01 · Zenarios
A financial planner that forecasts a household's money, month by month, for life.
Built alone, from the simulation engine to the App Store listing: tax rules for 38 countries and a whole life in one forecast.
Software engineer · Munich
Constantin Metz
I build products end to end: the engine, the interface, and the film that launches them.
1,000 futures
Then it throws a thousand different markets at the plan.
Fat-tailed returns and drifting inflation, drawn a thousand times, each draw seeded and reproducible. Each line is one future. In 985 of these 1,000, the money lasts.
Real engine output · the app's example household · engine 5.7.0
App Store · web
Free on iPhone, Mac and the web, in seven languages.
No account, no ads, and the plan never leaves the device.
02 · Signals
It notices what Reddit starts talking about before it trends.
Every comment in 45 subreddits, counted like words: a log-odds score for what is rising today, Theil–Sen and Mann–Kendall for what grows over months.
Lead–lag
And it learns which communities talk about things first.
Leader-to-follower edges between subreddits, tested for direction and turned into early warnings, then scored by replaying trends planted in the data.
An illustration · drawn on the real configuration of 45 subreddits
LiveTranslate
And one that listens: a talk, captioned live in three languages.
The browser's microphone streams to Deepgram over a WebSocket, DeepL translates each finished line, and every line types itself out on screen.
A live caption in German, English and Portuguese:Schön, dass ihr da seid.Great to have you here.Que bom que vocês estão aqui.
03 · PaperScores
An AI reviewer that grades medical research before you trust it.
Papers scored 0–100 on six dimensions, with checklists aligned with CONSORT and related standards, and findings that point to the page they came from, where there is one.
- Methods20
- Statistics15
- Transparency10
- Bias & integrity40
- External validity30
- Significance65
A real scorecard: a narrative review, low on methods by design. The paper isn't named.
Overall score: 30/ 100
04 · Origins
It started with a Minecraft server network.
At school I built its web services: a component library, key redemption, and the sign-in.
OpenID Connect
One sign-in for the forum, the website and the game.
A hand-rolled OpenID Connect provider on the forum's legacy XenForo accounts: consent screens, rate limits, a key pair per client and signed RS256 tokens.
Open source
Then Sequelize: on the maintainers team as it moved to TypeScript.
Reviews, typings, and #13710, which moved the library's errors to TypeScript: +731 −616 across 41 files.
05 · History
Self-taught, and shipping since school.
A first engineering job at 18, senior a year later, and products end to end since. The full story, with names, is on the history page.
- EarlyHTML, CSS, JavaScript; Java for Minecraft mods
- 2018Internships during school: Django, Angular
- 2020First engineering job: React widgets, Storybook, CMS sites
- 2021Senior engineer: an offline-capable PWA for in-store kiosks
- 2023Marketplace apps for Jira: React, Node, .NET, an Nx monorepo
- 2026AI quoting for industry at a YC startup; Zenarios ships
More things I've built
Smaller projects, each with a write-up.
- Stet
A Fictionary party game for phones, set as a dictionary page under a proofreader's red pen.
stet.metz.uk - Unterm Strich
What a car really costs in Germany: every way of getting around, priced month by month, with the answer on the last line.
unterm-strich.metz.uk - Travel cost calculator
A trip budget planner with what-if scenarios, where GPT-5 suggests the cost items and plain code does the maths.
- segno
A Deno port of validator.js from 2020: 73 string validators with TypeScript types, tests, docs and releases.
segno.js.org
Writing
How the thread works, and other notes.
- How the Thread works
One line of light through 3D space, driven by native scroll: the raw WebGL2 renderer, the camera and the data behind the metz.uk home page.
- Building an OpenID Connect server at 18
Christmas 2019: single sign-on for a Minecraft network, on its forum's accounts. What it needed, what I built in three weeks, what held up, and how I'd grow it today.
- 1,000 market futures in a pure-TS engine
How Zenarios simulates up to 1,000 market futures on the phone: Student-t returns, AR(1) inflation, a seeded generator per trial and US market history.