OPFS + Pyodide test harness

Simon Willison · Simon Willison · 2026-06-23

Simon Willison builds an OPFS and Pyodide test harness playground using Claude Code to explore whether Datasette Lite can edit persistent SQLite files stored in the browser via the Origin Private File System.

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Appears in

Simon Willison's AI-Augmented Datasette Ecosystem: Agent, Apps, and Plugins

Extraction

Topics: pyodidewebassemblybrowser-storagedatasette-lite

Claims

Datasette Lite runs the full Python Datasette application entirely in the browser using Pyodide and WebAssembly.
The Origin Private File System (OPFS) could enable browser-based editing of persistent SQLite files stored on the user's computer.
Willison used Claude Code to build a playground UI for testing OPFS compatibility across different browsers.

Key quotes

I've been pondering if Datasette Lite - the Python Datasette application run entirely in the browser using Pyodide and WebAssembly - might be able to edit persistent SQLite files stored on the user's computer.