What Five Days Of Building A Retirement Countdown Taught Me About AI Coding Agents

🔍 Read the full analysis: What Five Days Of Building A Retirement Countdown Taught Me About AI Coding Agents on ThorstenMeyerAI.com

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Developer Thorsten Meyer says he built Altersteilzeit, a free web app that counts working days around German partial retirement, with help from an AI coding agent over five days. His account, published October 13, describes a project that grew from a short animated film into a public site with a daily countdown, a film, games and multilingual audio — while Meyer retained responsibility for the product decisions and release approvals.

Meyer says he began on September 28, 2026, by asking the agent to make a one-minute animated film about the working and non-working phases of German Altersteilzeit in the block model. By October 2, he says, the public app included a daily working-day count, milestones, a countdown film, games, language options, a team countdown, a bridge-day finder and legal pages. The account says the project had 24 commits, each co-authored by Claude Opus 5.5.

Users enter the start date of either phase and choose a model, which Meyer says ranges from 1:1 to 5:5. The app calculates the other date and counts Monday-to-Friday working days, subtracting public holidays for the relevant German federal state and leave entered by the user. Meyer describes the site as browser-based, with no accounts, cookies or tracking; shared dates are kept after the “#” in a web address, which he says is not sent to a server.

The project expanded through successive builds: Meyer says the agent worked on the film, date calculations, 3D game prototypes, translations, a mobile scrolling fix, narration, sound effects and deployment. His account lists about 18,000 lines of JavaScript and Python, 15 test scripts, 1,224 voice clips and 17 sound effects. It also describes 19 game concepts, although an earlier passage refers to 15 playable modes, leaving the precise game count and mode count unclear.

Where the Agent Helped Most

The account offers a practical example of how an AI coding agent can contribute across a small software project, not just generate an isolated code sample. Meyer describes using it for implementation, testing, localization and production tasks, including coordinating parallel work on translations and preparing assets for release. That breadth is relevant to developers evaluating whether agents can help move a prototype toward a public product.

But the project’s pace and scope are Meyer’s account of one build, not an independent benchmark of coding-agent performance. He says he set the concept and tone, made choices about voices and dialects, checked the results and approved releases. The distinction matters: the reported output does not establish that an agent independently delivered the product or that the same timeline would apply to other projects.

The app also illustrates how a narrow personal use case can shape product decisions. Its calculations depend on dates, work schedules, regional holidays and entered leave, while its presentation turns those figures into a film and games. That combination may make a countdown more engaging, but the source does not provide user numbers, independent testing of the calculations or evidence of wider adoption.

From Film Prompt to Public App

Altersteilzeit is a German partial-retirement arrangement. 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 model, for example, has four years in each phase. The app is designed to count the remaining working days rather than simply the calendar days.

Meyer says the first request was deliberately small: an animated film showing the two phases. Over the following days, the project added the daily view, games and supporting tools. Its game design uses calendar time as gameplay structure: the account gives examples such as months forming maze columns and working days appearing as emails. Meyer also says game names were chosen to avoid other companies’ trademarks.

The source is a first-person project account by the developer, published on ThorstenMeyerAI.com on October 13, 2026. It reports the build timeline, feature list and development workflow, but does not include independent verification or outside user feedback.

“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 Build Account Does Not Show

The source does not provide independent technical verification of the app’s calculations, privacy design, test coverage or performance. It also gives no user figures, outside reviews or information on whether the app has been used for real retirement planning. The features and production totals should be understood as claims in Meyer’s own account.

Some scope details are inconsistent: one passage says the app has a 3D game with 19 ways to play, another describes 15 modes, and the day-by-day account mentions adding 12 games. The source also refers to seven languages and five German dialects in one section, then says narration was produced in seven languages before five dialects were added. It does not reconcile these counts or specify the exact language coverage of every feature.

The account names Claude Opus 5.5 and dates the work to September and October 2026, but provides no model documentation, prompts, cost figures or detailed breakdown of how much code was generated versus revised by Meyer. The reported five-day schedule therefore cannot, on this evidence alone, be compared directly with other development projects.

The App’s Next Test Is Use

Meyer’s account says the site was public by Friday, October 2, but it does not announce a later release milestone or describe planned updates. The next useful evidence would be how the app performs for users, whether its holiday and leave calculations hold up across German states, and whether the privacy claims are independently reviewed.

For now, the reported development is complete enough to present as a public web app, while its longer-term maintenance and adoption remain unknown. Meyer’s account suggests that future assessment should look beyond the amount produced in five days: it should also examine the reliability of the calculations, the quality of the agent’s work and the human review needed before release.

Key Questions

What is Altersteilzeit?

Altersteilzeit is a German partial-retirement arrangement. 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?

Users enter the start date of one phase and select a model. The app calculates the other date and, according to Meyer, counts weekdays while subtracting relevant state public holidays and user-entered leave.

How long did the project take?

Meyer says work began on September 28, 2026, and the public app was ready by October 2, a five-day period.

Did the AI agent make all the product decisions?

No. Meyer says the agent handled coding and production tasks, while he chose the concept and tone, reviewed outputs and approved releases. The account does not provide an independent audit of how the work was divided.

Is the app’s privacy and accuracy independently verified?

The source says the app has no accounts, cookies or tracking and calculates dates in the browser. It does not provide an independent security review or external verification of the working-day calculations.

Source: ThorstenMeyerAI.com