Limits of Material-UI Autocomplete freeSolo prop regarding built-in validation

Direct answer

With freeSolo set to true, Material‑UI’s Autocomplete treats the text field as a pure string source: whatever the user types is forwarded unchanged to onInputChange and onChange. The component does not automatically check whether that string matches an option or conforms to any rule, and there is no built‑in validation prop that could be enabled by default.

Why existing props don’t validate

• isOptionEqualToValue only determines how a selected option is compared to the current value for highlighting; it never rejects free‑typed input.
• filterOptions merely shapes the list of options shown in the popup; it does not constrain the text field’s value.

Steps to add validation yourself

1. Keep the Autocomplete controlled (or use local state) so you receive the entered string in onChange.
2. In the handler, test the value against options or a custom validator.
3. If the test fails, set an error state and pass error and helperText to the rendered TextField via renderInput.
4. Leave isOptionEqualToValue and filterOptions unchanged; they continue to work for option selection and display.

This approach keeps validation in application code, avoids any automatic mutation that could confuse screen readers, and imposes no performance cost on components that do not need it.