MIME Types CheatSheet

MIME stands for Multipurpose Internet Mail Extensions.

A MIME type is a label used to identify a type of data. It is used so software can know how to handle the data. It serves the same purpose on the Internet that file extensions do on Microsoft Windows.

So if a server says "This is text/html" the client can go "Ah, this is an HTML document, I can render that internally", while if the server says "This is application/pdf" the client can go "Ah, I need to launch the FoxIt PDF Reader plugin that the user has installed and that has registered itself as the application/pdf handler."

So if a server says "This is text/html" the client can go "Ah, this is an HTML document, I can render that internally", while if the server says "This is application/pdf" the client can go "Ah, I need to launch the FoxIt PDF Reader plugin that the user has installed and that has registered itself as the application/pdf handler."

Two primary MIME types are important for the role of default types:

• text/plain is the default value for textual files. A textual file should be human-readable and must not contain binary data.
• application/octet-stream is the default value for all other cases. An unknown file type should use this type. Browsers pay a particular care when manipulating these files, to protect users from software vulnerabilities and possible dangerous behavior.

If the web server or application reports an incorrect MIME type for content, a web browser has no way, according to the HTTP specification, of knowing that the author actually intended the content to be processed and displayed in a way different from that implied by the reported MIME type.

Some other web browsers, such as Internet Explorer, try to allow for misconfigured web servers and applications by guessing what the correct MIME type should be. This has sheltered many web administrators from their own errors as, using this method, Internet Explorer will continue to process content as expected even though the web server is misconfigured, e.g., it may correctly display an image that is reported to be plain text.

Serving content using the correct MIME type can also be important for security reasons; its possible for malicious content to affect the users computer by pretending to be a safe type of document when it is in fact not.

There are several steps you can take to determine the correct MIME type value to be used for your content:

1. If your content was created using a vendors software application, read the vendors documentation to see which MIME types should be reported for its media types.
2. Look in the IANA/MIME Media Types registry, which contains all registered MIME types.
3. Search for the file extension at FILExt or File extensions reference to see what MIME types are associated with that extension.