The Lessons Behind My Five-Day AI Coding Agent Project

🔍 Read the full analysis: The Lessons Behind My Five-Day AI Coding Agent Project on ThorstenMeyerAI.com

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Thorsten Meyer says he built and released Altersteilzeit, a free web app for counting working days until partial retirement, in five days with help from an AI coding agent. In an account published Oct. 13, he describes the agent’s role in producing the app’s countdown, film, games and multilingual features—and says he retained responsibility for the concept, product decisions and release approvals.

Meyer’s project began on Monday, Sept. 28, 2026, with a request for a short animated film about the working and non-working phases of German Altersteilzeit in the block model. By Friday, Oct. 2, he says, the public app included a daily countdown, a narrated film, a 3D game collection, a team countdown, a bridge-day finder and badges. The account describes 19 game options, seven languages and five German dialects. The source also refers to fifteen game modes, so the exact distinction between games and modes is not fully explained.

Users enter the start date of either phase and select a model from 1:1 to 5:5. The app calculates the other date and estimates remaining working days, accounting for weekdays, public holidays in the user’s German federal state and entered leave, Meyer writes. It also offers milestone calendar exports, a printable calendar and a daily view with a progress ring and saying of the day.

Meyer says all 24 commits were co-authored by Claude Opus 5.5, which he describes as the coding agent. He reports that it generated about 18,000 lines of JavaScript and Python, 15 test scripts and 1,224 voice clips, alongside sound effects, translated text and deployment work. These figures and descriptions come from Meyer’s project account; it does not provide an independent technical audit.

Where the Agent’s Work Ended

The account offers a practical example of AI-assisted software development that goes beyond generating a code snippet. Meyer describes a workflow in which the agent planned and built features, ran tests, recorded its changes and helped deploy updates across several days. The project’s reported breadth—games, narration, localization and a public website—shows the range of tasks one developer may attempt with an agent.

But the account does not present the agent as an independent product owner. Meyer says he supplied the initial idea and tone, chose features and voices, reviewed outputs and approved releases. That distinction matters to readers weighing what such tools can do: rapid production did not remove the need for human direction and review, and the source does not establish how the project’s speed or quality compares with a conventional development process.

Meyer also says privacy shaped the design: no accounts, cookies or tracking, with calculations done in the browser. Shared dates are placed after the “#” in a web address, which browsers do not send to servers in the same way as the part before it. That design choice may interest users entering personal schedule information, although the account does not include a third-party privacy or security assessment.

From Countdown Film to Public App

Altersteilzeit is a form of partial retirement in Germany. In the block model described by Meyer, a person works their usual schedule during an active phase and then stops working during a passive phase of equal length; a 4:4 arrangement, for example, pairs four years in each phase. The app turns that timeline into a count of working days rather than simply showing calendar days.

The project grew from a small creative request. Meyer says the first goal was a one-minute animated film, but he and the agent added date calculations, a daily dashboard and games over five days. In his account, development proceeded through 16 versions, with features added or revised daily. A reported iPhone scrolling problem prompted a hotfix on the third day.

The games use calendar time as their structure: Meyer describes months, weeks, working days and quarters as game elements, with entered leave affecting play. The project also includes German dialect versions and spoken audio. Those details make this a report about one specific build, not evidence that every coding agent will produce comparable results from a similar prompt.

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

— Thorsten Meyer, describing the project’s central lesson

What the Account Does Not Verify

The figures in Meyer’s article—including the number of commits, lines of code, translations and voice clips—are the author’s own account. No independent review, code repository analysis or performance comparison is supplied. The source also does not detail the agent’s error rate, how much generated work required revision, or whether all features were tested across supported devices and languages.

There is a discrepancy in the game descriptions: the article says the app has 19 games in one passage, but later says the game is playable in 15 modes. It does not explain whether some games contain multiple modes or whether the figures describe different versions. The source identifies Claude Opus 5.5 as the co-authoring agent, but does not provide model-provider confirmation or further information about its setup.

The account reports that the site went online and was free, but does not give usage figures, user feedback, ongoing maintenance plans or the app’s current availability beyond the publication date. Its privacy description is also Meyer’s characterization, not a published independent security review.

The App’s Next Test Is Use

Meyer’s Oct. 13 account does not announce a new release date or specific upcoming feature. The immediate next measure of the project will be whether the public app continues to work reliably as users enter different dates, leave allowances and regional holidays. The article does not say whether Meyer plans to publish updates or respond to reported problems.

For readers interested in the development process, further evidence would include a public code review, documentation of testing across devices and languages, and clearer accounting of how the 19 games relate to the 15 modes. Meyer’s account establishes what he says was built and how he describes the collaboration; broader conclusions about agent performance would require more projects and independently checkable results.

Key Questions

What is Altersteilzeit?

Altersteilzeit is a German form of partial retirement. In the block model described by Meyer, a person works during an active phase and then has a passive phase of equal length.

What does the app calculate?

Users enter the start date of one phase and choose a model. Meyer says the app calculates the other date and counts working days, taking weekdays, regional public holidays and entered leave into account.

What did the AI coding agent do?

Meyer says Claude Opus 5.5 helped write and test code, build features, produce translated text and audio, and support deployment. These details are reported by Meyer and have not been independently audited in the source.

What decisions did Meyer keep?

Meyer says he set the concept and tone, chose product details such as voices and dialects, reviewed the work and approved releases. He presents human judgment and sign-off as continuing parts of the process.

Was the app independently reviewed?

The account does not cite an independent technical, security or privacy review. Meyer says the app has no accounts, cookies or tracking and calculates information in the browser, but those claims are not independently verified in the source.

Source: ThorstenMeyerAI.com