File formats
What the extension means, what opens it, and the thing about it that actually catches people out.
Image
| Extension | Format |
|---|---|
| .heic | High Efficiency Image Container |
| .webp | WebP Image |
| .avif | AV1 Image File Format |
| .svg | Scalable Vector Graphics |
| .psd | Photoshop Document |
| .ai | Adobe Illustrator Artwork |
| .raw | Camera Raw Image |
Document
| Extension | Format |
|---|---|
| Portable Document Format | |
| .docx | Word Document |
| .epub | Electronic Publication |
Data
| Extension | Format |
|---|---|
| .csv | Comma-Separated Values |
| .json | JavaScript Object Notation |
| .yaml | YAML Ain't Markup Language |
| .sql | SQL Script |
| .parquet | Apache Parquet |
Archive
| Extension | Format |
|---|---|
| .zip | ZIP Archive |
| .7z | 7-Zip Archive |
| .tar | Tape Archive |
| .iso | Disc Image |
Video
| Extension | Format |
|---|---|
| .mp4 | MPEG-4 Video |
| .mov | QuickTime Movie |
| .mkv | Matroska Video |
| .webm | WebM Video |
Audio
| Extension | Format |
|---|---|
| .mp3 | MPEG Audio Layer III |
| .flac | Free Lossless Audio Codec |
| .wav | Waveform Audio |
Font
| Extension | Format |
|---|---|
| .ttf | TrueType Font |
| .woff2 | Web Open Font Format 2 |
Executable
| Extension | Format |
|---|---|
| .exe | Windows Executable |
| .dmg | Apple Disk Image |
| .apk | Android Package |
Text
| Extension | Format |
|---|---|
| .log | Log File |
| .env | Environment File |
The extension is a hint, not a fact
A file's extension is just the end of its name — renaming photo.png to photo.jpg changes nothing about the bytes inside. What programs actually rely on is the magic number, the first few bytes of the file: %PDF for a PDF, PK for anything ZIP-based, \x89PNG for a PNG. On Unix, file somefile reports what a file really is regardless of its name.
Formats that are secretly ZIP files
DOCX, XLSX, PPTX, EPUB, JAR, APK and IPA are all ZIP archives with a mandated internal layout. Rename any of them to .zip, extract it, and you can read the XML or class files inside — genuinely useful when a document will not open and you need to recover the text.