Senior Fullstack Engineer

This is a remote role based in Romania only.

At AiSentr, we're building a platform that simplifies the implementation of AI into business workflows for businesses that lack in-house data science or engineering capabilities. Our product combines data ingestion, multi-layered search, and LLM-driven learning to offer customers workflow automation that can converse with and learn from their internal knowledge, through a user-friendly, self-managed interface. 

We're a small team that hires people who can own problems end to end, who default to simplicity and who love to build great products for enthusiastic customers.

The Role

We're looking for a Senior Fullstack Engineer to work across our entire product surface - frontend, backend, and the AI orchestration layer that connects them. You won't be pigeonholed. Some weeks you'll be deep in React building complex UI for our workflow editor. Other weeks you'll be writing backend services, designing API contracts, or wiring up new agent capabilities. The work goes where it needs to go, and so will you.

You'll report to our CTO and collaborate closely with Product and Design. We have a high volume of workflow nodes to design and build - discrete, well-scoped units of work that demand efficient, thoughtful engineering rather than heroic complexity.

What You'll Do

Build across the stack

• Develop and ship features end-to-end: from responsive, performant UI in React and Next.js, through REST APIs in NestJS, to data persistence in Postgres and MSSQL.
• Implement real-time experiences using SSE for streaming LLM responses to users.
• Design and build workflow nodes - the core building blocks of our automation platform - with clean interfaces and predictable behaviour.
• Work directly within our AI agent orchestration layer (Mastra), defining tools, composing agents, and shaping how our product reasons and acts on behalf of users.

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Shape the product's technical direction

• Evaluate architectural trade-offs pragmatically: we want the simplest thing that works well, not the most impressive thing that works sometimes.
• Contribute to frontend architecture decisions - component libraries, state management, data-fetching strategies - while holding the same standard on the backend.
• Define clear API contracts between frontend and backend services, ensuring consistency and reliability as the platform grows.

Work like an owner

• Deploy your own work. Our CI/CD runs through GitHub Actions and our infrastructure is straightforward - you'll be shipping independently within your first week.
• Identify gaps, propose solutions, and execute without waiting for permission. We don't have layers of process. If something needs doing, do it.
• Write code that your future self (and your teammates) will thank you for. We value clarity, tests, and documentation over cleverness.

What We're Looking For

• 5+ years of commercial experience building and shipping web applications across frontend and backend.
• Strong proficiency in TypeScript - not just framework-level usage, but genuine understanding of the language and its type system.
• Deep experience with React: you understand rendering behaviour, hooks, performance optimisation, and component composition - not just how to make things appear on screen.
• Solid backend experience with Node.js. Experience with NestJS is a plus, but strong fundamentals matter more than framework familiarity.
• Comfort working with relational databases (Postgres, SQL Server) - writing queries, designing schemas, thinking about data access patterns.

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• The ability to pick things up fast. Our stack spans frontend, backend, AI orchestration, and cloud infrastructure. You don't need to know all of it on day one, but you need to be the kind of person who figures things out independently.
• A bias toward simplicity. If your instinct is to reach for a microservice when a function will do, or to introduce a state management library when local state is fine, we're probably not the right fit.

What Will Set You Apart

• Experience with AI agent frameworks or orchestration tools (Mastra, LangChain, CrewAI, or similar). If you've built, composed, or debugged agentic workflows, you'll hit the ground running.
• Familiarity with Azure services - particularly AKS, Blob Storage, or AI Search.
• Experience with SSE or WebSocket implementations for real-time streaming interfaces.
• A track record of working in early-stage or small-team environments where you wore multiple hats and thrived.
• Experience building workflow or node-based editors, automation tools, or integration platforms.

What We Offer

• A competitive, long term B2B contract (or FTE if preferred)
• Fully remote, Romania-based.
• A small, senior team where your work has direct, visible impact on the product and the business.
• No process for the sake of process.
• Genuine technical variety - you'll work across the full stack and into the AI layer, not sit in one corner of the codebase.
• A working environment that cares about its team, our customers and above all our product.