How to use it
- Type an extension such as pdf or .png into Extension or media type, or type a full type such as image/jpeg.
- Read Media type and Extensions. When one extension belongs to several types, the Matching types table lists them all.
- Check Registration to see whether the type is in the IANA registry, and which reference registered it.
Extensions and media types
A file extension is the part of a file name after its last dot. A media type, also called a MIME type, names what the content of a file is, in the form type/subtype, such as application/pdf or image/png. Email, web servers and browsers use the media type in the Content-Type header, and programs use the extension to choose which application opens a file.
RFC 6838 section 4.2 sets the rules for type and subtype names. The extension is only a naming convention, so a file can carry any extension.
Registered and unregistered types
The IANA registry is the official list of media types. RFC 6838 gives four trees for names: the standards tree, with no prefix (section 3.1); the vendor tree, with the prefix vnd. (section 3.2); the personal tree, with prs. (section 3.3); and the unregistered tree, with x. (section 3.4). Many types in use, especially vendor types, are not in the registry at all, and the page says so.
Where the extensions come from
The IANA registry does not list extensions, so the extensions come from the Apache httpd mime.types file. It is a long-used list of common types and their extensions, and its header places it in the public domain. The file does not cover every type: text/markdown, for example, has no extension in it. One extension can belong to two types, such as sub, which the file lists for image/vnd.dvb.subtitle and for text/vnd.dvb.subtitle; the page then shows both rows, and the program that opens the file decides which one applies.
Worked example: pdf
Typing pdf finds one type, application/pdf. The Apache file lists the extension pdf for it, and the IANA registry has the type, registered by RFC 8118.
The table below is what the page shows for pdf, and the same result comes from typing .PDF or application/pdf.
| Output | For pdf |
|---|---|
| Media type | application/pdf |
| Extensions | |
| Registration | Registered with IANA: RFC 8118 |
Frequently asked questions
Is a MIME type the same as a media type?
Yes. Both names mean the type/subtype label of content, such as image/png. RFC 6838 calls it a media type, and the older name MIME type is still used in many programs and documents.
Why does jpg give image/jpeg and not image/jpg?
image/jpeg is the type. The Apache file lists three extensions for it: jpeg, jpg and jpe. Neither the IANA registry nor the Apache file has an image/jpg type, so the page does not show one.
Why does a type show no extensions?
The Apache file lists common extensions only. A type can be in the IANA registry and still have no extension in that file, such as text/markdown, and then the page says that no extension is listed.
Can one extension belong to two media types?
Yes. The Apache file lists sub for both image/vnd.dvb.subtitle and text/vnd.dvb.subtitle, so the page shows both. The program that opens the file decides which type it uses.
Can I tell the type of a file from its extension alone?
Only roughly. The extension is a naming convention, and a file can be renamed to any extension. For a security check, look at the content of the file, not only its name.
Is my search sent anywhere?
No. The lookup runs in your browser against the list stored with the page, and nothing you type is sent to our server or stored there.
Sources
- IANA Media Types registry
- RFC 6838: Media Type Specifications and Registration Procedures
- Apache httpd docs/conf/mime.types (extension mapping, public domain)
Figures and text last checked on Tuesday, November 10, 2026.