Do I need to include the dot?

No. You can type png or .png — the lookup strips a leading dot automatically. Search is case-insensitive, so PNG and png both work.

A MIME (or media) type is a standardized label like image/png that tells software and servers what kind of data a file holds. Web servers send it in the Content-Type header so browsers know how to handle the response.

Why might one extension have several meanings?

Some extensions are reused by unrelated formats. For example .dat is generic and used by many programs. When that happens the entry notes the most common interpretation and that the format may vary.

Can the extension be trusted to identify a file?

Not always. Extensions are just hints and can be renamed. For certainty, inspect the file's magic-number signature or its actual MIME type rather than relying on the extension alone.

Does this run offline?

Yes. The extension database ships with the page and all searching happens in your browser, so no data is sent anywhere and it works without a connection.

File Extension Lookup

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File extension lookup

A file extension is the short suffix after the last dot in a filename, like .png or .docx. It hints at the file’s format and which application should open it, and it usually maps to a standard MIME content-type used on the web. This tool lets you search a curated database of common extensions and instantly see the format name, MIME type, category, and the programs that typically handle the file.

How it works

The lookup normalizes your input — stripping a leading dot and lowercasing — then matches it against the extension database. Each record carries a human-readable format name, a canonical MIME type (for example application/pdf), a category (image, document, archive, audio, code, and so on), and a list of common applications. You can also filter the whole list by category to browse families of formats. All matching happens locally.

Tips and notes

Extensions are hints, not guarantees — a file can be renamed. For trustworthy detection, check the file’s binary signature (magic numbers) or its server-reported Content-Type.
Generic extensions like .dat or .bin have no single format; the entry flags these as ambiguous.
Web servers should send the listed MIME type so browsers render or download the file correctly — see the related Content-Type lookup for the reverse mapping.