File Formats You Actually Need to Know

“What file formats do I actually need to know about?” gets asked weekly on r/learnprogramming and r/computerscience. The honest answer: maybe 20 formats cover 95% of everyday usage. The rest are historical curiosities or domain-specific.

This guide is the practical taxonomy: the formats you’ll actually encounter, what they’re for, and the real differences between similar-looking ones (PNG vs JPG vs SVG, for example).

Document formats

• PDF (Portable Document Format): visual-fidelity-first. Looks the same on every device. Hard to edit. Default for sharing finished documents.
• DOCX (Microsoft Word): editable rich text + layout. Works in Word, Google Docs, LibreOffice, Pages. The default for collaborative drafting.
• ODT (OpenDocument Text): open-source DOCX equivalent. Used by LibreOffice. Round-trips with DOCX with minor formatting drift.
• RTF (Rich Text Format): simpler than DOCX, plain-ish text with basic formatting. Mostly historical; useful for compatibility with old or specialized software.
• TXT (plain text): just characters, no formatting. The universal lowest-common-denominator format.
• MD (Markdown): plain text with structural conventions (# for headings, * for bold, etc.). The format engineers and technical writers prefer.
• EPUB: reflowable ebook format. Used by Kindle (via conversion to AZW3), iBooks, Adobe Digital Editions. Better than PDF for reading on small screens.

Image formats: PNG, JPG, SVG, WebP, AVIF (the differences explained)

Each image format optimizes for something different:

• JPG / JPEG: lossy compression for photos. 30+ years old; universal compatibility. Use for: photos, photo-realistic images, anywhere you need maximum compatibility.
• PNG: lossless. Supports transparency. Use for: screenshots, line art, logos with transparency, anything with sharp edges.
• GIF: animated images, lossless palette compression (256 colors max). Mostly replaced by video formats and WebP/AVIF for animation. Still ubiquitous because of compatibility.
• SVG (Scalable Vector Graphics): vector format. Defined by math, not pixels — infinite resolution. Use for logos, icons, anything that needs to scale.
• WebP: Google’s modern format. Both lossy + lossless modes. 25–35% smaller than JPG/PNG at similar quality. Wide browser support. Use for web images.
• AVIF: newer than WebP, even better compression. Browser support reaching parity. Use for cutting-edge web; fallback to WebP for older browsers.
• HEIC / HEIF: Apple’s default for iPhone photos. Better compression than JPG. Compatibility outside Apple ecosystem is spotty — convert to JPG before sharing widely. Use our HEIC to JPG tool.
• BMP: uncompressed bitmap. Huge files. Mostly historical / Windows-specific.
• TIFF: high-quality lossless image. Used in publishing, scanning, professional photography. Big files.

Quick conversions on this site: PNG/JPG/WebP converter, SVG to PNG, HEIC to JPG, WebP to JPG.

Data formats: CSV, JSON, XML, YAML

• CSV (comma-separated values): oldest, simplest, spreadsheet-native. Each row is a line; columns separated by commas. Works with Excel, R, Python pandas, anything. Limitation: no nested data.
• JSON (JavaScript Object Notation): nested data structure. Web API default. Hierarchical objects + arrays. Most modern data exchange.
• XML (eXtensible Markup Language): hierarchical with attributes. Older than JSON; common in enterprise systems, SOAP APIs, document formats (DOCX, ODT internally are zipped XML). More verbose than JSON but more expressive (attributes, namespaces).
• YAML (YAML Ain’t Markup Language): human-friendly nested data. Used for configs (Kubernetes, Ansible, GitHub Actions). Indentation-sensitive — easy to break with whitespace.
• TOML: simpler than YAML for configs. Used by Cargo (Rust), Poetry (Python).
• Parquet, Avro, ORC: columnar binary formats for big data. Smaller and faster than CSV/JSON for analytics workloads. Used with Spark, BigQuery, Snowflake. Not human-readable.

Conversions on this site: JSON to CSV, CSV to JSON, XML to CSV, YAML ↔ JSON, CSV to Excel.

Audio + video formats

Quick reference:

• Audio lossless: WAV (uncompressed), FLAC (compressed lossless), ALAC (Apple lossless).
• Audio lossy: MP3 (universal), AAC (newer, better compression), OGG (open-source), Opus (best compression).
• Video lossy: H.264/MP4 (universal default), H.265/HEVC (better compression but patent-encumbered), VP9 (Google’s royalty-free), AV1 (newest royalty-free, best compression).
• Video containers: MP4, MOV, MKV, WebM, AVI. The container holds the codec — same H.264 video can be in MP4, MOV, or MKV.

Audio/video conversion on this site is intentionally limited — proper transcoding needs FFmpeg, which is too heavy for browser-only.

Archive + compression formats

• ZIP: universal, every OS supports. Combines lossless compression + multiple files in one archive.
• 7z: better compression than ZIP. Requires 7-Zip or compatible.
• RAR: proprietary. Was popular for piracy; declining.
• TAR: Unix archive (just bundles, no compression). Combined with gzip → .tar.gz, with bzip2 → .tar.bz2, with xz → .tar.xz.
• Single-file compression: gz, bz2, xz — compress one file at a time. Combined with TAR for archives of multiple files.

Converting between rare file formats

For unusual or domain-specific formats:

• 3D printing (STL, OBJ, 3MF, STEP): see our ebook + 3D conversion guide.
• CAD (DWG, DXF): AutoCAD’s DWG is proprietary; DXF is more open. Free tools: LibreCAD, FreeCAD, ODA File Converter.
• GIS (Shapefile, GeoJSON, KML): QGIS handles them all, free + open-source.
• DAW project files (.als, .flp, .logicx): proprietary, no clean cross-DAW conversion. Export stems as WAV/AIFF.
• E-reader formats (AZW3, MOBI, KFX): Calibre is the universal converter. KFX (Kindle’s newest) is partially supported.
• Genealogy (GEDCOM): universal genealogy format. Most genealogy software imports / exports it.

For truly rare formats, the workflow is: search GitHub for an open-source converter (often exists), or extract the underlying data via a library (most rare formats are zipped XML or binary with a published spec).