Senior Rust Software Engineer in London

About Onyx Capital Group

Onyx Capital Group is the world’s #1 liquidity provider for energy derivatives, trading over $3.2 trillion in notional value annually. Through Onyx Commodities, the Flux Terminal, and our trading division Axis, we dominate the benchmarks that matter — Dated Brent, S2F contracts, and beyond. We are a technology‑driven market‑making powerhouse at the intersection of global energy markets, data, and engineering — and we are growing fast.

Engineering at Onyx

We don’t hire passengers — we hire pilots. Every engineer here takes ownership, pushes back when the design isn’t right, and holds the bar high without being asked. We practise TDD, design for observability from day one, and treat software craftsmanship as a genuine competitive advantage. The team is small, senior, and embedded directly in the trading floor. There are no layers of abstraction between you and the business — your work has immediate, measurable impact from day one.

The Opportunity

We are building our Sri Lanka engineering hub and looking for Senior Rust Software Engineers to be founding members of that team. Working alongside our global engineering organisation, you will take full ownership of complex systems end-to-end — from architecture and design through delivery and into production. Your work will power live trading infrastructure used by some of the world’s most demanding market participants.

• 5–10+ years in a software engineering role; track record of delivering production‑quality features independently
• Deep Rust expertise — ownership, lifetimes, trait objects, unsafe code, async runtimes, and macro authorship; comfortable working at the boundary of safe and systems‑level Rust in production
• Demonstrated experience building low‑latency, high‑throughput systems in Rust — including performance profiling, benchmarking, and architectural ownership of critical‑path services
• Strong systems programming fundamentals — memory layout, concurrency primitives, and lock‑free data structures applied in real‑world, performance‑critical environments
• Test‑Driven Development discipline: unit, integration, and E2E tests written as a standard part of the development loop, not an afterthought
• Automation mindset — demonstrated experience identifying and eliminating manual processes through tooling, scripts, and pipelines
• REST API experience — designing, building, and consuming APIs with a clear understanding of authentication, versioning, and error handling
• Source control and CI/CD: GitHub, Azure DevOps, or GitLab; branching strategies, PR workflows, and pipeline contribution
• Experience working in cloud‑hosted environments — Azure preferred
• Strong sense of personal ownership — takes a feature from ticket to production without hand‑holding, and treats issues in systems they’ve built as their own to resolve
• Comfortable engaging directly with remote end users and business stakeholders to understand requirements, debug issues, and communicate progress clearly — without needing a middleman
• Highly self‑motivated with a bias for action — raises problems early, proposes solutions, and follows through to completion
• Strong written and spoken English — clear and confident in both written and verbal communication across synchronous and asynchronous settings
• Experience working with globally distributed teams is strongly welcomed; comfortable collaborating with colleagues in different time zones and cultures

Nice to Have

• FFI experience — calling into C/C++ libraries from Rust or exposing Rust APIs to other languages
• Experience with async Rust runtimes (Tokio / async‑std) and designing concurrent, fault‑tolerant service architectures
• Experience with agile delivery practices (sprint planning, retrospectives, stand‑ups)
• Prior experience in financial services or fintech, or a genuine interest in financial technology and capital markets — not required, but candidates who are curious about the domain tend to thrive here
• Familiarity with message‑based architectures (Kafka, NATS, etc.), gRPC / protobuf, or low‑level networking (TCP/UDP, DPDK)
• Experience mentoring engineers, leading technical design reviews, or establishing Rust best practices and toolchain standards within a team

What We’re Looking For

You write clean, well‑tested code and take pride in it. You don’t wait to be told what needs improving — you spot it, raise it, and fix it. You communicate proactively, work autonomously across time zones, and hold yourself to a standard that makes the people around you better. You want to work on systems that matter and with users who notice when something is even slightly wrong.