400 400 Bad Request

When you'll see it

When the server can't read the request or refuses it as invalid: malformed JSON, a missing required field, an invalid header or cookie, or a URL with bad characters.

What to check

• The response body, as many APIs say exactly which field is wrong.
• That the Content-Type matches the body you send, for example JSON sent as application/json.
• In a browser, try clearing the site's cookies. An oversized or corrupt cookie is a common cause.
• That values in the URL are properly encoded.

Example response

HTTP/1.1 400 Bad Request
Content-Type: application/json

{"error": "email is not a valid address"}

SEO impact

If a crawlable URL returns 400, Google will eventually drop it from the index. Fix the underlying issue.

At a glance