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Original: Simon Willison · 25/02/2026

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Summary

tldraw is moving its test suite to a private repository due to concerns over open source libraries being replicated, highlighting risks for commercial models.

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Key Insights

“a comprehensive test suite is enough to build a completely fresh implementation of any open source library from scratch” — Discussing the implications of test suites for open source projects.
“tldraw aren’t technically open source - their custom license requires a commercial license if you want to use it in ‘production environments’” — Clarifying the licensing status of tldraw.

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Topics

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Full Article

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”.

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Originally published at https://simonwillison.net/2026/Feb/25/closed-tests/#atom-everything.