> For the complete documentation index, see [llms.txt](https://docs.feathery.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.feathery.io/platform/build-forms/logic/custom-field-validation.md).

# Custom Field Validation

Many Feathery fields come with default validation rules. For example, an email field will validate that its input is a valid email on submission.

You can create additional custom rules to implement other validation checks. For example, you may want to make sure that the user enters different values in two different fields.

<figure><img src="/files/h4gwV4UChUOsSx3bPl2M" alt=""><figcaption></figcaption></figure>

Custom validation rules can be added to any field or button, and they will be run when the step is submitted. If the rule evaluates true, the custom validation message will appear on the element you added the rule to. Step submission and navigation will not occur until the validation error is resolved.

For more complex rules involving multiple possibilities, you can combine multiple comparisons using `AND` and `OR` combinators.

See the detailed discussion of [Logic Conditions](/platform/build-forms/logic/available-conditions.md).


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