If file names are like book titles, then file extensions are the genre tags. They tell your computer what kind of file it’s dealing with and what program should open it.
That little dot-something at the end of a file—like .docx or .jpg—isn’t just decoration. It can mean the difference between opening a vacation photo or launching a malicious program that eats your hard drive for breakfast.
Let’s break down 50 common (and sometimes sneaky) file extensions, from everyday documents to files that deserve side-eye.
🔤 50 File Extensions (Alphabetical, for Your Sanity)
.apk – Android App Package
📱 For: Android apps
📍 Where: Mobile downloads, app stores
🛠️ Open with: Android device, emulators
⚠️ Can be risky if downloaded from shady sources.
.bat – Batch File
🧮 For: Running scripts in Windows
📍 Where: System automation tasks
🛠️ Open with: Notepad (to view), Windows (to run)
⚠️ May contain commands that can mess up your system—don’t run unless you trust the source!
.csv – Comma-Separated Values
📊 For: Spreadsheet data
📍 Where: Financial or database exports
🛠️ Open with: Excel, Google Sheets, Notepad
.dll – Dynamic Link Library
🧩 For: Windows system functionality
📍 Where: Program files
🛠️ Open with: You don’t—just leave them alone!
⚠️ Critical system files—don’t delete or open randomly.
.doc / .docx – Microsoft Word Document
📝 For: Text documents
📍 Where: Resumes, letters, articles
🛠️ Open with: Word, Google Docs, LibreOffice Writer
.exe – Executable File
🖥️ For: Running programs on Windows
📍 Where: Software installers
🛠️ Open with: Windows
⚠️ Can be dangerous—NEVER open an .exe file from an unknown sender.
.flac – Free Lossless Audio Codec
🎵 For: High-quality music
📍 Where: Music libraries, audio editing
🛠️ Open with: VLC, Foobar2000
.gif – Graphics Interchange Format
🖼️ For: Animations or short looping images
📍 Where: Memes, websites
🛠️ Open with: Any browser, image viewer
.html / .htm – HyperText Markup Language
🌐 For: Web pages
📍 Where: Saved websites
🛠️ Open with: Browser (Chrome, Firefox)
.ics – Calendar File
📅 For: Event invites
📍 Where: Email attachments
🛠️ Open with: Google Calendar, Outlook
.iso – Disk Image
💿 For: Virtual copies of CDs/DVDs
📍 Where: Software downloads
🛠️ Open with: Disk mounting tools, Windows 10+
⚠️ Use only from trusted sources.
.jar – Java Archive
☕ For: Java programs
📍 Where: Games, software
🛠️ Open with: Java Runtime Environment
⚠️ Can be risky if from unknown sources.
.jpeg / .jpg – Compressed Image
📷 For: Photos
📍 Where: Cameras, phones, websites
🛠️ Open with: Image viewer, Paint, Photoshop
.js – JavaScript
🔧 For: Website functionality
📍 Where: Web development folders
🛠️ Open with: Code editors
⚠️ Can run code—don’t click random .js files.
.json – JavaScript Object Notation
📋 For: Data exchange
📍 Where: App settings, web data
🛠️ Open with: Notepad, VS Code
.lnk – Windows Shortcut
🧭 For: Shortcuts to files
📍 Where: Desktop icons
🛠️ Open with: Automatically by Windows
⚠️ Make sure it’s pointing somewhere safe!
.log – Log File
🧾 For: Program status reports
📍 Where: App folders
🛠️ Open with: Notepad
.m4a – Audio File
🎧 For: Music/audio
📍 Where: iTunes, phone recordings
🛠️ Open with: iTunes, VLC
.mov – Apple QuickTime Movie
🎬 For: Videos
📍 Where: Mac devices, cameras
🛠️ Open with: QuickTime, VLC
.mp3 – Audio File
🎶 For: Music
📍 Where: Music libraries
🛠️ Open with: Any music player
.mp4 – Video File
📽️ For: Most video content
📍 Where: Everywhere!
