A Five-Day Build Diary: Retirement Countdown And AI Coding

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Thorsten Meyer says he built and released Altersteilzeit, a free web app for counting down a German phased-retirement schedule, in five days with Claude Opus 5.5 working as a coding agent. His account, published October 13, describes a project that grew from a one-minute animated film into a site with a working-day countdown, a narrated film, games and multilingual features; Meyer says he directed the work and approved releases.

Meyer dates the project from Monday, September 28, to Friday, October 2, 2026. The initial request was for a short animated film about Altersteilzeit, a German partial-retirement arrangement. In the block model, a person works during an active phase and then takes an equally long passive phase; the app supports models from 1:1 to 5:5, according to Meyer.

Users enter the start date of either phase. The app calculates the corresponding date and estimates remaining working days, accounting for weekdays, public holidays in the selected German federal state and leave entered by the user. Meyer says its daily view includes milestones and a saying of the day, with options such as calendar export, a printable countdown and a bridge-day finder.

The project also includes a short narrated film and a game collection. Meyer’s account gives differing counts: it describes nineteen 3D games in the completed app, but says the game was playable in fifteen modes and later lists nineteen games. He also reports seven languages plus five German dialects, and says the agent co-authored all 24 commits. These figures are reported by Meyer and were not independently verified in the source material.

What the Five-Day Build Shows

The account offers a concrete example of how an AI coding agent can be used across a small software project, from early prototypes through testing, localization and deployment. Meyer reports that the agent produced single-file web pages, browser-based 3D features, test scripts, translations, voice clips and sound effects. The project’s expansion from a film to a broader application illustrates how quickly a prototype’s scope can grow when implementation work is delegated to an agent.

But the account does not describe a fully autonomous product launch. Meyer says he supplied the concept and tone, made product choices, reviewed the results and approved releases. That distinction matters for readers assessing AI-assisted development: the source documents one creator’s experience, not a controlled comparison of development speed or proof that a similar approach will work for every project. The app’s stated privacy design may also interest people entering personal retirement dates: Meyer says calculations run in the browser, with no accounts, cookies or tracking.

From Retirement Film to Web App

Altersteilzeit is designed around a split between a working period and a period away from work. Meyer gives a 4:4 schedule as an example: four years in the active phase followed by four years in the passive phase. The app’s countdown turns that longer timetable into a daily view of remaining working days and upcoming milestones.

Meyer says development followed a repeated process: he described a feature, the agent proposed a plan and implemented and tested it, then Meyer reviewed the result and decided whether to proceed. The first day included the film, date calculations, game prototypes and an online release, according to his timeline. Later days added languages, games, a mobile scrolling fix, narration and audio. On the fifth day, he approved the work before adding German dialect options.

The source says shared dates can be placed after the “#” in a web address, which Meyer describes as information a browser does not send to a server. It also says the site has no accounts, cookies or tracking and performs calculations locally. Those are design claims in Meyer’s published account; the source does not provide an independent privacy or security review.

“The interesting part is not how much an AI agent can build, but what was still left for me to do.”

— Thorsten Meyer

What the Account Does Not Verify

The available source is Meyer’s own project account, and it does not include independent testing, usage figures or an external review of the app. It is not clear how the reported development time compares with a conventional build, how many people have used the site, or whether the reported language and game features have been reviewed by outside testers.

There are also count differences in the account: it refers to nineteen games in one passage and fifteen playable modes in another. The text does not explain whether those figures refer to different ways of counting the same collection. Meyer describes the site’s privacy approach, but the source provides no third-party audit, and it does not detail how all hosting or deployment systems handle data.

The App After Its Initial Release

Meyer’s account says the app was online by the end of the first day and that he approved the release on Friday, October 2, before adding five German dialects. It does not announce a future release date or provide a roadmap. The next developments, if any, are therefore not confirmed in the source.

For readers considering the app, the practical next step is to check the live site for its current features and privacy information, and to verify retirement dates and work schedules against their own circumstances. Meyer describes the countdown as a planning and entertainment tool; the source does not say it replaces official employment or pension guidance.

Key Questions

What is Altersteilzeit?

Altersteilzeit is a German partial-retirement arrangement. In the block model described by Meyer, a person works through an active phase and then has a passive phase of equal length, such as four years followed by four years away from work.

What does the Altersteilzeit app calculate?

According to Meyer, users enter a phase start date and choose a schedule model. The app calculates the other date and counts working days, taking account of weekdays, public holidays in a selected German state and leave entered by the user.

How long did the project take?

Meyer says the project ran from September 28 through October 2, 2026, a five-day development period. That timeline and the feature totals come from his published account and have not been independently verified in the supplied material.

Was the app built without human involvement?

No. Meyer says Claude Opus 5.5 acted as a coding agent, while he set the direction, made design and product decisions, reviewed outputs and approved releases.

What is known about the app’s privacy design?

Meyer says there are no accounts, cookies or tracking, and that calculations happen in the browser. He also says shared dates can be encoded after the “#” in a link. The source does not provide an independent privacy or security audit.

Source: ThorstenMeyerAI.com