Web & Networking › API Styles & Formats

Request and Response Body

The payload sent with a request or returned in a response, usually JSON.

Also known as: request body, response body, payload, HTTP body

The body is the data part of an HTTP message: what you’re actually sending or receiving. The headers and URL describe and address it; the body is the content.

POST /orders HTTP/1.1
Content-Type: application/json

{"item_id": 7, "quantity": 2}

HTTP/1.1 201 Created
Content-Type: application/json

{"id": 917, "item_id": 7, "quantity": 2, "status": "pending"}

The first is the request body: what the client sends. The second is the response body: what the server returns.

Which requests have one

Use the URL’s path and query to say what you want; use the body to carry the data.

The format must match the header

Content-Type tells the receiver how to read the body: application/json, multipart/form-data for file uploads (multipart) or application/x-www-form-urlencoded for classic HTML forms. If the header and the body don’t match, the server will usually reject or mis-parse it.

await fetch("/orders", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({ item_id: 7, quantity: 2 }),
});

Good practice

• Validate incoming bodies: never trust the shape or types.
• Return a consistent error body with a clear message when a request fails (with the right status code).
• Keep bodies reasonable in size, and paginate big lists.
• Don’t log full bodies that may contain passwords or personal data.
• Reading a response body in a browser consumes it once (res.json()), so don’t read it twice.