Simon Willison’s Weblog

25th February 2026 - Link Blog

tldraw issue: Move tests to closed source repo (via) It's become very apparent over the past few months that a comprehensive test suite is enough to build a completely fresh implementation of any open source library from scratch, potentially in a different language.

This has worrying implications for open source projects with commercial business models. Here's an example of a response: tldraw, the outstanding collaborative drawing library (see previous coverage), are moving their test suite to a private repository - apparently in response to Cloudflare's project to port Next.js to use Vite in a week using AI.

They also filed a joke issue, now closed to Translate source code to Traditional Chinese:

The current tldraw codebase is in English, making it easy for external AI coding agents to replicate. It is imperative that we defend our intellectual property.

Worth noting that tldraw aren't technically open source - their custom license requires a commercial license if you want to use it in "production environments".

Update: Well this is embarrassing, it turns out the issue I linked to about removing the tests was a joke as well:

Sorry folks, this issue was more of a joke (am I allowed to do that?) but I'll keep the issue open since there's some discussion here. Writing from mobile

• moving our tests into another repo would complicate and slow down our development, and speed for us is more important than ever
• more canvas better, I know for sure that our decisions have inspired other products and that's fine and good
• tldraw itself may eventually be a vibe coded alternative to tldraw
• the value is in the ability to produce new and good product decisions for users / customers, however you choose to create the code