parcel-router01 / 06
Deterministic carrier routing
34% → 6%
Portfolio — 2026Grenaa, Denmark · remote Available for work
Senior Backend Engineer · Logistics & parcel SaaS
WladyslawCzeresniowski
I build logistics backends that move parcels, money, and freight — Python/Django systems, carrier integrations, Postgres-heavy workflows, and Rust/Go workers where performance matters.
I build the event-driven backends that move money — price streams, courier integrations and reconciliation, and the automatic refunds that have to be boring in production.
By the numbers 01 / 05
34% → 6%
mis-route rate — the carrier-routing engine on cost, SLA, and live capacity, against the hand-tuned rules it replaced, in a reproducible benchmark.
~26×
lower p99 task time after rewriting the Django/Celery queue worker in Rust — the headline of the migration write-up.
8M
freight rate-quotes priced a day by the Go rating service; its committed load test sustains ~46k req/s, far above that.
<40ms
freight rate-quote p99 in the Go rating service — its load test measures ~11 ms at ~46k req/s, well inside the 40 ms budget.
0
double-refunds in two years of an idempotent pipeline.
01
Selected work
Systems I have shipped
freight-rating02 / 06
Freight-quote rating service
p99 < 40ms
skip-locked03 / 06
Postgres as a job queue
one table
refund-engine04 / 06
Idempotent refund pipeline
no double refunds
idem-key05 / 06
Idempotency keys, done once
Rust + Go
pg-outbox06 / 06
Transactional outbox
same-tx
02
Experience — Twelve years building backend systems
2024 — nowCurrently
Founder & Backend Engineer
remitto.io · NestJS · Temporal · Postgres
- Built the carrier-claim recovery engine as a durable Temporal workflow — detect the SLA breach, file the claim, reconcile the payout — idempotent at every step so a retry never double-claims.
- Shipped it solo: Next + Nest on Vercel and Fly.io, WorkOS auth, CI/CD from day one.
- The same invariants run in a public companion repo: ~12,000 owed refunds auto-recovered in one pass, 0 double-refunds — reproducible yourself, not a dashboard I can't show you.
~12krefunds recovered / run
0double-claims
1person shipped it
Idempotent refund state machine
2018 — nowCurrently
Backend Engineer (contract)
Self-employed · logistics · Python · NestJS · Kubernetes
- Normalized 40+ courier APIs behind one internal contract, with retries, backoff, and circuit breakers around every flaky upstream.
- Reconciled payments, surcharges, and invoices into idempotent ledgers — a replayed webhook never double-charges.
- Backed the routing and rating hot paths with reproducible benchmarks in companion repos: <40ms p99, ~46k req/s sustained, runnable yourself.
40+courier APIs
<40msrating p99
~46kreq / s
Carrier routing engine
2015 — 2018
Backend Engineer
Rise & Raise · Django · Node · Postgres
- Collapsed a dozen exchanges and terminals into a single normalized live price stream.
- Drove everything off events — price moves fired the jobs, no polling loops to fall behind.
- Kept the stream honest under bursty load with idempotent event handling.
1live price stream
liveevent prices
0polling loops
Live price-stream aggregator
04 — Get in touch
Open to senior & principal backend roles
Get in touch.
If you are hiring for a senior or principal backend role in logistics, payments, or anything high-throughput, email me. One honest reply, no recruiter funnel.
wladyslaw@czeresniowski.devBased in Grenaa, Denmark · remoteReplies within a dayAvailable now
GitHub ↗LinkedIn — soon