Portfolio

Real systems, real numbers — every case study ends with a measurable result

12 case studies

18,000+ orders in systems

2 deployment countries

Company AI knowledge base — a „brain" for a security firm

An internal company brain for an alarm monitoring station (~150 sites): an operator chat that answers step-by-step from the firm's own procedures (RAG, with source citation), an editable knowledge base with AI-assisted procedure drafting, and a model swappable in one click (Claude/ChatGPT/Gemini) — no vendor lock-in. Working demo deployed in 1 day.

Next.jsTypeScriptClaude AIRAGOpenAIGeminiVercel

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Case Study

Legacy Rescue — abandoned 8-year-old backend

Modernization of an abandoned internal system for a multi-location retail business. Java Spring Boot backend rewritten to Node.js while keeping the React 15 frontend untouched. 21 contract items delivered 100%, zero-downtime database migration, own auth (bcrypt + JWT), HTTPS via Caddy.

Node.jsExpressMySQLReact 15JWTbcryptCaddy

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Case Study

Payout engine — silent failures fixed at scale

A browser-side payout flow silently half-completed an 18,080 CHF / 212-record run. Rebuilt with bulk operations (~272 HTTP calls → ~10), a payout state machine, nightly audit + Telegram alerts and one-click recovery. 210 records: ~126s (failing) → 3.9s.

Base44DenoTypeScriptReactTelegram API

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Case Study

Studio Manager — System Rescue

Fixed critical bugs in a no-code platform: payment vulnerability (multiple withdrawals), Telegram webhook limits (external microservice on Deno Deploy), OAuth security gap (3-tier RBAC), tax logic errors.

SupabaseDenoOAuthRBACTelegram API

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Case Study

Production migration — unsupported server → reliable cloud

Migrating a live company system off an outdated server (end-of-life Ubuntu, no HTTPS, no backups) onto cloud infrastructure. 14-minute weekend cutover, HTTPS via Caddy, daily off-site backup in a second country with a verified restore, one week of supervision.

Hetzner CloudUbuntu 24.04CaddyLet's EncryptDockerrclonePM2

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Case Study

Dental Scheduling SaaS — multi-tenant booking that can't double-book

Multi-tenant dental booking core: strict RLS tenant isolation, atomic double-booking prevention via a Postgres partial index, live availability (Broadcast), and reserve-before-Stripe payments with an idempotent webhook. Verified 9/9 end-to-end against production. Live demo + open source.

Next.js 14TypeScriptSupabasePostgreSQLRLSStripe

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Case Study

Accommodation MVP — rooms for construction crews in Germany

A narrow MVP built after a lead went cold: construction ZIP code → nearby rooms from monteurzimmer.de, filters by price, distance and living conditions, German inquiry template and safe test sending through Resend. Live demo on a custom domain.

Next.js 14TypeScriptTailwind CSSResendVercel

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Case Study

Studio Manager — when fixing one bug surfaces eleven more

A compliance email bug surfaced three layers of hidden data quality issues: 11 historical records (client knew of 4), 2 platform bugs, a fundamental UX trap in the panel (empty field rendered as "no"). 5 promised items + 50% discovery scope.

Base44Deno DeployWebhooksResendCompliance

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Case Study

AI lead analysis — 100 job ads in 2 minutes

3-phase system analyzing OLX job postings: rule-based pre-filter eliminates 70% of noise, Claude Haiku scores automation potential and trigger score, Sonnet drafts personalized outreach. 100 postings in 2 minutes for under $0.30.

PythonClaude AIHaikuSonnetJinja2HTTP API

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Case Study

AI Consultation System — two-tier funnel

Two-tier AI consultation system: free qualification (Claude Haiku) + premium technical analysis for 200 PLN (Claude Opus). Stripe, Supabase, Resend integration. Context continuity between sessions, JSON summaries, transactional emails.

AstroClaude AIStripeSupabaseResendTypeScript

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Case Study

DRM Video Player — streaming platform rebuild

Web video player for a hybrid live/VOD platform: a standalone module immune to CMS updates, adaptive HLS/MPEG-DASH streaming, multi-audio, subtitles, watermark and a full cross-browser matrix. Stage 2: a DRM pipeline (Widevine, PlayReady, FairPlay) with a license proxy that survived several KMS provider swaps without touching the player.

HLSMPEG-DASHMSEEMEWidevinePlayReadyFairPlay

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Case Study

Asystent — salon appointment app (Android)

Native Android app for a beauty salon (MVP): client database (name, phone, e-mail) and an automatic e-mail reminder one hour before each appointment. Local SQLite, WorkManager for reboot-safe background jobs, SMTP delivery configured in-app. Delivered: APK + guide + full source code.

KotlinAndroidSQLiteWorkManagerSMTP

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Case Study

Probability grid — data analysis of star-cluster simulations

Bachelor's thesis (statistics & data analysis): a statistical probability grid of dynamical interactions built from ~460k CMC interactions. Configurable Python pipeline (ingest → filters → 16 grids 20×20×20×20 → get_probability API), type-pair symmetrization, adaptive bins, 10k-sample round-trip validation. Thesis accepted by the advisor; code being integrated into binary_c.

PythonNumPypandasParquetMatplotlibJupyterpytest

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