File Extension Lookup
Look up what a file extension means and what opens it.
What is this file?
A file extension — the letters after the dot in a filename — indicates the file's type and what program handles it. This looks up what an extension means and what it is used for, helping you identify an unfamiliar file.
Enter a file extension to look it up.
What the extension does and doesn't tell you
The extension is how your operating system decides which program to open a file with, and knowing what an unfamiliar one means helps you understand what you are dealing with and how to open it. But it is worth understanding an important limitation: the extension is just part of the filename and does not actually determine what the file really is — it can be renamed or wrong, and a file with a misleading extension is a classic trick for disguising something. The true type of a file is defined by its actual contents, not its name, which is why identifying a file by its internal signature is more reliable than trusting the extension. For everyday purposes, though, looking up an unfamiliar extension is a quick way to learn what kind of file you have and what can open it, which is usually all you need to know.
Common questions
What does a file extension tell me?
The file's likely type and what program opens it — the operating system uses it to decide which application to launch.
Can a file extension be wrong?
Yes — it is just part of the name and can be renamed or misleading. The file's true type is defined by its contents, which its internal signature reveals more reliably.
Is anything uploaded?
No. The lookup happens in your browser.