First or lead engineer
Take a product from idea to production, and set up the architecture, tooling and team habits it will live with for years.
Marc Römmelt
Senior software engineer. Usually the first or lead engineer on a product: I set up the architecture, keep it boring, and stay long enough to defend it.
ask
Questions? Ask the genie.
It knows my work, my terms and my limits, and it passes real enquiries straight to me.
An AI assistant answers from what Marc wrote about himself and passes enquiries on to Marc. Datenschutz
what I do
Hard backend problems, solved simply.
Untangling systems
Multi-tenancy, service boundaries, independent deploys, migrations off frameworks that stopped fitting. Backwards-compatible, while production keeps running.
Event-driven backends
Queues, idempotent consumers, event sourcing and CQRS where correctness matters, like payroll that must reproduce any past month exactly.
AI that does real work
Real-time voice agents, LLM tool calling and WhatsApp integrations, with DSGVO and EU data residency designed in.
selected work
Six projects since 2019.
Self-taught, with a degree in entrepreneurship and a founder's habit of owning the whole product. Each project opens into the context, the decisions and the stack.
- 2026 — nowSparkassen-FinanzgruppeSenior engineer, freelance · via Web Computing GmbHDecoupling about 20 services behind a chatbot with 300+ tenants, so each service ships on its own while the platform stays in production.
- 2026CalluraFounder and sole engineer · own productPhone and WhatsApp AI for funeral homes. Built end to end on infrastructure that cost about as much as dinner per month. Now paused.
- 2023 — 2026PenzillaLead engineer · B2B SaaS for corporate pensionsSecond engineer, then tech lead; grew the team from two to six. Rebuilt multi-tenancy (query timeouts to zero, database connections from 200 to 20) and built event-sourced payroll integrated with DATEV, SAP and Personio.
- 2022 — 2023TheMakers.aiTechnical lead · B2B marketplaceTurned a proof of concept into a maintainable product. Hired and led four engineers and a product manager.
- 2021 — 2022FanzoneLead engineer, freelance · sports collectiblesOne codebase for web, iOS and Android. Introduced test-driven development through mob programming.
- 2019 — 2020ELIGOEngineer · candidate assessmentBroke up a monolithic Vue.js front end and built multi-tenant theming and authentication.
how I build
Complexity very, very bad.
My LinkedIn headline, borrowed from The Grug Brained Developer by Carson Gross. It is a joke. It is also the method.
Boring first
Postgres, a monolith, one server, until the problem proves it needs more. Distribution is a cost; pay it where it earns its keep.
Measure, then fix
Traces and a baseline before anyone says "fixed".
Plain over clever
Pure functions, honest types, code a new teammate can follow on day one.
Tests first
Test-driven by default. It is how I move fast without breaking what pays the bills.
Privacy from the first diagram
DSGVO, EU hosting and the AI Act shape the design before the first line of code.
Agents as power tools
Claude Code drafts, I review until I own every line. Faster, same standard. Where the client agrees, of course.
stack
Tools I reach for.
working together
Freelance, remote-first, in for the long run.
- Contract
- Through 0815 Software UG, billed hourly. Direct or through an agency.
- Location
- Remote-first. On-site around Nürnberg whenever it helps, elsewhere for kick-offs.
- Duration
- Three months or longer. Short architecture reviews too.
- Availability
- On request. I finish engagements properly before starting the next.
contact
Got a hard problem? Tell me about it.
I read and answer every message myself.
- call
- Book a call
- hallo@marcroemmelt.de
- in/marcroemmelt
- cv
- Marc_Roemmelt_CV.pdf