agents.txt
An open specification for a machine-readable file, agents.txt, that lets a website declare which agent-interaction protocols it supports -- authorization, payments, MCP servers, skill packages, and A2A -- without embedding protocol implementation details.
agents.txt defines two files at a site's root: /agents.txt, which states which protocols the site supports, and /agents.json, which carries the structured detail an agent needs to use each one in a single request instead of crawling pages or probing endpoints. It positions itself as the fourth layer of an agent-readiness stack, after robots.txt for access, sitemap.xml for inventory, and llms.txt for content, announcing what an agent can actually do on the site.
The repository contains the specification text, a reference Astro site with demos deployed on Cloudflare Workers, an MCP server that exposes the spec to agents and can audit any URL for compliance, a Cloudflare Worker handling Ed25519 JWT-based agent authorization, a public audit page returning HTML, JSON, or Markdown, and a hosted JSON Schema for the agents.json format.
The format is protocol-agnostic and open to new blocks as further agent protocols emerge.