a few weeks ago I wanted to see if Opus 4.5 could build and improve upon a real open source library from scratch.

so I specced out globlin, a drop-in replacement for glob v13. up to 7.5x faster than glob, and up to 3.2x faster than fast-glob. all powered by Rust.

I defined the architecture, the API surface, every edge case I could think of: broken symlinks, extglobs, Windows drive letters, cyclic directories, permission errors.

kept asking Opus to poke holes until there were none.

then I let it cook.

158 commits. 21,000 lines of code. 1,451 tests across 53 files. cross-platform CI. all green.

it wrote fuzz tests. property-based tests. UNC path tests. macOS sandbox tests. more thorough than most human-written test suites I've seen.

npm install globlin, drop it in, done.

fully open source and MIT licensed under the Cap umbrella.

I don't know how to feel. this is insane. it works.