Interactive SQLite Query Explainer runs in-browser with annotated query plans

Simon Willison released an interactive SQLite Query Explainer that annotates SQLite’s EXPLAIN and EXPLAIN QUERY PLAN outputs with plain-English descriptions of what the query planner and virtual machine are doing. The tool runs entirely in the browser by executing SQLite via Python in Pyodide inside WebAssembly, so no server component is required.

The project was inspired by Julia Evans’ post titled Learning a few things about running SQLite, in which Evans noted the difficulty of learning to read a query plan. Willison commissioned an AI agent named Fable to build the interactive tool, which layers explanations over the raw query plan outputs.

Willison cautions that he does not personally verify the correctness of the explanations due to limited expertise with SQLite query plans, but considers the tool "cromulent enough" for practical use. The tool is available on Willison’s tools site and operates client-side, meaning queries and data never leave the user’s browser.