Flowdesk

Senior Backend Engineer – API Trading

Flowdesk

full-time

Posted on:

Location Type: Hybrid

Location: Paris • France

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Job Level

Senior

Tech Stack

Open SourceRustTypeScript

About the role

  • **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
Applicant Tracking System Keywords

Tip: use these terms in your resume and cover letter to boost ATS matches.

Hard Skills & Tools
RustAPI designRESTWebSocketOpenAPIFIX protocolAPI authenticationHMACkey-based authenticationdebugging
Soft Skills
clear communicationcollaborationproblem-solvingmentoringconcise writingadaptabilitycritical thinkingstakeholder engagementteamworkuser perspective