Glossary · Internet & Web

MIME Type (Media Type)

A MIME type is a label such as text/html or image/png that tells a browser what kind of data a response contains and how to handle it.

Updated October 6, 2026

A MIME type, or media type, is a standard identifier for the format of a file or response, written as type/subtype. Servers send it in the Content-Type header so clients know how to interpret the body.

Why it matters

A wrong type can break a site: a stylesheet served as text/plain may be ignored, and JSON served as HTML can be mis-rendered. Browsers may also guess types, which is a security risk, so the X-Content-Type-Options: nosniff header tells them to trust the declared type.

You can see the declared type for any URL by inspecting its response headers, which is the fastest way to confirm whether a server migration changed how files are labeled.

Example

Content-Type: text/html; charset=utf-8
Content-Type: application/json
Content-Type: image/webp

Common mistakes

  • Serving JavaScript or CSS with an incorrect type after a server migration.
  • Omitting the charset for text responses.
  • Relying on file extensions instead of sending the header correctly.

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