Iurii Uses: #API

vatnode — EU VAT Validation API

Developer-first SaaS API for EU VAT validation via VIES with Redis caching, change monitoring, and webhook notifications.

HTPBE? — Has This PDF Been Edited?

SaaS platform for PDF authenticity verification with a public REST API.

WebSocket reconnection for production: heartbeat dead-connection detection, exponential backoff with jitter, resubscription, and message replay.

API key management for a public SaaS: hashing keys at rest, prefix + last-4 display, fail-closed validation, and revocation — plus the scoping, rotation, and

Webhook security past the signature: replay attacks, payload trust, DoS, IP allow-listing, and secret rotation — what verification does not protect.

Idempotency key API design: make POST retries that don't double-charge — Postgres key table, ON CONFLICT claim, response replay, TTL, edge cases.

Self-host a Node.js API on a €6/month VPS: Caddy reverse proxy, Docker Compose, zero-downtime deploy script, and GitHub Actions CI — complete production setup.

Redis rate limiting for APIs: sliding window ZADD with Lua atomicity, in-memory fallback, multi-tier limits by IP and API key, and developer-friendly response