MIME Type Lookup

What is this for?

A MIME type (now called an Internet media type) is a two-part label like image/png or application/json that tells a server, browser, or library how to interpret a chunk of bytes. It's what goes in HTTP Content-Type headers, what Multipart message parts declare, and what file --mime reports. The IANA registry has thousands of entries; this tool covers roughly 120 you'll actually meet in web work.

When to use it

• Setting Content-Type on an API response and wanting the right one for .docx, .heic, or .webmanifest.
• Configuring an upload field's accept attribute or a S3-bucket allow-list.
• Reading a hex dump or a tcpdump and looking up what application/grpc-web actually is.
• Building a static-file server or CDN config and needing extension-to-mime mapping.
• Settling whether to use text/xml or application/xml (use the latter for new code per RFC 7303).

Common gotchas

• Extension does not equal MIME type. .json usually maps to application/json, but a server can serve it as text/plain and browsers will obey the header. Always set the header explicitly.
• JavaScript is messy. RFC 9239 says text/javascript is the preferred type. application/javascript, application/ecmascript, and others are obsolete but still seen.
• OOXML types are very long. application/vnd.openxmlformats-officedocument.wordprocessingml.document for .docx. Don't try to remember them — copy them.
• application/octet-stream means "I don't know". If you control the type, use a real one — browsers may force-download octet-stream content even when it's renderable.
• Charset matters for text types. Content-Type: text/html; charset=utf-8 — without it, browsers guess and sometimes guess wrong (mojibake).
• Magic-byte sniffing differs from the declared type. Browsers may second-guess Content-Type based on file contents (X-Content-Type-Options: nosniff disables this — set it for security).