# Form Fields

Fields are the fundamental unit of data in Feathery. A field can be used to collect a piece of information from one of your end users.

Field IDs must be unique across all fields and across forms. Make sure to give your field a readable name so you can easily identify it. The max length of a form or hidden field ID is 128 characters.

## Form vs Hidden Field

Feathery supports two types of fields, **form fields** and **hidden fields**.

### [Form Fields](/platform/build-forms/elements/fields.md)

Form fields are the fields visible to your end users who fill them out. These are added to your form from the visual editor as [text fields](/platform/build-forms/elements/fields/text-field.md), [dropdowns](/platform/build-forms/elements/fields/dropdown.md), [file uploads](/platform/build-forms/elements/fields/file-upload.md), and more.

### [Hidden Fields](/platform/form-fields/hidden-fields.md)

Hidden fields are fields that your end users don't directly fill out, but they can be used to control the behavior of your form and run custom logic. [Learn more](/platform/form-fields/hidden-fields.md)

## Resources

* Different ways to set a field value
* [Link a field across multiple forms](/platform/form-fields/link-fields-across-forms.md)

They can be populated via an integration like [Plaid](https://www.feathery.io/integrations/plaid), set via our [API](https://api-docs.feathery.io/#create-field-value-for-user) or [embed SDK](/develop/react.md), and even passed in through Feathery-hosted form URLS. The structure of field values set from our hosted form URLs looks like `form.feathery.io/to/<form slug>/?<field-id>=<field-value>`. To specify multiple values for a given field, you can specify the query parameter in the URL multiple times.


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