The browser checks SQLite's standard SQLite format 3 file header before loading the database. It then creates an in-memory copy for the WebAssembly engine, lists user tables and views, and shows a bounded 500-row preview. Search and pagination work on the loaded preview, while the SQL panel handles focused inspection.
Your original file is never rewritten. Each SQL run uses a disposable snapshot with query-only mode enabled, so the database you are browsing stays unchanged even if a query alters its own temporary state.