Simon WillisonSunday · July 19, 2026FREE

SQLite Query Explainer

Simon Willison announced the SQLite Query Explainer, a browser-based tool that lets users run SQL queries against a SQLite database and see annotated explanations of how SQLite executes them. The tool runs SQLite in Python via Pyodide in WebAssembly, enabling client-side execution. It annotates every line of both `EXPLAIN QUERY PLAN` and the low-level `EXPLAIN` bytecode output with plain-English descriptions of what the query planner and virtual machine are doing. Willison was inspired by Julia Evans' post "Learning a few things about running SQLite" where she expressed difficulty reading query plans. He used Fable to build the interactive explain tool. Willison notes he does not know enough about SQLite query plans to verify the results himself, but considers the explanations "cromulent enough." The tool is intended to help developers understand SQLite's query execution internals.