Part 2Tech LabFull-Stack Product EngineerOwn a product end to end — the users, the roadmap, the build and the release — with nobody standing between you and the people who use it.BarcelonaOpen5 seatsWhat you own01 The users, in person02 What gets built next, and why03 The build, front to back04 Whether it gets usedOne method, many productsMainloop is an engineering company in Barcelona.
We own what we build and we answer to ourselves.
You get the interesting part of a new company, with a real customer and real products from day one.What we build is the software that automates professional-services work — across roughly fifteen countries, for businesses that are drowning in process.
We work in two halves.
One half goes into a business, works out what actually happens there, and proves fast whether an idea is worth having.The other half — this half — takes what is proven and owns it for years.This is the seat where the product and the engineering are the same job.Most of our products are run by a pair: a Product Owner who holds the business, and an engineer who holds the build.
Some of them do not need two people.
They are smaller, their users sit close enough to talk to directly, and a separate PO would be a relay rather than a help.
Those products are run by one person, and that person is you.What the job actually isYou own a product end to end.
Not a slice of it, and not the tickets someone else wrote about it.You decide what it should do next, you build it, you ship it, and you find out whether it worked.You talk to the people who use it.
In person when you can.
You read the feedback, you watch how the product is really used, and you notice the workaround nobody thought to mention — because the workaround is usually the next feature.You decide what comes next.




There is no one above you writing the roadmap for your product and no one below you writing the stories.
You choose what moves the outcome, what waits, and what you decline — with a reason the person asking can respect.You build it, front to back.
The interface, the logic underneath, the data it keeps.
You decide whether a feature makes sense on the screen and whether it holds up behind it, which is exactly the judgement that gets lost when those two calls belong to different people.You ship it and you measure it.
A feature is not done when it merges; it is done when people use it and the number moves.
You own that number — time saved, errors avoided, uptake — and you report it whether it flatters us or not.You carry more than one.
Our products are built on the same scaffold and arrive the same shape, so one person can own several small ones well.
New ones keep arriving from the other half of the team.How this differs from the Full-Stack Engineer seatBoth seats sit in the Tech Lab, both build with agents, and both own products for years.
The difference is where the product decisions live.A Full-Stack Engineer works beside a Product Owner, who holds the business relationship and the roadmap, and owns the build, the architecture and the release.A Full-Stack Product Engineer holds both halves— on products small enough, and close enough to their users,



that splitting them would only slow the product down.If you want to go deep on architecture and let someone else hold the room, the Full-Stack Engineer ad is the better fit.
If you care as much about whether a feature should exist as about how to build it, this one is.You will get seriously good at building with AI agentsWe are an AI-native team, genuinely — not a team that added a Copilot licence.Every engineer gets their own Claude Max subscription and a desktop orchestrator that runs several coding agents in parallel.
In this seat that changes the arithmetic of the job: when building is fast, the expensive part is deciding — and you are the person who does both.Every change is reviewed by an agent before a person signs it off.Every build ships tests, and the gate is 100% pass.
Unit, smoke against the real running thing, and browser-level end-to-end.Anything AI-powered ships with evals — a scored set of inputs, not "it looked right when I tried it".
If agents write the code, what am I for?
The Agents Will Build Anything, Quickly And Confidently — Including The Wrong Thing.
In This Seat The Risk Is Not Slow Software, It Is Fast Software Nobody Needed.
What Stays Yours, PermanentlyFinding out what people actually need.
Users describe what they ask for, not what would help.
Reading the difference takes a person who has watched them work.Deciding what not to build.
Somebody has to be the person for whom "no" is a complete sentence with a reason attached.Turning a need into a specification that is actually right.
An agent builds exactly what you specify, beautifully, even when what you specified was the wrong shape.Judging the output.
Agent code compile

📌 Full-Stack Product Engineer (España)
🏢 Mainloop AI
📍 España