Markus Dethlefsen — Senior Fullstack Developer

— selected work —

Trade Journal

A personal trading journal that treats record-keeping as a product: orders, trades, capital and performance analytics, open as a live demo. Built to stay maintainable — strict service-layer separation and a five-layer test setup from unit to dockerized smoke and e2e.

Next.js 15 · React 19 · TypeScript · Drizzle · libSQL · Playwright

> live demo

Mampf

A shared shopping list for a two-person household: type a dish, get its ingredients — resolved by an LLM against each person's diet profile and live-synced between devices. The public demo drops you into a sandboxed household that resets on every visit.

SvelteKit · Svelte 5 · TypeScript · SQLite · SSE · OpenRouter

> live demo > source on request

server.registerTool(
  "search_messages",
  {
    description:
      "Search a mailbox by from/subject/body/since.",
    inputSchema: {
      account: z.string().optional(),
      mailbox: z.string().default("INBOX"),
      from: z.string().optional(),
      subject: z.string().optional(),
      body: z.string().optional(),
      since: z.string().datetime().optional(),
      limit: z.number().int().min(1).max(200)
        .default(20),
    },
  },
  async ({ account, ...opts }) =>
    json(await searchMessages(
      resolveAccount(accounts, account), opts)),
);

email-mcp

A Model Context Protocol server that gives an AI assistant a real mail workflow: IMAP, local full-text search via notmuch, rule-based classification, draft lifecycle tracking, audit logging. Around 20 tools and 5,000 lines of TypeScript — running my own mail every day.

TypeScript · Express · Zod · imapflow · notmuch

> source on request

— track record —

2025 – now

Independent product work Own products & AI-assisted workflows

Self-directed development phase: shipping my own products end to end — trade journal, MCP servers in TypeScript and Python, Godot games — on my own infrastructure.

2024 – 2025

Hermes Deutschland Senior Software Developer · Hamburg

Rebuilt the live-monitoring frontend on a consolidated TanStack stack, shipping at least two releases per two-week sprint.

Frontend error rate (Sentry) down more than 20%
Test coverage in core modules up from 5% to 65% — regressions per sprint down from 4 to 1
Monitoring-widget load time cut from 10+ s to 1–2 s by reworking Kafka-stream data preparation

2019 – 2023

Finanzcheck Senior Software Developer · Tech & Process Lead · Hamburg

Scaled the credit-request frontend and landing pages; built and established the team's Material-UI component library.

Feature lead time down from 14 days to 5
UI feature implementation time halved by the component library

2018 – 2019

Lokalportal Senior Software Engineer · Hamburg

Migrated the frontend from Angular.js to React; introduced image-regression testing with Puppeteer.

2017 – 2018

Stylelounge Senior Software Architect · Hamburg

Owned the frontend architecture of the e-commerce platform; introduced React, component-based development and behaviour-driven testing.

2014 – 2016

Cleverbridge Senior Frontend Developer · Köln

Built up the team that moved the entire e-commerce price calculation to microservices — Docker, Kubernetes, Node.js, eventual consistency on Redis, Cassandra and RabbitMQ.

2002 – 2014

Questback Senior Frontend Developer · Köln

Twelve years on one product: the survey platform's frontend — a mobile-first, responsive questionnaire system with a drag-and-drop editor, plus UX and icon design.

— 20 years of shipping —

2026Trade Journal, MCP servers, this site
2023Godot 4 games — a survivors-like, a merge-roguelike
2013CSS-only survey-UI redesigns at Questback
2011an HTML slide-deck engine, keyboard- and swipe-driven
2008BeSlimed — a match-the-slimes browser game
2007canvas experiments, back when canvas was brand new

> browse the full archive [2007–2026]

— get in touch —

work@markus-dethlefsen.de

CV (PDF) available on request.