Docs · Anchor Manifest v0.1 · draft

Anchor Manifest specification

There are good formats for describing a server, an API and an agent already. What's missing is one place per publisher that says which of those exist, how to reach each one, what it costs, which variant is safe to hand an agent, and whether anyone still maintains it. The manifest is that place. It's small on purpose and it links out instead of duplicating.

Design goals

Use existing protocols first. The manifest points at an MCP registry server.json, an OpenAPI document, an A2A agent card, an llms.txt and x402 discovery data. It doesn't restate any of them.
Add only what agents keep needing and nobody publishes. Read-only variants, per-call payment terms, status and changelog links, and a way to verify who published the file.
Be readable by a model with no prior knowledge, and small enough to fetch on every crawl.
Be optional. Tools without a manifest are still listed and scored. A manifest makes their facts more accurate and refreshes them faster.

Location and discovery

Serve the document at https://<publisher-domain>/.well-known/anchor.json with Content-Type: application/json and CORS enabled. Optionally advertise it with Link: </.well-known/anchor.json>; rel="anchor-manifest" on responses from the tool's own endpoints, and list it in llms.txt.

Document

{
  "anchor": "0.1",
  "publisher": {
    "name": "Example Search",
    "url": "https://example.com",
    "contact": "agents@example.com",
    "docs": "https://example.com/docs",
    "llmsTxt": "https://example.com/llms.txt"
  },
  "tools": [
    {
      "id": "com.example/search",
      "kind": "mcp",
      "name": "Example Search MCP",
      "description": "Web search and page fetch for agents.",
      "endpoint": "https://mcp.example.com/mcp",
      "transport": "streamable-http",
      "auth": ["none", "oauth2", "api-key"],
      "readOnlyVariant": "https://mcp.example.com/mcp/readonly",
      "scopedVariants": { "search-only": "https://mcp.example.com/mcp/search" },
      "payments": [
        { "protocol": "x402", "version": 2, "networks": ["eip155:8453", "solana:5eykt4UsFv8P8NJdTREpY1vzqKqZKvdp"], "asset": "USDC", "priceUsd": 0.005, "unit": "call", "discovery": "https://api.cdp.coinbase.com/platform/v2/x402/discovery/search?payTo=0x..." }
      ],
      "pricing": "https://example.com/pricing",
      "freeTier": { "cardRequired": false, "limit": "1000 calls/month" },
      "schemas": {
        "mcpServerJson": "https://registry.modelcontextprotocol.io/v0.1/servers/com.example%2Fsearch",
        "openapi": "https://api.example.com/openapi.json",
        "a2aAgentCard": null
      },
      "status": "https://status.example.com",
      "changelog": "https://example.com/changelog",
      "deprecations": [
        { "what": "/sse endpoint", "sunset": "2026-12-31", "replacement": "https://mcp.example.com/mcp" }
      ],
      "telemetry": { "collected": true, "optOut": "EXAMPLE_TELEMETRY=0", "policy": "https://example.com/privacy" },
      "security": "https://example.com/.well-known/security.txt",
      "source": "https://github.com/example/search-mcp",
      "license": "MIT"
    }
  ],
  "verify": {
    "dnsTxt": "_anchor.example.com",
    "http": "https://example.com/.well-known/anchor.json"
  },
  "updated": "2026-09-25"
}

Fields

Top level

Field	Required	Type	Notes
`anchor`	yes	string	Specification version, `"0.1"`
`publisher`	yes	object	`name`, `url` required. `contact`, `docs`, `llmsTxt` recommended
`tools`	yes	array	One entry per tool. May be empty for a publisher that only wants to be verified
`verify`	no	object	How the claim is verified, see below
`updated`	yes	date	ISO date the document last changed

