Find Any File Extension, Open It and Fix It
WhatIsFileExtension is a free file extension lookup with 96 file types explained step by step. Search any extension to see what it is, then open, check, fix or convert the file.
We do not have that extension yet. Submit it as a new file type and our team will research it.
What Is a File Extension and Why Does It Matter?
Four quick facts that answer most questions before you search.
What the letters mean
A file extension is the code after the last dot, like .eml or .dwg. Your computer reads it to choose the app that opens the file.
How to see it
Windows File Explorer shows extensions under View, then File name extensions. Mac Finder shows them under Settings, then Advanced.
Why a file fails
The app is missing, the file is damaged or the extension does not match the data. Every guide lists the checks in that order.
When to be careful
Program types like .exe and .msi can start code on your computer. Look an unknown extension up before you open the file.
How can WhatIsFileExtension Help You?
Guides Built on Our Own Test Files
How We Test Every Guide
Collect the files
We build sample files or collect public ones, then add copies we damage on purpose.
Open them in the readers
Every copy goes into the apps people use, and we note what loads and what fails.
Publish what we saw
Every guide reports the counts, the fixes that worked and the cases that stay unsolved.
55 Damaged LDIF Files, Two Readers and 7 Silent Misses
We wrote one LDIF file, damaged it in 55 ways and loaded every copy into two readers. On 7 copies both readers loaded wrong data and printed no message.
Read the LDIF studyOne square is one damaged copy
Latest Fix Guides From Our Tutorials
Expert insight
Most file problems start with one question. What is this extension and which app reads it? We test every guide on our own files and damaged copies, so you get the result we saw and not a guess.
File Extension List: Browse All 96 File Types
Blue chips with a green mark have a tested guide. Gray chips lead to a file type page.
Email, Contacts and Calendars
Databases and Data Files
Backups, Disks and Images
Documents and Books
Images, Video, Audio and Drawings
Programs, Code and System Files
Archives, Protected and Other Types
File Extension Questions Answered
What is a file extension?
A file extension is the short code after the last dot in a file name, like .docx or .jpg. Your computer reads it to choose the app that opens the file. The same letters also show what kind of data is inside.
What is the difference between a file extension and a file format?
The extension is the label at the end of the name. The format is the way the data is arranged inside the file. One format can use more than one extension, and two different formats can share the same one.
Can you rename a file to convert it?
No. Renaming changes the label and leaves the data as it was, so apps cannot read the file. Open the file in an app that supports it and export a new copy, or use a converter built for that format.
How do you find out what a file extension is?
Type the extension in the search box at the top, or browse the file extension list below. Every page names the format, the apps that open it and the checks we completed.
What if your extension is not in the library?
Send it through the Submit a File Type page. Our team researches the format, tests it on our own files and adds a guide.
Is WhatIsFileExtension free to use?
Yes. Every guide in the library is free to read and needs no sign up. The Software Store lists paid tools for jobs that a manual step cannot finish.
Submit a File Type
Missing an extension? Send it to our team and we will research it, test it on our own files and add a guide.