How does the tool know which direction I want?

If your input contains a slash it is treated as a MIME type (for example application/json) and the tool returns the associated extensions. Otherwise it is treated as a file extension — with or without a leading dot — and the tool returns the matching MIME type.

Is the lookup done online?

No. The registry is bundled into the page, so every lookup is instant and works offline. Nothing is sent over the network and no input is logged.

Which MIME type should I use for JavaScript?

For files served to browsers, text/javascript is now the standard registered type for .js and .mjs, though application/javascript still works and is widely seen. The tool notes this where relevant.

Why does serving the right Content-Type matter?

Browsers may MIME-sniff a response and, for security, refuse to run a script or apply a stylesheet that is served with the wrong type. Sending the correct Content-Type header prevents broken pages and blocks a class of content-confusion attacks.

What if my extension is not in the registry?

The tool covers the common web, document, image, audio, video, font and archive types. For an unknown binary file, application/octet-stream is the safe default — it tells the browser to download rather than try to render the file.

MIME Type Lookup & File Extension Map

The MIME Type Lookup & File Extension Map answers both questions developers ask about content types: “what MIME type does this extension use?” and “what extensions does this MIME type cover?” It searches a built-in registry instantly and entirely offline.

How it works

The tool ships with a curated subset of the IANA / mime-db registry mapping each MIME type to its associated file extensions. When you type:

an input containing a slash (e.g. application/pdf) it is treated as a MIME type and the tool lists every registered extension;
otherwise the input is treated as a file extension (a leading dot is optional) and the tool returns the matching MIME type along with that type’s full extension list.

If an exact match is not found, the tool falls back to a substring search so a partial MIME fragment still surfaces likely candidates.

Example

Entering png returns image/png with the extension .png. Entering image/jpeg returns the extensions .jpg, .jpeg and .jpe. Entering an unknown extension suggests application/octet-stream as the safe default.

Notes

Use the result to set an accurate Content-Type header on your server. Browsers MIME-sniff responses and, as a security measure, will refuse to execute a script or apply a stylesheet labelled with the wrong type — so correct content types keep pages working and close content-confusion attack vectors. The registry is bundled locally, so lookups need no network access.