Identify a file extension
What is a file extension lookup tool?
A file extension is the group of characters after the final period in a filename, such as .pdf, .zip or .exe. It helps the operating system and applications identify the expected file format, but an extension alone does not prove that a file is genuine or safe.
This lookup provides plain-language descriptions, common programs and security guidance for frequently encountered file types. It works locally in your browser and does not inspect or upload the file itself.
Understand the format
Learn whether a file is a document, archive, image, executable, system file or another type.
Choose an application
See common software categories that can open or extract the format.
Review security risk
Recognize executable, script and archive formats that deserve additional caution.
How to check an unknown file safely
- Display full filename extensions in Windows before trusting the visible name.
- Confirm the sender, download source and expected file type.
- Scan unexpected downloads with updated security software.
- Do not enable macros or run executable files unless the source and purpose are verified.
Safety note: This utility provides educational troubleshooting guidance. Back up important data before system changes and use qualified support when hardware damage, data loss or electrical risk is possible.
Common file-extension categories
Related TipsMake utility tools
Frequently Asked Questions
Can I make a file work by changing its extension?
Usually no. Renaming changes the label, not the internal format, and can make the file harder to identify.
Which file types deserve extra caution?
Executables, installers, scripts, macro-enabled Office files, registry files and unknown archives deserve extra caution.
Why are file extensions sometimes hidden?
Windows can hide known extensions by default. Showing extensions helps reveal misleading names such as invoice.pdf.exe.