Backend Developer · London / Remote

Jakub Lesniak

Backend developer in London. I've been coding for about a year and a half, mostly Python and FastAPI. Here are three projects I've built and put online — have a look.

View work GitHub LinkedIn
Banking API· Virus Simulation· Chess Engine

Selected work

Projects

All three are deployed and you can try them live. Here's what each one does, and the kind of request it handles.

01 — Financial transactions

Banking API v2

A REST API for basic banking.

Register a user, open an account, move money between accounts. Auth is handled with JWT. Balances are stored as integers (pence) so there are no rounding errors, and transfers run inside a database transaction, so if something fails it rolls back instead of leaving a half-finished transfer. There are user and admin roles.

FastAPIPostgreSQL SQLAlchemyJWT · HS256 Docker
Live demo → Source →
transfer.http
POST /transactions/transfer/{account_id}
Authorization: Bearer <jwt>

{ "amount_pence": 5000 }

200 OK
{
  "status": "complete",
  "amount_pence": 5000,
  "sender_balance": 12750
}
02 — Data-driven simulation

Virus Spread Simulation

Simulates how a virus spreads through a country.

You give it a country and a virus, and it runs a day-by-day simulation based on a SIR model. It pulls live weather and air-quality data, mixes in population density and healthcare figures, and uses that to adjust how fast the virus spreads and how deadly it is. You can run two countries side by side. It has a test suite.

FastAPIPostgreSQL SQLAlchemyrequests pytestDocker
Live demo → Source →
simulate.http
POST /sim/Brazil/COVID-19/30

200 OK
{
  "country": "Brazil",
  "temp_factor": 0.94,
  "density_factor": 0.71,
  "healthcare_score": 0.62,
  "day_30": {
    "infected": 184203,
    "recovered": 91022,
    "dead": 3677
  }
}
03 — Engine integration

Rordon Gamsey Chess

Play chess against Stockfish. It roasts you.

A chess app built around the Stockfish engine. After each move it checks how much your position got better or worse and picks one of 399 roast lines to throw at you, read out loud. Each game runs in its own session, so different players don't end up sharing the same board.

FastAPIStockfish python-chessThreading TTS audio
Live demo →
move.http
POST /move

{ "from": "e2", "to": "e4" }

200 OK
{
  "engine_move": "c7c5",
  "eval": -0.3,
  "tier": "backhanded",
  "roast": "Bold. Stockfish is unbothered."
}

About

I'm self-taught, and I've been coding for about a year and a half.

I'm a backend developer in London. I work mostly in Python — FastAPI, PostgreSQL, SQLAlchemy and Docker — and I like working on APIs, databases and auth.

I'm looking for my first job as a backend developer.

AWS AWS Certified Cloud Practitioner · Issued Jun 2026 · Verify

Skills

What I work with.

Languages & Frameworks

  • Python
  • FastAPI
  • SQL
  • C (foundations)
  • REST API design

Data & Infrastructure

  • PostgreSQL
  • SQLAlchemy ORM
  • Docker & Compose
  • AWS Certified (Cloud Practitioner)
  • Render deployment

Engineering Practice

  • JWT authentication & RBAC
  • Atomic transactions
  • pytest
  • Git & GitHub
  • API documentation

Contact

Get in touch

I'm looking for my first backend developer role, in London or remote. Email is the easiest way to reach me.

Email me GitHub LinkedIn