API Submissions

If your site is a single-page app (React, Vue, Svelte, etc.) or you want to submit without a full page reload, use JavaScript to POST to your formbuild.io endpoint.

JSON submission

Send a JSON body with Content-Type: application/json. Each key must match a name configured in the form's Form Builder; matching values appear in your Inbox and unknown keys are ignored.

const response = await fetch(
"https://formbuild.io/in/YOUR_FORM_ID",
{
method: "POST",
headers: { "Content-Type": "application/json" },
body: JSON.stringify({
name: "Jane Doe",
email: "jane@example.com",
message: "Hello from my app!",
}),
}
);

if (response.ok) {
// Success — show a thank-you message
} else {
const err = await response.json();
// err.error describes what went wrong
}

Form data submission

You can also send FormData — useful when your JavaScript collects values from an existing form element. Text values are accepted; binary file parts are currently ignored.

const form = document.getElementById("my-form");
const formData = new FormData(form);

const response = await fetch(
"https://formbuild.io/in/YOUR_FORM_ID",
{
method: "POST",
body: formData,
// Do NOT set Content-Type — the browser sets it
// automatically with the correct boundary.
}
);

Preventing duplicate responses

If a user double-clicks submit or the network retries, you can prevent duplicate responses by sending an Idempotency-Key header. Use a unique value per submission attempt (e.g. a UUID generated on the client).

const response = await fetch(
"https://formbuild.io/in/YOUR_FORM_ID",
{
method: "POST",
headers: {
"Content-Type": "application/json",
"Idempotency-Key": crypto.randomUUID(),
},
body: JSON.stringify({ email: "jane@example.com" }),
}
);

If the same key is sent again within 24 hours, we return the original success response without creating a second entry.

Handling errors

The endpoint returns standard HTTP status codes:

CORS

The submission endpoint allows requests from any origin ( Access-Control-Allow-Origin: *), so fetch() from any domain will work without proxy workarounds.

Need to manage forms or read responses?

This page documents the public submission endpoint. To create API keys, manage forms, or read stored responses from a trusted server or AI agent, use the authenticated REST API & API Keys.