SKILL.md
A markdown file at the root of a domain, with YAML frontmatter naming the skill, that tells an agent what the site can do for it. A 200 that carries HTML is a soft 404, not a file. Measured in agent surfaces without a score: adoption is early and absence says nothing about the site.
Terms this definition uses
Machine files
The files addressed to machines rather than readers, and what publishing one does and does not buy.
llms.txt · llms-full.txt · agents.md · entity map · entity map parity · machine layer · well-known URI · MCP · agent card · sitemap index · OpenAPI specification · ai.txt · Tool definition · sitemap origin error · soft 404 on a machine file · tdmrep.json · TDM exception · security.txt
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