Sentinel: an open-source QA agent that reads your code before it clicks

Show HN: Sentinel – open-source QA agent that reads your code before it clicks

SimbaStack open-sourced Sentinel under MIT, a QA agent that reads the codebase first, derives business flows on its own, then tests them end-to-end across frontend and backend. They pointed it at their own hotel PMS with only the repo and admin credentials, no test plan. Sentinel read the code, concluded it was a boutique hotel system, and auto-derived nine critical flows including the full reservation lifecycle, group bookings, and night audit. It ran the top two flows twice each and caught three bugs invisible to UI-only checks: a backend NO_AVAILABILITY error on a reservation that already held the room, a calendar showing a room as available when the API said it was booked, and a check-in returning 200 but leaving the guest registration status unchanged. The pipeline: a deterministic grep/find recon pass extracts code structure, Xiaomi's Mimo model derives business flows, Playwright drives the browser, and an api_request tool checks server state. Each flow runs twice by default, findings are unioned, and a 90-call cap bounds each attempt. A final vision pass scores visual hierarchy, spacing, and contrast on visited screens. It currently supports common JS stacks like Next.js, Express, Fastify, and Prisma; other stacks need a recon patch.

Why it matters: A new entrant in the open-source QA agent space with a real end-to-end experiment on a hotel PMS — not a toy demo. Score stays below 80 because there's only one blog post so far, no third-party reproduction or head-to-head comparison yet.