command": "pixelcheck-mcp",
      "env": { "ANTHROPIC_API_KEY": "sk-ant-..." }
    }
  }
}

Restart your client. Your agent has eyes.

Three promises that aren't going anywhere.

Local-first. PixelCheck runs entirely on your machine. The only outbound network destination is the LLM provider your agent already uses. Screenshots, DOMs, business flows, OAuth tokens, customer URLs — they stay yours. Zero telemetry. Zero remote storage. Zero SaaS sign-up. The audit data hits Anthropic only when the vision critic actively scores a screenshot, and you opt in once on first run.

Vendor-agnostic. Works with Claude today; multi-provider abstraction (OpenAI, Gemini, Ollama-local) is on the v1.x roadmap and your agent will switch with one config flag. The reason is simple: AI tools that lock you to a single LLM provider die in 2026. PixelCheck is the antidote.

Yours to own. MIT license. Source-available. No paid tier. No "Pro" upgrade path. No commercial fork waiting in the wings. The 1858-test, 29-ADR, 30-published-schema product in this repo is the entire product. There's no premium edition behind a sign-up wall — never was, never will be.

The Audit Preset — when you want to be the user, not the bridge

The five primitives compose into something more powerful when you're the operator: PixelCheck bundles an 18-persona / 15-country audit preset on top of the primitives — a CLI-first composition that runs "eighteen real users review your product" after every deployment.

You deploy. Tests pass. CI is green. But then:

• A Japanese user opens your app and sees half-translated English strings mixed into the UI
• A user on a budget Android phone in Nigeria waits 12 seconds for your hero image to load
• Your OAuth login flow silently breaks — again — for the 6th time in 10 deployments
• The Arabic version renders left-to-right, making the entire layout unusable
• Your "Trusted" score badge shows green while the copy says "stop interacting immediately"

No E2E test catches these. They test whether code runs. They don't test whether the product works for real humans in real contexts.

The audit preset launches real Chromium browsers as 18 different users from 17 countries, walks through your product's core flows, and delivers a verdict — like having a senior PM, QA engineer, and UX reviewer audit every deployment, in every language, on every device class.

pixelcheck init projects/my-app --name "My App" --url "https://myapp.com"
pixelcheck run --project projects/my-app

Output: a structured report with per-step screenshots, video recordings, network logs, WCAG accessibility violations, and AI-scored ratings across 6 dimensions — served as JSON, HTML dashboard, or Markdown.

How It Works

For each (persona x scenario) combination:

 1. Launch Chromium with device-accurate fingerprint
    (viewport, locale, timezone, UA, regional proxy)
                        |
 2. Execute scenario steps semantically via Stagehand 3.x
    ("click the sign-up button" not "click #btn-37")
                        |
 3. 5-Layer Reliability Stack ensures 98%+ step success
    Stability Gate -> LLM Rewrite -> Selector Discovery -> Auto Selector -> Computer Use
                        |
 4. Claude Vision Critic + axe-core score each checkpoint on 18 dimensions
    completion | localization | visual_polish | trust_signals | accessibility | ...
                        |
 5. Critical steps escalate to Computer Use for pixel-level review
                        |
 6. Generate report: JSON + HTML dashboard + Markdown + video + HAR

Why Not E2E Tests?

PixelCheck's audit preset is not a replacement for E2E tests. It's what runs after them — the layer between "code works" and "product is good."

Compared to existing tools