> Markdown version of [/jobs/ext/1691182-lead-full-stack-engineer](https://www.wearedevelopers.com/jobs/ext/1691182-lead-full-stack-engineer). Every page supports `.md` or `Accept: text/markdown`. Links point to the HTML versions so they work for humans too. Agent guide: [/agents.md](https://www.wearedevelopers.com/agents.md). --- # Lead Full-Stack Engineer - **Company:** Complexio - **Location:** Madrid, Spain - **Contract:** Permanent contract - **Skills:** Artificial Intelligence, Architectural Patterns, Graph Database, Software Product Management, Software Architecture, WebSocket, Backend, Low Latency, Front End Software Development, Restful APIs - **Published:** July 23, 2026 - **Apply:** https://www.buscojobs.com.es/lead-full-stack-engineer-en-madrid-ID-364481957 ## About the Role 5+ years of frontend experience in production. You understand rendering models, performance characteristics, and architectural patterns deeply. Strong product sense. You push back when the UX doesn't make sense. You've shipped real user-facing products. Real-time/streaming UI experience. WebSockets, SSE, or similar live data patterns. Comfort with ambiguity. You take vague problems and turn them into concrete frontend solutions. You ship. End-to-end - prototype to production to iteration on feedback. Strong signals Enterprise/B2B SaaS. You know the difference between consumer UX and building for a CFO who needs to trust a number. AI product experience. Latency UX, citation rendering, hallucination presentation. Design sensibility. Polished interfaces without a designer in the room. Backend literacy. You can read a REST API and collaborate with backend engineers on data contracts. Startup experience. Small teams, multiple hats, fast without cutting corners. How We Work Direct communication. Honest feedback, hard questions, no hiding behind process. Ownership over tasks. You're asked what you shipped and learned, not to fill out status reports. Speed with quality. ## Description Complexio is building Stevie - an enterprise AI knowledge assistant that gives executives and operators a complete view of their organization through knowledge graphs.Our customers are large maritime shipping companies managing hundreds of vessels, thousands of daily emails, and complex commercial operations.We're looking for a Senior or Lead Frontend Engineer to own Stevie's frontend.The interface is the product - it determines whether enterprise customers trust the intelligence, get value quickly, and come back.You'll shape all of that.Why This Role¡Inscríbase sin demora!Se espera un gran volumen de solicitantes para el puesto que se detalla a continuación, no espere para enviar su CV.Enterprise AI UX is unsolved.You won't copy patterns - you'll create them.Citations from knowledge graphs, streaming AI responses that feel trustworthy, confidence indicators on operational intelligence.You own the full frontend.No separate frontend team.You are it - with real influence on product direction and architectural decisions.Flat org, real impact.Domain owners have authority.Engineering decisions are made by engineers, not managers.You'll own the full frontend - conversational AI interfaces, content feeds, document generation, collaborative features.The product is evolving fast and you'll shape what gets built and how.Must-haves5+ years of frontend experience in production.You understand rendering models, performance characteristics, and architectural patterns deeply.Strong product sense.You push back when the UX doesn't make sense.You've shipped real user-facing products.Real-time/streaming UI experience.WebSockets, SSE, or similar live data patterns.Comfort with ambiguity.You take vague problems and turn them into concrete frontend solutions.You ship.End-to-end - prototype to production to iteration on feedback.Strong signalsEnterprise/B2B SaaS.You know the difference between consumer UX and building for a CFO who needs to trust a number.AI product experience.Latency UX, citation rendering, hallucination presentation.Design sensibility.Polished interfaces without a designer in the room.Backend literacy.You can read a REST API and collaborate with backend engineers on data contracts.Startup experience.Small teams, multiple hats, fast without cutting corners.How We WorkDirect communication.Honest feedback, hard questions, no hiding behind process.Ownership over tasks.You're asked what you shipped and learned, not to fill out status reports.Speed with quality.We ship fast because we scope well.Customer feedback cycles are weeks, not quarters.AI-augmented workflow.xcskxlj We use AI tools extensively and expect you to be comfortable with AI-assisted development.#J-*****-Ljbffr ## Related Videos - [But, you're not Facebook](https://www.wearedevelopers.com/videos/378-but-you-re-not-facebook) - [Developing the Backend with Stefan Lingler, CTO at Shpock](https://www.wearedevelopers.com/videos/100360-developing-the-backend-with-stefan-lingler-cto-at-shpock) - [Minimal infrastructure for Real‑Time Phone Agents: transcripts in, responses out](https://www.wearedevelopers.com/videos/1736-minimal-infrastructure-for-real-time-phone-agents-transcripts-in-responses-out) - [Swapping Low Latency Data Storage Under High Load](https://www.wearedevelopers.com/videos/746-swapping-low-latency-data-storage-under-high-load) - [Meet Your New BFF: Backend to Frontend without the Duct Tape](https://www.wearedevelopers.com/videos/682-meet-your-new-bff-backend-to-frontend-without-the-duct-tape) - [Nest.js - TypeScript in the backend can also be clean](https://www.wearedevelopers.com/videos/1033-nest-js-typescript-in-the-backend-can-also-be-clean) ## Related Articles - [How We Built a Worry-Free System That Runs for 10+ Years – And What We’d Do Again](https://www.wearedevelopers.com/magazine/751-how-we-built-a-worry-free-system-that-runs-for-10-years-and-what-we-d-do-again) - [Dev Digest 120 - Apple and peers](https://www.wearedevelopers.com/magazine/455-dev-digest-120-apple-and-peers) - [Navigating the AI Shift](https://www.wearedevelopers.com/magazine/629-navigating-the-ai-shift) - [Never delegate the understanding](https://www.wearedevelopers.com/magazine/749-never-delegate-the-understanding) - [Dev Digest 121 - AI goes offline](https://www.wearedevelopers.com/magazine/456-dev-digest-121-ai-goes-offline) - [Dev Digest 132 - Binging WADFlix?](https://www.wearedevelopers.com/magazine/473-dev-digest-132-binging-wadflix)