Is a file extension the same as a file type?

Not exactly. The extension is the part of the name after the last dot and is just a hint to the operating system. The true file type is determined by the file's actual contents, which is why renaming an extension does not convert the file.

What is the difference between .jpg and .png?

JPG uses lossy compression that is ideal for photographs and small file sizes but discards some detail. PNG uses lossless compression, supports transparency, and is better for logos, screenshots and graphics with sharp edges.

Is anything I search sent to a server?

No. The full list and the search both run entirely in your browser — nothing you type is uploaded anywhere.

Why can't I open a file even though it has a familiar extension?

An extension only tells the OS which program to try. If the file is corrupt, encrypted, or actually a different format with a renamed extension, the matching program may still fail to open it. Renaming an extension never converts the underlying data.

How do I open an unknown file extension safely?

Look up the extension here to identify the likely format and the program that handles it. Be cautious with executable types (.exe, .bat, .sh) from untrusted sources, since opening them runs code.

What is the difference between .zip and .tar.gz?

Both bundle multiple files into one archive. .zip compresses each file individually and is native on Windows and macOS. .tar.gz first tars files into one stream and then gzip-compresses the whole thing, which is common on Linux and often gives slightly better compression.

File Extensions Reference

File extensions — searchable reference

A file extension is the short suffix after the last dot in a filename — like .pdf or .mp4 — that tells your operating system which program should try to open it. This reference is a grouped, searchable list of common extensions across documents, images, audio and video, archives, code and system files, each with a plain-English description so you can identify an unfamiliar file at a glance.

How it works

The tool holds a built-in catalogue of extensions organised into categories. You can browse a whole category, or type into the search box — with or without the leading dot — to filter by the extension itself or by words in its description. The list and search both run instantly in your browser; nothing you type is sent anywhere. Remember that the extension is only a label: the real format is determined by a file’s contents, which is why renaming .png to .jpg does not actually convert the image.

Example

Searching for mp surfaces media formats; searching doc surfaces document formats. A few common entries:

Extension	Category	What it is
.pdf	Documents	Portable Document Format, fixed-layout document
.png	Images	Lossless raster image with transparency
.mp3	Audio	Lossy compressed audio
.mp4	Video	Compressed video container (H.264/H.265)
.zip	Archives	Compressed archive of multiple files
.json	Code	Human-readable structured data

Everything runs in your browser — nothing is uploaded.