HTML (.html)
The markup language of the web. For agent output it gives people a designed, interactive page, at a token cost that depends on whether the agent re-invents the design each run.
- Specification
- WHATWG HTML Living Standard
- Media type
- text/html
- Works with
- CSS, SVG, JSON-LD / schema.org
Freeform HTML task boards cost 10.8k to 17.5k output tokens across runs in one benchmark; the same boards from a shared template kit cost 573 to 625.
Connected
- CSS (.css)Style sheets for HTML. In agent-generated pages it is most of the token bill, which is why template kits move it into one shared file.
- SVG (.svg)XML-based vector graphics. Hand-drawing diagrams in SVG forces a model to reason about coordinates, which can cost thousands of thinking tokens per diagram.
- Schema.orgA shared vocabulary for structured data, founded in 2011 by Google, Microsoft, Yahoo and Yandex, that search engines and AI systems use to understand pages.
- Markdown (.md)A plain-text formatting syntax that renders to HTML; the default format for agent instructions, plans and READMEs because it is cheap to generate, easy to diff and readable unrendered.
- agent-html-kitAn open-source template kit and Claude Code skill (kit.js) that lets agents emit content-only HTML components while design lives in one shared file, published with a 72-run HTML vs Markdown benchmark.
Linked from
- WCAG (Web Content Accessibility Guidelines)The W3C's testable accessibility standard for web content, organised around perceivable, operable, understandable and robust; version 2.2 is the current recommendation.
- ARIA live regionsPage areas marked with aria-live so screen readers announce their changes; the standard way to announce chat replies and status messages without moving focus.
- Global Privacy Control (GPC)A browser signal (the Sec-GPC: 1 header and navigator.globalPrivacyControl) telling sites not to sell or share the visitor's data; a legally valid opt-out in about a dozen US states.