microformat

Microformats are a set of simple, open data formats designed to embed structured information in HTML webpages. Developed in the early 2000s, they aim to make certain kinds of information—such as people, events, and reviews—readable by both humans and software that can extract structured data from web pages. By using existing HTML, microformats provide a lightweight way to annotate content without creating separate data feeds or complex schemas.

Microformats rely on HTML class attributes to annotate content. A container with class "h-card" denotes a person or organization, and its properties use class names such as "p-name" for a name, "u-url" for a URL, and "dt-bday" for a birthday. This approach preserves human readability while enabling parsers to identify and extract the embedded data without requiring custom vocabularies.

Common microformats include h-card for contact information, h-calendar for events, h-review for user reviews, and h-resume for resumes. They are typically embedded in existing pages, allowing data to be harvested by aggregators, search engines, or personal data tools.

Microformats2 is a later revision that introduces a more uniform naming scheme and HTML5-friendly conventions. It uses prefixes like p-, u-, dt-, and e- for properties within h-* types such as h-card, h-event, and h-entry, emphasizing easier parsing and better compatibility with modern web authoring.

Adoption has varied. Some search engines and platforms have exploited microformats for data extraction and rich results, though many have shifted toward schema.org and other vocabularies. Limitations include limited expressiveness compared to formal ontologies, potential inconsistencies in markup, and reliance on visible HTML structure. Nonetheless, microformats remain a lightweight option for embedding portable, human- and machine-readable metadata in web pages.