Middle Full Stack Developer (Node.js/React)

About the team:

We are a passionate and ambitious team of 120+ people building pdfFiller, an online platform for creating, editing, and signing PDF documents.

pdfFiller empowers over 10 million users every month to create and edit PDFs, send them for signing, and securely store documents within a single application. Offering unlimited storage, unlimited templates, and cross-platform integration, pdfFiller is the only PDF editor needed to get your document done.

And now, we are looking for a Full Stack Developer who is prepared to contribute to the next chapter of our company's growth.

The team builds an AI assistant that understands users' documents and acts on them, an MCP server that exposes pdfFiller's capabilities to external AI clients, and AI-powered improvements to existing product features. Our engineers propose improvements rather than just execute tickets, and our roadmap is planned a year ahead but stays flexible. You'll also get an educational budget, regular knowledge-sharing sessions, and a clear growth path.

As Full Stack Developer, you will build tool-calling, streaming, and RAG features that real users rely on, owning them from problem definition to production metrics, with a focus that is about 80% backend and 20% frontend.

What you'll be working on:

• standards, and acceptance criteria
• Own features end to end, from requirements to production and post-release monitoring of edge cases
• Own the automated quality of what you ship, including unit and integration tests and eval cases for LLM behavior
• Treat prompt regressions, evals, and non-determinism as everyday engineering concerns
• Review code and documentation to keep the codebase consistent
• Take part in the duty rotation: monitor production and respond to incidents
• Propose improvements to processes, tooling, and legacy code as part of the team's ongoing modernization
• Work with our stack: Node.js, TypeScript, NestJS, LangGraph, Vercel AI SDK, PostgreSQL + pgvector, Drizzle ORM, Valkey, LiteLLM, Langfuse, OpenTelemetry, Zod, and Jest on the backend; React, TypeScript, Webpack 5 + Module Federation, yarn workspaces + Lerna, React Testing Library, and Playwright on the frontend; Docker, GitHub Actions, ECR, ArgoCD, the Grafana stack, and AWS S3 for infrastructure

What we expect from you:

• Experience with LangGraph or LangChain, agent orchestration, and state machines
• Experience with RAG and vector search (pgvector)
• Familiarity with SSE or other streaming protocols
• Experience with observability tools such as OpenTelemetry and the Grafana stack
• Experience with LLM evaluation, including eval datasets and LLM-as-judge
• Experience writing technical documentation (C4, ADR)

What helps you rock:

• Experience with LangGraph or LangChain, agent orchestration, and state machines
• Experience with RAG and vector search (pgvector)
• Experience with SSE or other streaming protocols
• Experience with observability tools: OpenTelemetry, the Grafana stack
• Experience with LLM evaluation: eval datasets, LLM-as-judge
• Experience writing tech documentation (C4 model, ADRs)