Hybrid Senior Backend Engineer – API Trading

at Flowdesk

• Job title: Senior Backend Engineer – API Trading
• Job type: Full Time
• Experience level: Senior
• Salary: Not specified
• Degree requirement: Bachelor's Degree
• Tech skills: Open Source, Rust, TypeScript
• Location requirements: Hybrid, Paris, France

About the role

• Senior Software Engineer designing, building, and scaling trading APIs for financial institution. Collaborating across teams to ensure low-latency, high-quality API performance.

Responsibilities

• **Design and build competitive trading APIs**
• Architect and implement public trading APIs (REST, WebSocket, and FIX) in Rust.
• Ensure low-latency, high-throughput access to trading workflows (orders, balances, positions, executions).
• **Own the API lifecycle end-to-end**
• Define and maintain OpenAPI specifications and other interface contracts.
• Keep APIs consistent, versioned, and easy to integrate for external clients.
• Drive clear, accurate, and up-to-date API documentation that external developers actually want to read.
• **Build secure, robust authentication flows**
• Design and implement authentication and authorization for public trading APIs.
• Apply best practices around key management, signatures, rate limiting, replay protection, and abuse prevention.
• **Collaborate across trading, product, and engineering**
• Work closely with internal stakeholders (including Jing and Tony) to understand trading needs and constraints.
• Translate trading and product requirements into clean API designs and reliable backend flows.
• Partner with frontend / tooling teams (TypeScript) to ensure smooth end-to-end integration.
• **Raise the bar on reliability and quality**
• Ensure APIs are observable, well-tested, and resilient under peak load.
• Contribute to standards, patterns, and tooling for API development across the team.
• Help review code, mentor teammates, and share best practices in Rust, security, and API design.

Requirements

• **Must Have**
• English is mandatory
• 5+ years of backend software engineering experience, ideally in trading, crypto, or high-throughput financial systems.
• Proven track record designing and shipping client-facing APIs used in production.
• Hands-on experience building and operating backend services in Rust.
• Comfortable owning services in production - performance, observability, debugging.
• Direct experience building or maintaining a public API for an exchange or trading firm (or very similar environment).
• Strong knowledge of REST and WebSocket APIs (protocol design, error handling, rate limits, versioning).
• Experience with OpenAPI (specs, code generation, compatibility management).
• FIX protocol knowledge is a big plus.
• Solid experience implementing API authentication (HMAC / key-based auth, signatures, tokens).
• Understanding of common API attack vectors and mitigations (OWASP-style threats, replay attacks, abuse control).
• Comfortable working with TypeScript for SDKs, tooling, or integration layers.
• Able to think from the integrator’s perspective - how developers discover, test, and use your APIs.
• Clear, concise communicator in English (written and spoken).
• Able to work closely with trading, product, and other engineering teams, challenge requirements when needed, and converge on practical solutions.
• Nice to Have
• Experience in crypto trading, digital asset exchanges, or market making.
• Exposure to matching engines, execution engines, or algorithmic trading systems (designing APIs around them is a strong plus).
• Strong interest or background in security (secure coding practices, threat modeling, cryptographic primitives).
• Contributions to open source around APIs, Rust, or security.

Benefits

• > International environment (English is the main language)
• > 50% of transportation costs & a sustainable mobility agreement
• > Swile lunch voucher (€9.25 per day, 60% covered)
• > 100% Alan Blue covered for you and your children
• > Wellpass contribution to gym membership
• > Team events and offsites