Special Fields

FormFast recognizes special hidden fields that customize submission behavior. These fields are extracted before storage — they don't appear in your submission data.

Field reference

FieldDescription
_gotchaHoneypot spam protection. Add as a hidden input — bots fill it, humans don't. Submissions with this field filled are silently marked as spam.
_nextCustom redirect URL after form submission. Must be an absolute URL. Overrides the form's default redirect setting and the default thank-you page.
_subjectCustom subject line for the notification email sent to the form owner. Overrides the default "New submission on {form name}".
_replytoSet the Reply-To address on notification emails so you can reply directly to the submitter. Also used for auto-reply detection.

Usage example

HTML
<form action="https://formfa.st/f/your_endpoint_id" method="POST">
  <!-- Regular form fields -->
  <input type="text" name="name" required />
  <input type="email" name="email" required />
  <textarea name="message"></textarea>

  <!-- Special fields (hidden from the user) -->
  <input type="hidden" name="_gotcha" style="display:none" />
  <input type="hidden" name="_next" value="https://yoursite.com/thanks" />
  <input type="hidden" name="_subject" value="New inquiry from website" />
  <input type="hidden" name="_replyto" value="" />

  <button type="submit">Send</button>
</form>

Dynamic _replyto

Leave the _replyto value empty and use JavaScript to set it from the email input. Or, if your form has an email field, FormFast automatically sets Reply-To from it.

With JSON submissions

Special fields work the same way with JSON payloads:

JavaScript
await fetch("https://formfa.st/f/your_endpoint_id", {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
    Accept: "application/json",
  },
  body: JSON.stringify({
    name: "Jane",
    email: "jane@example.com",
    message: "Hello!",
    _subject: "New inquiry",
    _replyto: "jane@example.com",
  }),
});

Data cleaning

All special fields (prefixed with _) are stripped from the stored submission data. Your dashboard and webhook payloads will only contain the regular form fields.

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