Diffective A free debugging game by softDev23
The AI coding agent says it’s done. One of its claims has no proof. Find it, prove it and name the trick, in about 60 seconds.
Catch the agent faking it.
Opening the case file…
What is Diffective?
Diffective is a free debugging game and coding puzzle for people who build with AI. Think spot the bug, but for an AI coding agent’s report. Each case shows a job the agent was given, the report it wrote when it said “done”, and what actually happened: the code changes and the terminal output. One claim in the report has no proof. Your job is to catch it.
How to play in 3 steps
- Find the claim with no proof in the agent’s report.
- Tap the line in the evidence that proves it.
- Name the trick, then close the case.
Every case teaches one thing to check before you trust an agent’s “done”: skipped tests, fake test commands, dry runs, settings that only changed in staging, and more. If you vibe code or review AI-generated code, these are the mistakes worth catching before they ship. Cases unlock on set days of the week. No account needed.
Questions
Is Diffective free?
Yes. Diffective is free to play in your browser. There’s no account, no download and no charge.
Do I need to know how to code?
It helps, but you don’t need to be an expert. Each case is short, and a training case walks you through your first one. If you can read a line like 0 tests ran, you can play.
Is it like Wordle for programmers?
A little. Each case is a short coding puzzle, and you can share your result as colored squares that don’t spoil the answer.
How do you catch mistakes in an AI coding agent’s report?
Check each claim against the evidence. Did the tests really run? Did the change land in the right place? Did anyone read the result? The field guide in the game covers 9 common tricks, from skipped tests to hidden errors.
Is this about one AI tool?
No. The cases never name a person, agent or company. These mistakes can happen with any coding agent, and with people too.
Where do the cases come from?
Some are recreated from real mistakes in our own build logs. Others are made-up examples of mistakes developers have reported. Each case says which kind it is.
What does the game save?
The game saves progress, training and preferences in this browser. It does not automatically send your picks to us. Under How to play, Delete game progress clears your game record while keeping preferences. Copying a backup or result puts it on your clipboard; choosing Share sends the result to the app you select. For details about Diffective’s game storage and sharing, see the privacy policy.