Extension
A human-facing convention. Easy to change and not guaranteed to match the bytes.
A compact reference for everyday files
Know what is inside the extension.
Compare common formats by structure, media type, capabilities, and identifying bytes — without treating a filename as proof.
image/pngPNG
89 50 4E 47application/jsonJSON
UTF-8 · structured textapplication/zipZIP
50 4B 03 04Browse by family
Each section focuses on the decisions a format makes: text or binary, lossy or lossless, one stream or many entries, passive data or potentially active content.
.txt · .json · .csv
Text & data
Encoding, structure, delimiters, and the limits of “plain text.”
.png · .jpg · .webp · .svgImages
Pixels or vectors, lossy or lossless, still frames or animation.
.zip · .gz · .tarArchives
Bundling, compression, metadata, and why tar.gz has two suffixes.
offset · hex · ASCIIFile signatures
Recognizable headers, offsets, and the checks they cannot replace.
Three layers of identity
A useful identification combines several independent clues. Any one of them can be absent, ambiguous, or deliberately misleading.
Media type
Metadata such as an HTTP Content-Type. Useful when the sender labels the content correctly.
Structure
Headers, signatures, and parseable records. Stronger evidence, but still not a security verdict.
Reference scope
This guide covers common interchange formats rather than every variant. Exact conformance belongs to the linked standards and format specifications.
Official names
Media types are checked against the IANA registry where a registration exists.
Byte-aware
Signatures are shown with offsets and caveats instead of presented as universal magic.
No uploads
No file leaves your device because the site does not accept or inspect files.