What isolation level does SQLite provide, compared to other RDBMS?

SQLite effectively provides serializable isolation for its transactions — the strictest standard isolation level — rather than offering a configurable choice of levels (read committed, repeatable read, serializable) the way many client-server databases do.

flowchart LR
    A[Transaction begins] --> B[Sees a consistent snapshot]
    B --> C[No other transaction's uncommitted changes visible]
    C --> D[Commit only succeeds if no conflicting write occurred]

In practice this is achieved through SQLite's locking model (or WAL's snapshot mechanism): a reader never sees another transaction's uncommitted writes, and a writer can't commit if it would conflict with changes made since its transaction began. There's no equivalent to loosening this to a weaker isolation level for performance, the way you might deliberately choose READ COMMITTED in PostgreSQL — SQLite's transactions are serializable by default and don't offer that particular tradeoff knob.