application/*
application/x-www-form-urlencoded
Classic HTML form submission — key=value&key=value pairs.
What is application/x-www-form-urlencoded?
application/x-www-form-urlencoded is the default Content-Type sent by HTML <form method="POST"> submissions. Fields are encoded as key=value pairs joined by ampersands, with special characters percent-encoded.
Typical usage
Traditional HTML form POST, OAuth 2.0 token requests, many legacy APIs.
Common gotchas
Cannot represent binary data or nested structures cleanly. For file uploads use multipart/form-data; for structured payloads use application/json.
HTTP header example
Response header
Content-Type: application/x-www-form-urlencoded; charset=utf-8Reference
HTML Living Standard §4.10.21.7
Frequently asked questions
What is the application/x-www-form-urlencoded MIME type?
application/x-www-form-urlencoded is the default Content-Type sent by HTML <form method="POST"> submissions. Fields are encoded as key=value pairs joined by ampersands, with special characters percent-encoded.
What file extension does application/x-www-form-urlencoded use?
application/x-www-form-urlencoded has no single canonical file extension — it is used as a transfer / content type rather than being tied to a specific file name suffix.
How do I set the Content-Type for application/x-www-form-urlencoded?
Send the HTTP response header Content-Type: application/x-www-form-urlencoded; charset=utf-8. Traditional HTML form POST, OAuth 2.0 token requests, many legacy APIs.
Is application/x-www-form-urlencoded an official MIME type?
Yes. application/x-www-form-urlencoded is officially registered with IANA (HTML Living Standard §4.10.21.7), so standards-conformant clients recognize it.
What are common mistakes with application/x-www-form-urlencoded?
Cannot represent binary data or nested structures cleanly. For file uploads use multipart/form-data; for structured payloads use application/json.