Gwtar

File Format
Name	Gwtar
Ontology	Electronic File Formats Archiving Hypermedia Gwtar
Extension(s)	.gwtar.html
MIME Type(s)	text/html, x-gwtar
Released	2026

Gwtar (pronounced like "guitar") is a format for storing a full webpage in a single HTML file, developed in 2026 by Gwern Branwen and Said Achmiz.

The format was developed as a convenient solution for archiving webpages, which would satisfy three criteria:

• the full contents of the webpage, including images, scripts, etc. must be stored locally;
• the webpage and all its assets must be stored as a single file;
• users can browse the archived webpage without having to first download the entire file (parts of the file with webpage assets are downloaded as needed).

A Gwtar file consists of three parts:

• the header - a combination of HTML, JavaScript, and JSON, which contains the actual HTML markup, as well as scripts which handle piece-by-piece download of the rest of the file;
• all of the webpage resources, stored in tarball format;
• any other arbitary data (e.g. metadata, electronic signatures, error correction codes).

Specifications

• Gwtar: a static efficient single-file HTML format, from gwern.net