No, it doesn't. By default in sqlite3, you can store whatever you like in whatever field you want.

The "built-in validation mechanism" is invoking json_valid(X) [1] call within the CHECK [2] condition on a column.

[1] https://www.sqlite.org/json1.html#jvalid

[2] also assumes you didn't disable CHECKs with PRAGMA ignore_check_constraints https://www.sqlite.org/pragma.html#pragma_ignore_check_const...