Developer & Tech
MIME Type Lookup
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How to use it
Using the mime type lookup
- 01
Type the extension
pdf, PNG, .jpg; case and the dot do not matter.
- 02
Copy the header
Use the suggested Content-Type row directly in your server config or upload handler.
Good to know
Why MIME types matter
Browsers decide whether to render, play, execute or download a response based almost entirely on its Content-Type header. A wrong type breaks image previews, triggers download prompts, or worse; lets an uploaded file be interpreted as HTML, opening XSS holes.
The octet-stream fallback
application/octet-stream means “opaque bytes”: browsers will download rather than display. It is the correct honest answer for anything unrecognized, and safer than guessing a renderable type.
How it's calculated
The math behind this calculator
extension → static MIME map (IANA media types)The extension is trimmed of any leading dot, lowercased and matched against a curated map of roughly forty common media types. Unknown extensions return application/octet-stream with an explicit note instead of pretending to know.
Assumptions & limitations
- Curated common-type table, not the full IANA registry.
- Some formats legitimately carry multiple MIME types (e.g. js).
- Servers may add charset parameters separately.
Worked example
A .pdf file should ship with Content-Type: application/pdf so browsers render it with their built-in viewer instead of downloading it.
FAQ
Frequently asked questions
- Is it js or application/javascript?
- Both appeared historically; current guidance favors text/javascript and modern browsers accept it universally.
- Do I need charset=utf-8 too?
- For text/* responses, yes; append it (e.g. text/html; charset=utf-8) so browsers decode correctly.
- Where is the authoritative list?
- The IANA media types registry at iana.org/assignments/media-types; our table covers the everyday subset.
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