parcel-router01 / 04
Deterministic carrier routing
A routing engine that picks the right courier across 40+ regional carriers from cost, SLA, and live capacity — replacing a pile of hand-tuned rules. Mis-routes dropped 60%.
Portfolio — 2026Grenaa, Denmark · remote Available for work
Senior Backend Engineer · Logistics & parcel SaaS
WladyslawCzeresniowski
I build the backend that moves parcels and freight — carrier routing, integrations, and the high-throughput systems behind them, in Rust and Go.
I build the backend that moves parcels and freight at scale — carrier routing, integrations, and the high-throughput systems that have to be boring in production.
By the numbers 01 / 05
60%
fewer mis-routes after the carrier-routing rewrite.
11×
faster p99, after migrating the hot path from Python to Rust.
8M
rate quotes served every day, without breaking a sweat.
<40ms
freight-quote latency at p99, end to end.
0
double-refunds in two years of an idempotent pipeline.
01
Selected work
Systems I have shipped
freight-rating02 / 04
Real-time freight rating
Quote service for full-truckload and LTL freight. Rebuilt the pricing path so a quote returns in under 40ms at p99, at 8M requests a day.
refund-engine03 / 04
Idempotent refund pipeline
Refunds modelled as an explicit state machine with idempotency keys and partial-failure handling, so finance reconciles every cent. Zero double-refunds in two years.
pg-outbox04 / 04
Transactional outbox
The outbox pattern as a tiny crate — exactly-once-ish event delivery from a single Postgres table. Given away.
02
Experience — Twelve years in logistics
2022 — nowCurrently
Principal Backend Engineer
Routing & pricing platform · Rust · Go
- Designed the routing engine that scores 40+ carriers on cost, SLA, and live capacity for every shipment.
- Led the Python → Rust migration of the hot path, cutting p99 latency 11×.
- Own the rating service serving 8M quotes a day at p99 < 40ms.
11×faster p99
8Mquotes / day
60%fewer mis-routes
Carrier routing engine
2018 — 2022
Senior Backend Engineer
Parcel logistics SaaS · Python · Rust
- Built the integration layer normalizing 40+ courier APIs behind one internal contract.
- Designed the transactional outbox that kept order state exactly-once across every carrier.
- Tamed flaky third-party APIs with retries, backoff, and circuit breakers.
40+courier APIs
1internal contract
exactlyonce delivery
Integration layer & transactional outbox
2014 — 2018
Backend Engineer
First parcel platform · Python · Django
- Shipped the original tracking and refund services from zero on Django.
- Modelled refunds as an explicit state machine with idempotency keys.
- Learned the hard way why refunds are not negative payments.
0double-refunds
2services from zero
4 yrsin production
Idempotent refund state machine
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.
hi@czeresniowski.devBased in Grenaa, Denmark · remoteReplies within a dayAvailable now
GitHub ↗LinkedIn — soon