{"slug": "stop-letting-your-coding-agent-claim-pixel-perfect-make-it-prove-97-49", "title": "Stop letting your coding agent claim \"pixel-perfect\". Make it prove 97.49%.", "summary": "A developer built hwatu, a browser designed for coding agents to verify UI changes via pixel diffing, achieving a 97.49% match in about 87 ms per verification loop. The tool runs headlessly on Linux using WebKitGTK, supports CLI and MCP integration, and aims to replace blind 'pixel-perfect' claims with measurable proof.", "body_md": "Your coding agent edits a component, runs the build, and reports the UI is now \"pixel-perfect.\" It never opened a browser. It's guessing.\n\nI got tired of that, so I built [hwatu](https://github.com/hongnoul/hwatu), a browser designed specifically for the agent verification loop.\n\n```\nhwatu --headless http://localhost:3000   # open, no focus steal\nhwatu wait-load                          # block until loaded\nhwatu eval 'document.title'              # DOM-level checks\nhwatu shot /tmp/check.png                # screenshot\nhwatu diff --id 1 --baseline before.png  # pixel diff: 97.49% match + heatmap\nhwatu close 1\n```\n\nThe whole loop, screenshot included, runs in about 87 ms on my laptop. Cheap enough that the agent can verify after every edit instead of claiming success blind.\n\n`webkitgtk-6.0`\n\n. No 170 MB download per project.`hwatu mcp`\n\n), plain CLI, and a 1-line JSON socket. Works with Claude Code, Cursor, Jcode, or any harness.Every benchmark in the repo was measured on real runs with scripts you can rerun: window spawn medians of 13-16 ms, ~87 ms full verification loop, memory measured via PSS across all WebKit child processes. Methodology in [docs/benchmarks.md](https://github.com/hongnoul/hwatu/blob/main/docs/benchmarks.md).\n\n```\ncurl -fsSL https://raw.githubusercontent.com/hongnoul/hwatu/main/scripts/install.sh | bash\nhwatu setup   # detects Claude Code, Cursor, Jcode, or generic MCP\n```\n\nMIT licensed. Linux (WebKitGTK). Feedback and issues welcome: [https://github.com/hongnoul/hwatu](https://github.com/hongnoul/hwatu)", "url": "https://wpnews.pro/news/stop-letting-your-coding-agent-claim-pixel-perfect-make-it-prove-97-49", "canonical_source": "https://dev.to/hongnoul/stop-letting-your-coding-agent-claim-pixel-perfect-make-it-prove-9749-f4f", "published_at": "2026-07-25 09:31:44+00:00", "updated_at": "2026-07-25 10:31:53.091229+00:00", "lang": "en", "topics": ["developer-tools", "ai-agents", "computer-vision"], "entities": ["hwatu", "WebKitGTK", "Claude Code", "Cursor", "Jcode"], "alternates": {"html": "https://wpnews.pro/news/stop-letting-your-coding-agent-claim-pixel-perfect-make-it-prove-97-49", "markdown": "https://wpnews.pro/news/stop-letting-your-coding-agent-claim-pixel-perfect-make-it-prove-97-49.md", "text": "https://wpnews.pro/news/stop-letting-your-coding-agent-claim-pixel-perfect-make-it-prove-97-49.txt", "jsonld": "https://wpnews.pro/news/stop-letting-your-coding-agent-claim-pixel-perfect-make-it-prove-97-49.jsonld"}}