Building a Tetris Time Clock with AI

The year is coming to an end, and looking back I had a lot of fun building quirky, fun, and insightful visualizations. Agentic coding agents have been hugely empowering for me. In 2024 it was "just" autocomplete on steroids. Now it feels more like conducting, directing the agents to go where I please. Often they're impressive; sometimes they fail at the simplest tasks.

Test-Driven Development with Claude Code

What worked particularly well here was a test-driven (TDD) approach. I asked Claude Code to focus only on the algorithm for selecting the next Tetromino (the Tetris blocks), starting with tests. After that, things went smoothly, though it still took many follow-up prompts (around 100) to reach the final result. Good thing that Claude doubled the token limits for paying users over Christmas.

Try It Out

You can visit the countdown here: tetris-time.koenvangilst.nl/?to=newyear

After New Year's, it also works as a regular clock: tetris-time.koenvangilst.nl

If you're impatient, you can increase the speed using URL parameters: tetris-time.koenvangilst.nl/?to=newyear&speed=10

The code is open source and available on GitHub.