The machine-readable surface AI agents talk to — llms.txt, sitemaps, feeds, public endpoints, and the 2026 cross-platform standards (A2A, UCP, WebMCP).
API Compatibility is the set of machine-readable surfaces that let agents index, talk to, and transact with your site without scraping it. A well-formed llms.txt, a fresh sitemap.xml, RSS feeds, and clean public endpoints are the foundation. On top of that, three 2026 cross-platform standards have emerged that AI agents from OpenAI, Google, Microsoft, and Anthropic are aligning around: A2A AgentCard for agent-to-agent discovery, Universal Commerce Protocol (UCP) for AI-driven checkout, and WebMCP for runtime tool registration in Chrome. Sites that implement these are visible to the agentic web; sites that don't are invisible to it.
Modern agents prefer llms.txt and sitemap.xml when available, then fall back to scraping. Cross-vendor agents discover peer services via A2A AgentCard at /.well-known/agent-card.json. Gemini and Google AI Mode in Search negotiate transactions via UCP profiles at /.well-known/ucp. Gemini in Chrome actuates page-level tools via the WebMCP runtime API. A site with a clean machine-readable surface gets indexed faster, transacts with agents directly, and doesn't lose to competitors that did the work to publish these standards.
A valid llms.txt at the site root listing primary pages and intent
A sitemap.xml with real, varied lastmod dates per URL
/.well-known/agent-card.json declaring the site's agent identity and skills (A2A protocol)
/.well-known/ucp declaring checkout services and capabilities (Google UCP — for commerce sites)
navigator.modelContext exposing page tools at runtime (WebMCP — Chrome 149 origin trial)
The free audit returns your score on this pillar plus the other 4 — and tells you which specific findings are dragging it down.
Free AAO Audit01
The Schema.org markup that lets agents extract facts before they read prose.
02
Readable, extractable answers — the substrate AI agents quote.
04
How clearly your reputation is declared in your site's schema and content — what agents can parse without leaving your domain.
05
How recently you've shown agents you're still here — and still right.