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This site simply hosts icons for lots of filetypes that you can use and link to. You can use a file extention like /html, a filename like /movie.avi, a mimetype like /application/pdf and/or choose from a specific set like /neu/html or even combine them like /neu/image/png. You can also use the ?size=16 to get a consistent size of icons, and the ?default=... to force a default instead of an HTTP 404.

Conversions

File extension to mimetype lookup like /extension/html or /extension/codemonkey.mp3 or in JSONP /extension/txt?callback=cb

Mimetype to file extension like /mimetype/application/postscript or /mimetype/application/zip

Or the whole dump in json or xml (from python mimetypes and apache)