A SaaS for keeping an eye on competitors: on a schedule it downloads their pages, compares them with earlier snapshots by headings, links and prices, and writes a short Russian summary of what changed with an LLM.
What is inside
- Pipeline — fetch → extract → diff → summarize. Snapshots and changes are stored apart from the summaries, so a diff can be recomputed without calling the LLM again.
- Entity diffs — comparison over the headings, links and prices that were extracted, not over raw HTML; the price chart and change history are built from the same rows.
- Scheduler — APScheduler inside the FastAPI lifespan, plus a manual “Check now” with a cooldown and protection against overlapping runs.
- Billing — YooKassa: a plan is raised only by the
payment.succeededwebhook, and the payment status is re-fetched from the API rather than trusted from the notification body. Plan limits (free / pro / business) are enforced at the endpoint level. - SSRF guard — a competitor accepts only absolute http(s) URLs; loopback and private hosts are rejected before the fetcher ever sees them.
- 35 pytest tests — auth, billing, CRUD, scheduler, pipeline and the guard, against a throwaway Postgres via testcontainers.
Stack
FastAPI + SQLAlchemy + Alembic + PostgreSQL 16 on the backend, Next.js 15 (App Router, TypeScript) and Tailwind on the frontend. The fetcher is httpx + BeautifulSoup with no Playwright: the service has to fit in 2 GB of RAM on a VPS. Docker Compose throughout, nginx and certbot in production.
Demo
rivalens.ru — the production VPS. Sign-up is required: a new account is seeded with a demo competitor so it never opens on an empty screen.