“TypeError: Body is unusable: Body has already been read” in Next.js and Node

What we saw

On 16.10.2026 we wrote a Next.js 16.4.2 route that reads await request.json(), logs a field, and then reads request.json() again, the way a logging helper or a validation library might. The first read worked. The second threw TypeError: Body is unusable: Body has already been read, and the route answered 500 with an empty body. In the browser that empty 500 then broke response.json() with “Unexpected end of JSON input”, so the visitor's side shows a different error from the server's.

The same mistake on a response in the browser gave a different message in each engine:

We check the Workers row with a test in this site's own code: it reads a body twice in the Workers runtime and compares the error with the row.

Why a body can be read only once

A request or response body is a stream. json(), text(), formData() and arrayBuffer() each read the stream to the end, and after that nothing is left to read. It often happens without a second json() in sight: middleware or an auth helper reads the body first, a console.log(await response.text()) added for debugging sits above the real json(), or a retry reuses the same Response.

Read once, or clone first

Keep the parsed body in a variable and pass it to whatever needs it. If two parts of the code really need the raw stream, call clone() before the first read and give each reader its own copy. The tee() in the Cloudflare message splits the body stream in two, and clone() calls it for you.

export async function POST(request) {
  const body = await request.json(); // read once
  await logRequest(body);            // pass the parsed value on
  await saveMessage(body);
  return Response.json({ ok: true });
}

// If two places really need the raw body, clone before the first read:
// const copy = request.clone(); const forLog = await copy.text();

If the route only forwards a contact form

A route that exists only to pass form fields on to email can be dropped: the form can post straight to Formgong at https://formgong.com/submit, and there is no body of yours to read twice. See the HTML guide.