Diagnose Netlify Forms: not detected, submissions missing, or 404 on submit

TL;DR

Use Netlify's own reCAPTCHA integration (data-netlify-recaptcha="true" plus the recaptcha div) instead of a parallel custom flow. There are three distinct failure modes with different fixes, so classify first: (A) the form was never registered (detection), (B) the form is registered but submissions don't appear, (C) submissions return 404.

When to use

You are seeing this: Form detection runs during post-processing of each deploy: Netlify scans the built, published HTML for <form> elements carrying data-netlify="true" or the bare netlify attribute, and registers each one under its name attribute. Use this skill when you run into "Diagnose Netlify Forms: not detected, submissions missing, or 404 on submit".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Use this when a Netlify-handled form doesn't work. There are three distinct failure modes with different fixes, so classify first: (A) the form was never registered (detection), (B) the form is registered but submissions don't appear, (C) submissions return 404.

1. Is the form registered at all?

Form detection runs during post-processing of each deploy: Netlify scans the built, published HTML for <form> elements carrying data-netlify="true" or the bare netlify attribute, and registers each one under its name attribute. Check the site's Forms tab in the Netlify UI for your form's name.

• Name absent → failure mode A (detection). Go to section 2.
• Name present → failure mode B or C. Go to section 3.

2. Mode A: the form was never detected

Causes, in likelihood order:

1. The form isn't in the built HTML. Detection only sees the static HTML produced at build time. If the form is rendered client-side (React, Vue, Next.js, Astro, SvelteKit), the parser never sees it. Fix: add a static skeleton file in the publish directory (conventionally public/__forms.html) containing a hidden copy of every form, with exactly the same name, field names, and honeypot field:

<form name="contact" data-netlify="true" netlify-honeypot="bot-field" hidden>
  <input type="hidden" name="form-name" value="contact" />
  <input type="text" name="name" />
  <input type="email" name="email" />
  <textarea name="message"></textarea>
  <input name="bot-field" />
</form>

The hidden attribute keeps it invisible; the file must ship in the publish directory. One skeleton file can hold all of your forms.

2. Missing or mismatched attributes. The form needs data-netlify="true" (or bare netlify) and a name attribute. On AJAX posts, the request body must also carry a hidden input whose name is form-name and whose value exactly equals the form's name:

<form name="contact" method="POST" data-netlify="true">
  <input type="hidden" name="form-name" value="contact" />
  [!-- ... fields ... --]
</form>

3. Detection was off, or the fix hasn't been deployed. Form detection must be enabled in site settings, and every markup fix needs a new deploy detection only runs on the latest deploy's HTML.

After redeploying, confirm the form name appears in the Forms tab before testing again. Submissions made before registration are lost.

3. Mode B: the form is registered, but submissions are missing

1. Check the spam tab first. Netlify filters submissions through Akismet. Legitimate-looking test submissions get flagged constantly: sending from a throwaway address, one-line messages, or rapid-fire tests from one IP are classic spam signals. Test with a real email address and a realistic message, then look in the Spam list and mark it verified.

2. Check the form-name hidden input on AJAX submissions. Without <input type="hidden" name="form-name" value="[exact form name]"> in the POST body, Netlify can't route the submission and it silently fails.

3. Check field names against the registered form. Netlify validates submitted field names against the registered form definition, a renamed input in your component won't appear where you expect. (The UI shows only the fields from the last deployed form version; old submissions keep their data but won't show the new fields. Mark fields hidden instead of deleting them if you need continuity.)

4. Don't hand-roll reCAPTCHA next to Netlify's. If you're doing custom reCAPTCHA verification inside your own function and POSTing to the form endpoint yourself, Netlify's form processing may never run. Use Netlify's own reCAPTCHA integration (data-netlify-recaptcha="true" plus the recaptcha div) instead of a parallel custom flow.

4. Mode C: 404 on submit

POSTing to a form name that isn't registered returns 404, and so does posting after the form was deleted (deletion is permanent; export a CSV first). Fix: go back to section 2, register the form, redeploy, and confirm it before resubmitting. For AJAX, POST to / (or the page's own path) with Content-Type: application/x-www-form-urlencoded.

5. Checklist

1. Forms tab: is the name listed? No → detection problem (built HTML, skeleton file, attributes, redeploy).

2. Listed but nothing arrives → spam tab (Akismet), then the form-name hidden input, then field-name match.

3. 404 → the form was deleted or never registered; register and redeploy.

4. Every markup fix requires a new deploy, detection only sees the latest build's HTML.

5. Test with a real email and realistic content, not throwaway one-liners.

Built from Netlify's Forms docs pattern as implemented in netlify/context-and-tools and community preflight guides (form detection scans built HTML at deploy time for data-netlify/netlify attributes; form-name hidden input must match the form name; Akismet spam filtering flags test submissions) and recurring answers.netlify.com threads on forms not detected and submissions not appearing.