What does that file extension mean?
Paste a filename — even a tricky one like archive.tar.gz or .gitignore — and instantly see its file type, purpose, common software, and safety guidance.
File extension lookup
Browse popular file extensions
Jump straight to a detailed reference page for a specific format:
Frequently asked questions
Is it safe to trust a file just because of its extension?
No. An extension is just text the file's creator chose to put after the last dot in its name — it's not verified or enforced by anything. A file can be renamed to any extension regardless of its real content. Use antivirus scanning and your judgment about the source, not the extension, to assess safety.
How does this tool handle something like archive.tar.gz?
It recognizes known "compound" extensions such as .tar.gz, .tar.bz2, and .tar.xz as a single unit rather than only looking at the final ".gz" — so you get accurate information about the combined format instead of a partial answer.
What about filenames with lots of dots, like report.v2.final.docx?
Only extension combinations we specifically recognize (like .tar.gz) are treated as compound. Anything else falls back to the very last segment after the final dot, so report.v2.final.docx is correctly read as a .docx file, not ".final.docx".
What happens with hidden files like .gitignore or .env?
Files that start with a dot and have no other dot (like .gitignore) are recognized as "dotfiles" in their own right, since the whole name is their identity rather than a base name plus extension. Hidden files that do have a real extension, like .eslintrc.json, are still analyzed by that extension and flagged as hidden.
What if my file has no extension at all, like Makefile or README?
We check the exact filename against a list of well-known extensionless conventions (Makefile, Dockerfile, README, LICENSE, and similar). If it's not on that list, we say so plainly rather than guessing — a name with no extension genuinely carries no format information.
What if my extension isn't in your database?
You'll get a clear fallback explaining that the extension isn't recognized yet, along with a close-match suggestion if your input looks like a likely typo of a known extension. An unrecognized extension isn't inherently suspicious — it may just be rare or new.
Does this tool upload my filename anywhere?
No. Everything — parsing the filename and looking up its extension — runs entirely in your browser using a bundled, static dataset. Nothing is sent to a server, logged, or stored.