Tool entry

Field	Required	Type	Notes
`id`	yes	string	Reverse-DNS identifier, the same form the MCP registry uses (`com.example/search`). Use the registry name if the tool is registered.
`kind`	yes	`mcp` · `http` · `openapi` · `a2a` · `sdk`	What kind of thing the endpoint is
`name`, `description`	yes	string	Short. A model reads them
`endpoint`	yes for hosted	URL	The primary hosted endpoint. Local-only tools use `packages` instead
`packages`	no	array of `{registry, name}`	npm, pypi, oci, nuget
`transport`	yes for `mcp`	`streamable-http` · `stdio` · `sse`	Declare `sse` only while it still works. List it under `deprecations` when retiring
`auth`	yes	array	Any of `none`, `oauth2`, `api-key`, `pat`, `httpsig`, `x402`. Order by preference.
`readOnlyVariant`	no	URL	An endpoint or mode that exposes no write tools. Strongly recommended, and scored.
`scopedVariants`	no	map	Named narrower endpoints
`payments[]`	no	array	`protocol` (`x402`, `mpp`, `l402`, `card`), `version`, `networks` (CAIP-2), `asset`, `priceUsd`, `unit` (`call`, `token`, `page`, `minute`), optional `discovery` URL
`pricing`	no	URL	Human pricing page readable without a login
`freeTier`	no	object	`cardRequired` boolean and a `limit` string
`schemas`	no	object	`mcpServerJson`, `openapi`, `a2aAgentCard`, `jsonSchema` URLs
`status`, `changelog`	recommended	URL	Scored under transparency
`deprecations[]`	no	array	`what`, `sunset` (date), `replacement`
`telemetry`	recommended	object	`collected` boolean, `optOut` instruction, `policy` URL
`security`	no	URL	Usually the publisher's `security.txt`
`source`, `license`	no	URL, SPDX id

Verification

A manifest is trusted for a listing when one of these holds.

DNS. A TXT record at _anchor.<publisher-domain> contains anchor-verify=<token>, where the token is issued when claiming the listing.
HTTP. The manifest is served from /.well-known/anchor.json on the same registrable domain as the tool's endpoint, and the endpoint responds. Same origin is the proof.
Registry. The id is a verified namespace in the official MCP registry and the registry's server.json lists the same endpoint.

A manifest that fails verification is ignored, not penalised. The crawler falls back to what it can observe.

How Anchor Terminal uses it

On every crawl the manifest is fetched, verified and diffed. Changed endpoints, prices, deprecations and variants update the listing's facts the same day. Declared deprecations with sunset dates count as graceful, never as negative events. A declared readOnlyVariant gets probed. If it exposes write tools, the declaration is marked false on the tool's page. Declared payments get probed with the same unpaid-request and canary-settlement method as any other x402 endpoint.

Relationship to other formats

Format	What it describes	How the manifest relates
MCP registry `server.json`	Packages and remotes of one server, with a verified namespace	Linked via `schemas.mcpServerJson`. The manifest reuses its `id`
OpenAPI	Operations of an HTTP API	Linked via `schemas.openapi`. RFC 9727 `/.well-known/api-catalog` stays the standard way to list OpenAPI documents
A2A agent card	Skills and interfaces of an agent	Linked via `schemas.a2aAgentCard`. The card stays at `/.well-known/agent-card.json`
llms.txt	Site index for LLMs	Linked from `publisher.llmsTxt`. The manifest should be listed in it
x402 Bazaar / `/.well-known/x402`	Payable resources and prices	Linked via `payments[].discovery`. Prices in the live `402` win
MCP server cards (`/.well-known/mcp/server-cards.json`, proposed)	Capabilities of MCP servers on a host	If adopted, the manifest will link to it. Until then the manifest carries the minimum needed

Status

Draft v0.1. Fields get added, not removed, before v1. Anchor Terminal publishes its own manifest at /.well-known/anchor.json.

Nobody outside this site publishes one yet, so the field list is our guess at what agents need rather than something worn in by use. The payments shape is the part I'd expect to change first, because MPP and L402 don't map cleanly onto priceUsd per unit. Feedback to agents@anchorterminal.com.