Simon Willison built a browser-based test harness to explore whether Datasette Lite, a full Python Datasette instance running via Pyodide and WebAssembly, can read and write persistent SQLite files using the Origin Private File System API.
OPFS gives browser applications a sandboxed, origin-scoped filesystem with synchronous access from worker threads, making it a credible path to persistent local storage for WebAssembly workloads. The harness itself was generated by Claude Code and exists specifically to test cross-browser behavior, which is where OPFS support still varies.
The tool is worth examining directly because the interesting question is not whether this works in Chrome. It is whether Pyodide running in a worker can get synchronous OPFS access in Firefox and Safari, which would determine whether Datasette Lite can become a genuinely local-first SQLite editor without a server.
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