Iurii Uses: #SaaS

kri.rocks – Booking Website and Online Scheduling SaaS for Beauty Businesses

Vertical SaaS that gives a salon, barbershop or solo beauty specialist their own booking website in minutes.

HTPBE.TECH – Internal Admin Dashboard

Role-gated admin dashboard for the HTPBE? SaaS platform – real-time KPIs, per-user quota tracking, and a zero-dependency bar chart.

vatnode.dev – EU VAT Validation API

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

HTPBE.TECH – Has This PDF Been Edited?

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

Vertical SaaS vs horizontal SaaS: separate audience from configurability, cut MVP scope with shared workflows, and skip unnecessary launch complexity.

Prevent double booking in PostgreSQL without UNIQUE or EXCLUDE: advisory locks, an overlap check, and when EXCLUDE is the right choice.

Compare marketplace fees with a booking website using avoidable costs, retained acquisition, and a worked example of when switching saves money.

Booking slots across daylight saving time: why isValid misses skipped times and why a pinned version cannot resolve autumn ambiguity.

Race condition testing with real PostgreSQL: readiness gates, observed lock waits, provider stubs, and the false confidence a timed assertion can give.

Run next/image on a self-hosted VPS without OOM: why the optimizer is memory-hungry, how to bound device sizes, formats, and cache, or offload it.

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

Prevent overselling under concurrent checkouts: reservations vs hard decrements, SELECT FOR UPDATE, deadlock-safe multi-line carts, and the payment window.

Subscription billing edge cases Stripe glosses over: proration, dunning, the state machine, cancellation timing, refunds, VAT, and webhook ordering.

Feature flags without LaunchDarkly: a Postgres-backed, ~100-line system with deterministic percentage rollout, per-tenant overrides, and caching.

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

Build an internal CRM on Supabase: schema, RLS policies, Next.js App Router frontend, realtime subscriptions, and an honest look at where the weekend ends.

Multi-tenant SaaS database design: shared schema with RLS, schema-per-tenant, and database-per-tenant – trade-offs, real pitfalls, and when to use each.

Headless CRM comparison 2026: Twenty vs EspoCRM vs DIY on Postgres. Real trade-offs on schema flexibility, integration, cost, and ecosystem risk.

PostgreSQL production patterns: UUID v7, soft deletes, RLS for multi-tenant SaaS, partial and covering indexes, PgBouncer pooling and migration discipline.

BullMQ vs pg-boss vs node-cron for Node.js background jobs. Trade-offs between Redis and Postgres queues, retries, deduplication, and production monitoring.

JWT vs sessions vs OAuth for SaaS: token invalidation, mobile clients, refresh token rotation, and a decision matrix to pick the right auth pattern.

MVP features that kill products before launch: roles, notifications, dashboards, multi-tenancy, onboarding. What to cut and what matters at launch.

AI document processing in production: full PDF pipeline – OCR fallbacks, structured output, validation, cost at scale. Beyond naive GPT calls.

Add AI to an existing product without a rebuild. Three integration patterns, how to pick the right one, and what production-ready AI actually demands.

Real-time Next.js admin dashboard: TanStack Query polling, Zustand for filter state, Sentry error boundaries per panel, and a zero-dependency bar chart.

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.

Next.js view counter with Upstash Redis over HTTP: atomic INCR, Edge Runtime for zero cold starts, React Strict Mode fix, and slug namespace gotchas.

UUID v7 vs v4 in PostgreSQL: why random UUIDs fragment B-tree indexes, how UUID v7 fixes it, benchmarks at 5M rows, and Drizzle ORM migration steps.

EU VAT validation in Next.js: VIES caching with Redis, three-state results, reverse charge logic, and audit logging – what actually works in production.

40+ point production SaaS checklist: auth, Stripe billing, PostgreSQL, rate limiting, email, monitoring, and security – with honest 8-week build estimates.

Stripe webhook production architecture: idempotency keys in PostgreSQL and Redis, a BullMQ queue, and signature verification in Next.js App Router.

Detect tampered PDFs using xref table analysis, metadata mismatches, orphaned objects, and font changes – 7 forensic markers explained with TypeScript code.

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

Turborepo monorepo with Next.js and Hono, sharing one set of TypeScript types across frontend and backend.