Jonas Mattes
From idea to product for Cambridge teams.
I'm a senior full-stack TypeScript engineer who helps Cambridge startups, small businesses, and research teams turn an idea, a stalled prototype, or a manual process into shippable, production software — 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.
In their words
“Jonas has been with Kipti from the start and built the product with us. He doesn't just think in tasks — he thinks in the product and the company, and brings as much strategically as he does technically.”
Jonas begleitet Kipti seit dem Anfang und hat das Produkt gemeinsam mit uns aufgebaut. Er denkt nicht nur in Tasks, sondern im Produkt und im Unternehmen mit – und bringt strategisch genauso viel ein wie technisch.
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
I start with a short paid discovery — usually 2–5 days — so we agree on what we're building, name the riskiest unknowns, and I can give you a fixed price for the build phase.
Thin vertical slice
I ship a narrow end-to-end slice in the first weeks. It de-risks the data model and the integration shape before we add surface area.
Iterate in production
I deploy continuously to a real user from week three, so your feedback shapes the build instead of arriving in a post-mortem.
Handover
I stay on a light retainer for the weeks after launch to handle bugs and the first iteration, then hand over full documentation for whoever picks it up next.
Engagement & rates
Ongoing engagements from £500/day.
In-team engagements are billed at £500–650/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 teams 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 startups, small businesses, and university research teams. My freelance proof is European (the named case study below is a German edtech), and my home base is Cambridge — close to Silicon Fen's founders and research labs, 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 startups?
- No. Early-stage MVPs are a sweet spot, but small businesses digitising a manual process and research teams needing a bespoke tool hire me just as often. 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 clients 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.