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.

What is the File Extensions Reference?

A searchable file extensions reference grouped by documents, images, audio and video, archives, code and system files — each with a plain-English description. Runs entirely in your browser, nothing is uploaded. It runs free in your browser on Gera Tools, with nothing uploaded.

File Extensions Reference

Name: File Extensions Reference
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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.

Extensions by category — a quick-reference table

Documents and data

Extension	What it is
.pdf	Portable Document Format — fixed layout, widely supported
.docx	Microsoft Word document (Open XML format)
.xlsx	Microsoft Excel spreadsheet (Open XML format)
.csv	Plain-text table with comma-separated values
.json	Lightweight structured data; human-readable key-value pairs
.xml	Markup language for structured hierarchical data
.md / .markdown	Plain text with lightweight Markdown formatting

Images

Extension	What it is
.jpg / .jpeg	Lossy compressed photo — small files, some quality loss
.png	Lossless raster image with optional transparency
.gif	Lossless 256-colour image; supports animation
.webp	Modern lossy/lossless format; smaller than PNG or JPEG
.svg	Scalable Vector Graphics — XML-based, resolution-independent
.heic	Apple’s High Efficiency Image format used on iPhones
.raw	Unprocessed camera sensor data (varies by manufacturer)

Audio and video

Extension	What it is
.mp3	Lossy compressed audio; universal compatibility
.flac	Lossless audio; full quality, larger files
.aac	Compressed audio used in AAC/M4A files and streaming
.wav	Uncompressed PCM audio
.mp4	Video container typically with H.264 video and AAC audio
.mkv	Matroska container; supports many codecs and subtitle tracks
.mov	Apple QuickTime movie format

Extension	What it is
.zip	Compressed archive, native on Windows and macOS
.tar.gz / .tgz	Tarball then gzip-compressed; common on Linux
.7z	7-Zip archive with stronger compression than ZIP
.rar	Proprietary compressed archive

Code and system files

Extension	What it is
.js	JavaScript source file
.ts	TypeScript source file
.py	Python script
.sh	Bash or POSIX shell script
.exe	Windows executable — runs code when opened
.dll	Windows Dynamic Link Library — not run directly
.dmg	macOS disk image for application installers
.iso	Optical disk image — CD/DVD/Blu-ray replica

Common misunderstandings

Renaming an extension never converts a file. Changing .png to .jpg makes your OS try to open it as a JPEG, but the underlying bytes are unchanged. You need an actual conversion tool to change the format.

An extension is just a hint. A malicious file can be disguised with a harmless-looking extension. Be cautious opening unknown file types, especially executables (.exe, .bat, .sh, .vbs), from untrusted sources — they run code when opened.

Why can’t I open this? If a familiar extension fails to open, the file may be corrupt, incomplete (a partial download), or protected with encryption. The extension tells you which program to try; it cannot tell you whether the file is intact.

Everything runs in your browser — nothing is uploaded.