Willison built a SQLite query plan explainer in the browser

Willison shipped a SQLite query plan explainer that runs entirely in the browser, no server involved. That matters for anyone debugging slow queries without deep database-internals knowledge, since the tool runs client-side and never sends schema or data anywhere.

Feed it arbitrary SQL against a SQLite database. It shows both EXPLAIN QUERY PLAN and the lower-level EXPLAIN bytecode, with plain-English annotations attached to each line. SQLite compiled to WebAssembly runs the whole thing through Pyodide, executing in Python with no backend at all.

The tool exists because Julia Evans said on July 17 that she still can't read query plans. Willison had Fable build it in response.

Willison also says directly that he isn't expert enough to fully verify the annotations the tool produces. That's the disclosure most AI-built developer tools skip, letting polished output imply an expert already checked it. A query plan explainer is exactly where a confidently wrong annotation does damage. The whole point is helping someone who doesn't already know the answer.