🛠️ Open with: VLC, Windows Media Player
.odt – OpenDocument Text
📝 For: Documents from LibreOffice
📍 Where: LibreOffice users
🛠️ Open with: LibreOffice Writer, Word
.ogg – Audio File
🎧 For: Open-source music format
📍 Where: Podcasts, games
🛠️ Open with: VLC, Foobar2000
.pdf – Portable Document Format
📚 For: Fixed-layout docs
📍 Where: Everywhere—manuals, resumes, tax forms
🛠️ Open with: Adobe Reader, browser, PDF24
.php – PHP Script
💻 For: Dynamic websites
📍 Where: Web hosting
🛠️ Open with: Code editor
⚠️ Server-side script—don’t click it if you’re unsure.
.png – Image (with transparency)
🖼️ For: High-quality graphics
📍 Where: Web design, screenshots
🛠️ Open with: Image viewer, Photoshop
.ppt / .pptx – PowerPoint Presentation
📊 For: Slideshows
📍 Where: Business, school
🛠️ Open with: PowerPoint, Google Slides
.psd – Photoshop Document
🎨 For: Editable images
📍 Where: Graphic designers
🛠️ Open with: Photoshop
.rar – Compressed Archive
📦 For: Bundled files
📍 Where: Downloads
🛠️ Open with: WinRAR, 7-Zip
⚠️ Can hide viruses—scan before opening.
.rtf – Rich Text Format
📝 For: Styled text documents
📍 Where: WordPad, older documents
🛠️ Open with: Word, Notepad
.svg – Scalable Vector Graphic
📐 For: Web/vector images
📍 Where: Websites, graphic design
🛠️ Open with: Web browser, Inkscape
.sys – System File
⚙️ For: Windows operations
📍 Where: System folders
🛠️ Open with: You don’t!
⚠️ Deleting these = digital regret.
.tar – Unix Archive
📦 For: Grouped files (often Linux)
📍 Where: Linux systems
🛠️ Open with: 7-Zip, WinRAR
.tex – LaTeX Document
📚 For: Academic papers
📍 Where: Universities, research
🛠️ Open with: TeXworks, Overleaf
.tif / .tiff – High-Quality Image
📸 For: Printing, scanning
📍 Where: Design and photography
🛠️ Open with: Photoshop, image viewer
.tmp – Temporary File
🕑 For: Mid-process files
📍 Where: App folders
🛠️ Open with: Usually disposable
⚠️ Safe to delete after use (or system restart).
.ts – Transport Stream
📺 For: Broadcast video
📍 Where: Recorded TV shows
🛠️ Open with: VLC
.txt – Plain Text
📃 For: Notes, logs, anything
📍 Where: Everywhere
🛠️ Open with: Notepad, Word
.url – Internet Shortcut
🌐 For: Saved website links
📍 Where: Desktop or folders
🛠️ Open with: Any browser
.vbs – VBScript
🧨 For: Scripted commands
📍 Where: System automation
🛠️ Open with: Notepad
⚠️ Can run dangerous commands—don’t open random .vbs files!
.wav – Audio File
🔊 For: High-quality sound
📍 Where: Audio production
🛠️ Open with: VLC, Audacity
.webm – Web Video
📹 For: Streaming and websites
📍 Where: YouTube, web apps
🛠️ Open with: Browser, VLC
.wma – Windows Media Audio
🎼 For: Microsoft music format
📍 Where: Older music libraries
🛠️ Open with: Windows Media Player
.wmv – Windows Media Video
🎥 For: Video files
📍 Where: Windows apps
🛠️ Open with: Windows Media Player
.xls / .xlsx – Excel Spreadsheet
📈 For: Data, budgets, tables
📍 Where: Work, school
🛠️ Open with: Excel, Google Sheets
.xml – eXtensible Markup Language
📦 For: Data structure
📍 Where: Web & app config
🛠️ Open with: Notepad, code editor
.zip – Compressed Archive
📦 For: Bundled files
📍 Where: Downloads
🛠️ Open with: Windows built-in unzipper, 7-Zip
🚨 Honorable Mention: Extensions to Be Cautious About
| Extension | Why It’s Sketchy |
|---|---|
| .exe | Can install malware |
| .bat | Can run commands |
| .vbs | Can modify system behavior |
| .js | JavaScript can run scripts |
| .scr | Screensaver, but can be a virus |
| .cmd | Like .bat, can run commands |
| .jar | Java programs—can be dangerous |
| .lnk | Can disguise file paths |
Rule of Thumb: If someone emails you a file ending in any of the above and says “Open this, it’s hilarious,” just… don’t.