File Extension Lookup
Search 507 file extensions by extension, MIME type, description or category and see the format name, popularity, and which apps open it on Windows, macOS and Linux.
Input
Search by extension (.pdf), MIME type (application/pdf), description (video), or category (Audio). Leave blank to browse them all.
Output
| Extension | Category | Popularity | MIME type | Description | Opens with |
|---|---|---|---|---|---|
| No data yet | |||||
Guides
File Extension Lookup is a searchable reference for 507 common and rare file
extensions. Type an extension, a MIME type, or a keyword and instantly see what
the format is, how common it is, its official MIME type, and which applications
open it on Windows, macOS, and Linux. It's the fastest way to answer "what is a
.heic file?" or "which program opens a .dwg?" without wading through search
results.
How to use it
- Type in the Search box. You can enter an extension (with or without the
leading dot, e.g.
.pdforpdf), a MIME type (application/pdf), a description keyword (video), or a category name (Audio). - Use Search in to narrow the match to a single field — Extension only, MIME type only, or Category only — or leave it on All fields to match any of them.
- Use Popularity to show everything, only everyday Common formats, or only Rare and specialist ones.
- Leave the search box empty to browse the whole catalogue.
Results appear in a table with the extension, category, popularity, MIME type, a plain-English description, and the apps that open it per platform. Use the copy and download buttons to export the current results as CSV.
Why does the same MIME type appear for several extensions?
MIME types describe a content type, not a single file name. Formats such as
.md, .markdown, and .mkd all resolve to text/markdown, and many archive
or image variants share a base type. The extension is what the operating system
actually keys file associations on.
What's the difference between "Common" and "Rare"?
Common extensions are ones most people encounter — documents, images, audio, video, and mainstream code and config files. Rare covers niche, legacy, or specialist formats you'll only meet in a specific tool or industry. The popularity filter lets you hide the long tail when you just want the everyday answer.
The extension I typed isn't listed — is it invalid?
Not necessarily. The catalogue focuses on 507 widely-used and notable formats, so very obscure, proprietary, or made-up extensions may not appear. An extension is just the text after the last dot in a file name; any program can define its own.
Is a file's extension a guarantee of its contents?
No. Extensions are a naming convention, not a security boundary — a file can be renamed to any extension regardless of what's inside it. Treat the extension and MIME type as a strong hint, and verify the actual bytes (a "magic number" / file signature check) when authenticity matters.
Privacy
This lookup runs entirely in your browser against a built-in dataset. Nothing you type in the search box is uploaded, logged, or sent to any server — the whole extension database ships with the page, so searches are instant and completely private.