Jonas Mattes
AI-powered product builds for Cambridge startups.
I'm a senior full-stack TypeScript engineer who helps Cambridge startups and scale-ups take early-stage ideas and stalled prototypes to shippable, production products — with an AI layer when it earns its place.
Worked with
Previously — as an employee or via consulting engagements. Distinct from the named freelance client featured below.
- GoogleEmployer
- ZühlkeEmployer
- BMWEmployer
- AudiEmployer
- SBBIndirect
Services
Three ways to work together.
MVP build
6–16 weeks
Take an idea or stalled prototype to a shippable product. End-to-end design, build, and launch.
AI feature integration
2–6 weeks
Add a polished LLM layer to an existing product — chat UIs, summarisation, pattern detection. No bolted-on API calls.
In-team senior engineer
3–5 days/week · £500–650/day
Join an existing team 3–5 days a week to ship alongside your engineers as a senior technical contributor.
Process
How an engagement actually works.
Every project is individual, so the shape of the work shifts to fit it — but an engagement often looks like this.
Discovery
A short paid discovery — usually 2–5 days — to align on what we're building, the riskiest unknowns, and a fixed price for the build phase.
Thin vertical slice
Ship a narrow end-to-end slice in the first weeks. De-risks the data model and integration shape before adding surface area.
Iterate in production
Continuous deploys to a real user from week three. Feedback shapes the build instead of waiting for a post-mortem.
Handover
Light retainer for the weeks after launch to handle bugs and the first iteration, then full documentation for the next team.
Engagement & rates
Ongoing engagements from £550/day.
In-team engagements are billed at £550–650/day. MVP and AI integration projects are scoped per engagement after a short paid discovery.
Fixed-scope project
Defined deliverable, fixed timeline, scoped per engagement. Best for MVPs and AI feature integrations.
Ongoing retainer / fractional
Reserved capacity for an existing team or product. Best for in-team engagements and post-launch evolution.
About
Cambridge-based, shipping for startups across the UK and Europe.
I'm Jonas — a senior full-stack TypeScript engineer with a decade in engineering, now freelancing with early-stage teams to take product ideas from zero to production. I was previously a software engineer at Google and shipped products at Zühlke for clients including SBB.
Today I work as a freelance AI-product engineer with Cambridge tech startups and university spinouts. My freelance proof is European (the named case study below is a German edtech), and my home base is Cambridge — close to Silicon Fen founders and an easy day-trip from London.
Read my full background →FAQ
Common questions.
- Are you available right now?
- I take on a small number of engagements at a time. The fastest way to find out is to send an enquiry with your timeline.
- Do you only work with early-stage startups?
- No — early-stage MVPs are a sweet spot, but scale-ups hire me too. For a growing team I'll usually embed 3–5 days a week as a senior engineer, ship a discrete product or AI feature, or help get a stalled build back on track.
- Do you work on-site or remote?
- I'm Cambridge-based and ship for startups across the UK and Europe. On-site days in Cambridge or London are easy; full remote works for most engagements.
- How do you scope a project?
- I start with a short paid discovery — usually a week — to align on what we're building, the risks, and a fixed price for the build phase.
- What happens after handover?
- Most clients keep me on a light retainer for a few weeks post-launch to handle bugs and the inevitable first iteration. After that, I document everything for the next team.
- Do you sign an NDA?
- Yes — happy to sign yours, or use a short mutual NDA before sharing anything sensitive.
Get in touch
Tell me what you're building.
A short note about your project, timeline, and budget helps me reply usefully.