mhtml

MHTML, short for MIME HTML, is a web archive format that bundles an HTML document and its embedded resources—such as images, stylesheets, and scripts—into a single file. It uses MIME encoding and is commonly saved with the .mht or .mhtml file extension. The format was standardized under RFC 2557, MIME Encapsulation of Aggregate HTML Documents, and relies on the multipart/related MIME type to combine the root document with its resources.

Inside an MHTML file, the content is organized as a multipart/related container. The root HTML is one part, while images, CSS, and other linked assets are additional parts each identified by a Content-Location header that preserves their original URLs. Resources may be base64-encoded or stored in binary form. Because everything is embedded, the file is self-contained and can be opened offline by compatible software.

Usage and compatibility: MHTML is used to preserve and share complete web pages in a single file. It was commonly supported by Microsoft Internet Explorer and some other browsers and tools. In modern web environments, support is inconsistent; several browsers either do not offer an MHTML save option or have removed it, and some users rely on third-party converters to generate or view MHTML archives.

Limitations: Dynamic content generated at runtime may not render correctly, and embedded resources can lead to larger file sizes. Security and privacy concerns have been noted, as embedded scripts or cross-origin resources might pose risks when viewing on untrusted hosts. Consequently, MHTML has largely declined in prominence in favor of lighter formats or separate resource packaging.