How I Built A Retirement Countdown With An AI Coding Agent In Five Days

🔍 Read the full analysis: How I Built A Retirement Countdown With An AI Coding Agent In Five Days on ThorstenMeyerAI.com

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Thorsten Meyer says he built and released Altersteilzeit, a free web app for people counting down to retirement under Germany’s partial-retirement system, in five days with help from the Claude Opus 5.5 AI coding agent. The project began on September 28, 2026, as a request for a short animated film and had grown by October 2 into a countdown, a collection of games and other tools; Meyer says he directed the work and approved the release.

Altersteilzeit refers to partial retirement. In the block model described by Meyer, a person works as usual during an active phase and is then released from work for an equal-length passive phase; a 4:4 arrangement, for example, has four years in each phase. The app asks users for a start date and a model, from 1:1 to 5:5, then calculates the other date and remaining working days. Meyer says its calculation accounts for weekdays, public holidays in the user’s German federal state and entered leave.

The app combines that calculation with a daily view showing the countdown, a progress ring, a saying and upcoming milestones. Meyer also lists a short film, calendar exports, a printable calendar, a bridge-day finder, badges, a team countdown and a 3D game collection. His account describes 19 ways to play, although a day-by-day section separately says the games were expanded by 12 during development; the piece does not explain that difference.

Meyer says all 24 commits were co-authored by Claude Opus 5.5. He describes the agent writing code, testing features, documenting work and deploying the site. He provided direction, made product and editorial choices, reviewed the results and approved the release. The article also reports 15 test scripts, 1,224 voice clips and 17 sound effects, but does not provide independent verification of those figures.

Where the Developer Stayed in Control

The account offers a concrete example of how an AI coding agent can be used across a small software project, from early prototypes to a public release. Meyer says the agent took on implementation and production tasks, including building browser-based 3D games, preparing translations and generating audio assets. Those descriptions are his report of the project, not a controlled measure of how much time or cost the agent saved.

The division of work he describes also shows what remained with the person directing the project: setting its purpose and tone, choosing voices and dialects, deciding how the film should feel, reviewing the output and approving publication. For readers considering similar tools, the account is useful as a description of one workflow, but it does not establish that another developer could reproduce the same scope or pace.

From Film Request to Public App

Meyer says the initial request on Monday, September 28, was for a short animated film counting down working days in a German Altersteilzeit block model. Work expanded over five days. His timeline says the first day brought the film, date calculations, personal date entry and game prototypes; by that evening, he says the site was online with legal pages. Subsequent days added a daily view, languages, games, badges, audio and other tools.

One issue emerged during development: Meyer says a change caused pages to stop scrolling on an iPhone, prompting a hotfix. By October 2, he says he had approved the release and added five German dialects with voices. His October 13 article presents the app as the result of that collaboration and focuses on what he says the AI agent handled versus what required his direction and approval.

“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

What the Account Does Not Verify

The project’s details come from Meyer’s own article. It does not include an independent technical review, user data, a download or traffic figure, or a comparison of development time with a version built without an AI agent. Claims about the app’s features, code, tests, audio production and deployment should therefore be read as the developer’s account.

There is also a discrepancy in the description of the game collection: the opening says there are 19 ways to play, while the development timeline says the game additions included four on day two and 12 on day three, after two prototypes on day one. The article does not explain how those counts relate. It also does not specify how the app’s holiday data is sourced or how users should verify date calculations for their individual circumstances.

The Published App and Its Limits

Meyer’s article describes Altersteilzeit as a public website, but it does not name a future development milestone or give a schedule for updates. Readers can use the account to understand the app’s stated features and development process; they should check the live site for current availability and details.

For anyone relying on the countdown for planning, the app’s calculations should be checked against official holiday information and the terms that apply to their employment arrangement. The source does not say whether the project will receive further updates, add features or publish independent testing results.

Key Questions

What is Altersteilzeit?

Altersteilzeit is a form of partial retirement in Germany. In the block model described by Meyer, a person works during an active phase and then has a passive phase away from work.

What does the app calculate?

Meyer says users enter a phase start date and a model from 1:1 to 5:5. The app calculates the other date and counts working days, taking account of weekdays, federal-state public holidays and leave entered by the user.

How long did the project take?

Meyer says development ran from September 28 to October 2, 2026, moving from an initial film request to a public web app.

Did the AI agent build the app without human involvement?

No. Meyer says the agent wrote and tested code and supported production work, while he set the direction, made choices, reviewed outputs and approved releases.

Are the development claims independently verified?

The source is Meyer’s account of his own project. It does not include an independent audit, user statistics or a controlled comparison with development without an AI coding agent.

Source: ThorstenMeyerAI.com