Senior Fullstack Engineer (TypeScript)

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. …