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ACT

Why ACT

The full canonical comparison lives in the v0.2 spec. This page is the marketing-front summary with the same conclusions.

TL;DR

  • vs /llms.txt and /llms-full.txt — ACT plugins auto-emit both files for back-compat. ACT adds typed nodes, hierarchy, i18n, schema validation, runtime delivery. Migration from llms.txt is zero-effort.
  • vs schema.org — different layer. schema.org is in-page semantics for individual elements; ACT is an out-of-band content tree. They compose.
  • vs sitemap.xml — sitemap is a URL list; ACT carries the actual content.
  • vs MCP alone — ACT defines the data shape; MCP is one transport. We ship a hosted MCP server (mcp.act-spec.org) so any MCP-capable agent can read any ACT-emitting site immediately.
  • vs custom REST endpoints — ACT is the shared schema everyone agrees on.

When to choose ACT

Choose ACT when:

  • Your site is large enough that llms.txt loses fidelity (more than ~50 pages or any non-trivial hierarchy).
  • You serve content in more than one locale and need first-class i18n.
  • You want schema-validated, conformance-testable content that consumers can rely on without bespoke onboarding.
  • You publish to AI agents and want it to work today via MCP, not “when vendors ship native support.”
  • You have runtime-rendered or per-tenant content the static formats cannot carry.

Stick with the simpler tools when:

  • A single static llms.txt is sufficient (small, single-locale, no hierarchy).
  • You only need search-engine SEO snippets — schema.org is the right layer.
  • You only need to advertise URLs — sitemap.xml is enough.

Migration paths

If you ship /llms.txt today, dropping in any ACT plugin keeps the file emitting (default-on) while adding the structured tree. Existing llms.txt consumers see no change.

If you ship a hand-written MCP server, ACT lets you delete most of the custom data-shape code and reuse the standard. See hybrid-static-runtime-mcp.

The hosted MCP

The single biggest reason to adopt ACT in v0.2 is the hosted MCP server. Every ACT-emitting site is immediately usable by any MCP-capable agent — Claude Desktop, Cursor, Continue, anything that speaks MCP.

See the homepage for the copy-paste client config and the tooling spec for transport details.

Read the full comparison

The detailed comparison table, prose, and conformance-band trade-offs live in the v0.2 spec — Why ACT.