WellKnownMCP — Specification for .llmfeed.json feeds

WellKnownMCP defines an open convention for publishing structured, signed .llmfeed.json feeds to enable safe and trustworthy interactions between LLMs, agents, and the Web.

It is the reference spec for feeds used in the emerging Agentic Web.

What is a LLMFeed?

A .llmfeed.json file lets an agent understand:

  • The intent of a page or service
  • The capabilities it exposes (with optional OpenAPI)
  • The prompts it should react to
  • The cost or trust associated with an action
  • The guidance or behaviour expectations intended by the publisher

It also allows verification of:

  • Origin (origin field in metadata)
  • Signed blocks (trust.signed_blocks)
  • Certification (certification block, optional)

Core Feed Types

Feed Type Purpose
mcp Describe a service or API
export Export page content for agents
prompt Define reusable prompts
session Carry agent session context
credential Pass API credentials (with trust)
pricing Define pricing models

Trust and Signatures

Feeds may be:

✅ Signed (trust + signature)
✅ Certified (by an external CA such as llmca.org)

Agents SHOULD respect:

  • trust.signed_blocks to check which blocks are verifiably trusted
  • Certification level when applying agent behaviours

Feed Placement

Feeds may be:

  • Published in .well-known/llmfeed.json or .well-known/mcp.llmfeed.json
  • Served dynamically (for active MCP feeds)
  • Attached to APIs (OpenAPI extension)
  • Embedded in page metadata

Spec Structure

spec/
├── llmfeed.md                  # Core format
├── llmfeed_block-reference.md  # Canonical block reference
├── 02_feedtypes/               # Definitions of core feed types
├── 03_extensions/              # Extensions (signatures, API linkage...)
├── 04_agent-behavior/          # Optional expectations for agents consuming feeds
├── wellknown.md                # How to serve feeds via .well-known/

See also `agent-guidance.md` — for optional soft hints.

Agents and OpenAPI

Agents processing .llmfeed.json feeds may use:

  • capabilities[] for lightweight function definitions
  • OpenAPI for full API specs (referenced from capabilities block)

This allows hybrid approaches:

  • Lightweight LLM-first discovery
  • Full API fallback

Contributing

Contributions welcome!

  • Open issues or PRs to propose improvements.
  • Discuss extensions and future feed types.

🚀 Evolving Spec

The specification is living — new feed types and behaviours are proposed and reviewed openly.

Join us to help shape the future of the Agentic Web!