> For the complete documentation index, see [llms.txt](https://admin-docs.onestop.site/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://admin-docs.onestop.site/managing-services/managing-forms/using-the-form-builder/field-validators.md).

# Field Validators

Field validators allow you to configure custom validation in a form where input entered by users for that form is validated against your own datasets.

Field validators require you to have an existing [dataset](/databanks/creating-datasets.md) to validate values against.

To create a field validator:

* Go to the form builder and click on the [settings icon](/managing-services/managing-forms/using-the-form-builder.md#field-settings) for the field you want to edit.
* Click on the validation settings tab.
* Click on the "Add Custom Validator" button

<figure><img src="/files/NnszwP9nZwxrqgtolYPg" alt=""><figcaption></figcaption></figure>

* The Custom Field Validator form appears

<figure><img src="/files/n0ZVvrA1shgXlbi0tswx" alt=""><figcaption></figcaption></figure>

* Provide a name for the validator
* Create or select a [dataset connection](/databanks/using-datasets.md#read-dataset-connection)
* Choose a lookup column for the validator. The lookup column is the field in the dataset that the form field value will be compared against.

<figure><img src="/files/ofP5p84J4905UTc6pXHi" alt=""><figcaption></figcaption></figure>

* Provide a custom error message to be displayed to the user when the validation fails.
* Click on the save button.
* You can add as many validators as you require. This ensures you can validate that a user provided value on the form is present in multiple datasets.