File Extension Lookup
Identify files across a broad standards-backed index, with detailed opening guidance for hundreds of common and specialist formats.
What Is the File Extension Lookup?
The File Extension Lookup combines 330 curated, richly explained formats across 20 industries with a bundled standards-backed MIME index containing 1,246 unique extension associations. Curated entries retain specific opening guidance, while the larger index adds broad coverage of registered document, media, archive, code, scientific and application formats. Search by extension, name, category, application guidance or MIME type.
How It Works
Type an extension (with or without the dot), a format name, an app name, or tap a category chip. Results filter instantly; use Show All to expand past the first 40.
When to Use It
Use it when someone sends an unfamiliar file, when deciding whether an attachment is safe to open, when moving work between industry tools, or when picking an export format.
Frequently Asked Questions
- Is The Extension Always The Truth?
- No — an extension is just part of the name. Verify the real format from the file's bytes with the File MIME Type Checker.
- Why Do Some Extensions Appear Twice?
- A few genuinely mean different things in different fields — .vcf is a contact card in email and a variant call file in genomics, for example.
- Does This Include Every File Extension?
- No universal master list exists because any application or organization can create a private extension. The lookup merges 330 curated specialist entries with 1,246 MIME associations from an index sourced from Apache, NGINX and IANA, producing about 1,385 distinct extensions after overlaps are removed.
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