For developers

FillKite has filters and actions for the parts that matter. Some examples:

Hooks
Hook	Type	Use it to
`fillkite_before_save_entry`	Filter	Change an entry, or return a `WP_Error` to stop it. Receives `$entry, $form`.
`fillkite_after_save_entry`	Action	Run code after an entry is saved. Receives `$entry, $form`.
`fillkite_entry_status_changed`	Action	React when an entry moves to Replied, Won and so on.
`fillkite_register_fields`	Action	Register your own field types.
`fillkite_notification_email`	Filter	Change an email before it is sent.
`fillkite_merge_tags`	Filter	Add or change merge tags.
`fillkite_webhook_payload`	Filter	Change what a webhook sends.
`fillkite_spam_check`	Filter	Add your own spam check. Return a reason to mark the entry as spam.
`fillkite_rate_limit`	Filter	Change the rate limit for a form.
`fillkite_disposable_domains`	Filter	Add or remove blocked email domains.
`fillkite_client_ip`	Filter	Read the visitor’s IP from a proxy header.
`fillkite_submission_redirect`	Filter	Send the visitor somewhere else after submitting.
`fillkite_render_field`	Filter	Change a field just before it is shown, such as disabling a full choice.
`fillkite_form_gate`	Filter	Show something else in place of a form.
`fillkite_confirmation_message`	Filter	Change the thank-you message.
`fillkite_lead_quality`	Filter	Change an entry’s lead quality.
`fillkite_spam_phrases`	Filter	Add phrases the spam score looks for.
`fillkite_app_tabs`	Filter	Add your own screen to the FillKite header. Each tab is `label`, `url` and `cap`, with an optional `badge` count.
`fillkite_app_plan`	Filter	Change the plan chip in the header. Return `label` and `pro` (true or false).
`window.fillkite.holds( form, conditions )`	JavaScript	Check whether a set of rules holds for the current answers, so an add-on can build rules on the same engine as field logic.
`LogicEditor`	Prop	Add-on settings cards in the builder receive a `LogicEditor` prop, the same rule editor FillKite uses for field logic.
`fillkite_theme_button_themes`	Filter	Choose which classic themes the Send button follows when Send button look is Automatic. Receives the list of theme slugs.

Example: build your own rules on the same engine

FillKite Pro’s Submit rules are made with two free pieces, and your add-on can use them too. window.fillkite.holds() checks rules in the visitor’s browser, and the LogicEditor prop gives your settings card the same rule editor as field logic.

1. Check rules on the page

Rules are written like field logic: match is all or any, and each rule has a field, an operator and a value. Fields hidden by logic count as unanswered. This example stops the form while an order is not paid:

const form = document.querySelector( '.fk-form[data-fk-form="12"]' );
const rules = {
	match: 'all',
	rules: [ { field: 'f_paid', operator: 'is', value: 'No' } ],
};

form.addEventListener( 'fillkite:beforesubmit', ( event ) => {
	// true when the rules hold for the answers on the screen right now
	if ( window.fillkite.holds( form, rules ) ) {
		event.preventDefault();
		// show your own message here
	}
} );

A set of rules with no rules in it holds for everyone, so check that it has rules before you use it to block anything. Browser checks can be skipped, so check again on the server with the fillkite_before_save_entry filter and return a WP_Error. You can see this in action on the paid order support demo.

2. Add a rules card to the builder

Add a card to the form’s Settings tab with the fillkite.builder.formSettings filter. Your component gets value, onChange, the form’s fields and the LogicEditor:

wp.hooks.addFilter( 'fillkite.builder.formSettings', 'my-addon', ( cards ) => [
	...cards,
	{
		key: 'myRules',
		title: 'My rules',
		description: 'Stop the form when these rules hold.',
		Component: ( { value, onChange, fields, LogicEditor } ) =>
			wp.element.createElement( LogicEditor, {
				field: { id: 'myRules', logic: value },
				fields,
				onChange: ( patch ) => onChange( patch.logic ),
				copy: { title: 'When', toggle: 'Use rules', subject: 'Stop the form if' },
			} ),
	},
] );

On the PHP side, keep your key with the fillkite_form_settings filter so it is saved with the form.

WP-CLI: wp fillkite forms, wp fillkite entries and wp fillkite export.

Every hook has a short description in the plugin’s code.

Credits: the FillKite admin screens use Plus Jakarta Sans and IBM Plex Mono, bundled with the plugin under the SIL Open Font License 1.1.

Last updated: November 4, 2026