# Senior Fullstack Engineer (TypeScript) > Cryptonext Security · Paris, France (Hybrid) · Full-time · Posted 2026-08-10 **Workplace:** hybrid **Department:** Research & Development ## Description ### Who we are CryptoNext Security is a deeptech startup specializing in post-quantum cryptography. Our solutions help businesses and institutions prepare for a future where quantum computers will challenge traditional data security. We work with leading clients in finance, defense, and telecommunications. ### On a daily basis, you will •     Own features end to end in TypeScript: Hono and Node.js on PostgreSQL, React SPA on the front. •     Design HTTP APIs consumed through Hono's typed RPC client, with generated OpenAPI specs. •     Model and query PostgreSQL: schema, migrations, query performance. •     Build interfaces with Vite, TanStack, Tailwind and shadcn/ui. •     Work directly with Product and QA. •     Write the unit and integration tests that back your features, and give QA what they need to automate the rest. •     Review code. •     Use AI coding tools as leverage under your own judgement, staying accountable for what lands in the repo. •     Propose upgrades and refactorings, and explain the trade-offs you accepted. ### How we work A team of six engineers, within our 15-person R&D department. A single TypeScript monorepo, with shared types and tooling across services and front. Three days a week in our Paris office, the rest remote. Short feedback loops, high standards. We ship a working version early rather than polishing in isolation, and keep solutions as simple as the problem allows. Our products ship on-premise, sometimes into air-gapped environments, so builds have to be reproducible and dependencies deliberate. We build software our clients rely on for security: secure defaults, reviewed dependencies and tested code are part of shipping, not a later phase. We care more about a decision you can justify than a pattern you can name. ## Requirements ### The skills you'll need •     Strong TypeScript across the stack: strict mode, generics, types shared between server and client instead of duplicated. •     Node.js backend: API design, auth, error handling, observability. •     Asynchronous processing: queue consumers and background workers, idempotency, retries and failure handling, backpressure. •     PostgreSQL: schema design, migrations and rollbacks, indexing, reading a query plan. •     Strong React: hooks, composition, clear state boundaries, client-side routing and server state caching. •     Comfortable with a modern frontend toolchain: fast bundling, utility-first styling, component libraries you extend rather than fight. •     API contract design: REST, OpenAPI, typed clients, versioning. •     Unit and integration testing, with a defensible position on what belongs at which level and on what is worth testing at all. •     Real use of AI-assisted development in a production codebase: agentic workflows, context management, reviewing generated output as critically as a colleague's merge request. You have a view on where these tools pay off and where they create debt. •     Seniority means you can say why you chose an approach, what you rejected, and what it will cost in six months. ### Bonus skills •     Go, used in parts of our codebase. •     Hono typed RPC and end-to-end type inference. •     Secure coding practices and application security. •     Basic understanding of cryptography and cybersecurity. •     Experience in a startup or deeptech environment. ## Benefits ### The team you'll be joining You will join a team of six engineers who own their features across the whole stack, inside our 15-person R&D department, working closely with Product and QA. You will report to the Head of Engineering and collaborate with other departments to build the backend services and interfaces our clients depend on. ### Our recruitment process 1.   **Initial discussion** with our HR team to explore your background and motivations. 2.   **Technical interview** with a developer: a live coding session of 1 to 1.5 hours. AI coding tools are required, not merely allowed. We are interested in how you direct and review them. No take-home assignment. 3.   **Meeting with a manager** to ensure alignment with our company culture. 4.   If successful, you'll receive a final offer! ### What's in it for you at CryptoNext •     A stimulating work environment with cutting-edge technological challenges. •     A competitive salary, aligned with our compensation philosophy. •     A deep dive into the exciting world of post-quantum cryptography and cybersecurity. Ready to join the adventure? **Apply now!** ## Apply [Apply at Cryptonext Security](https://apply.workable.com/cryptonext-security/j/C7BE4A5E87/apply) --- Powered by [Workable](https://www.workable.com)