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MCP

Global Agent Bureau is an agent bureau and a technology company. The license is PolyForm Noncommercial 1.0.0.

POST /mcp is a remote MCP server on the streamable HTTP transport. It exposes the bureau tools on top of the existing API. It does not keep a second copy of scores. A key that starts with gab_test_ uses the sandbox partition on this branch: test rows do not change a production score.

Protocol version

Verified on 16 October 2026 against protocol revision 2026-07-28. Pages opened:

  • https://modelcontextprotocol.io/specification/2026-07-28
  • https://modelcontextprotocol.io/specification/2026-07-28/basic/transports
  • https://modelcontextprotocol.io/specification/2026-07-28/basic/transports/streamable-http
  • https://modelcontextprotocol.io/specification/2026-07-28/basic/versioning
  • https://modelcontextprotocol.io/specification/2026-07-28/basic/authorization
  • https://modelcontextprotocol.io/specification/2026-07-28/server/discover
  • https://modelcontextprotocol.io/specification/2026-07-28/server/tools
  • https://modelcontextprotocol.io/specification/2026-07-28/changelog

server/discover returns supportedVersions: ["2026-07-28"]. A different MCP-Protocol-Version receives HTTP 400 and JSON-RPC code -32022 (UnsupportedProtocolVersionError) with that list. This revision has no initialize handshake and no protocol session. GET and DELETE on /mcp receive HTTP 405. Mcp-Session-Id and Last-Event-ID are ignored.

Request shape

Each JSON-RPC message is its own POST with Content-Type: application/json. The response is one JSON object (application/json), not a long-lived event stream. These tools finish in that one object.

Required headers:

  • MCP-Protocol-Version: 2026-07-28
  • Mcp-Method, equal to the JSON-RPC method
  • Mcp-Name on tools/call, equal to params.name

params._meta must include io.modelcontextprotocol/protocolVersion with the same value as the header. A mismatch is HTTP 400 and code -32020 (HeaderMismatch).

Accept may list application/json and text/event-stream. A present Accept that allows neither application/json nor */* is refused.

An Origin header must match the request host. A browser origin that does not match receives HTTP 403. Clients that omit Origin are accepted.

Authentication

Send Authorization: Bearer and a bureau API key. tools/list and tools/call require that key. server/discover does not.

The MCP authorization section (OAuth 2.1, protected-resource metadata, RFC 9728) is optional in the spec. This server does not implement that OAuth flow. It accepts the bureau API keys that already exist. A missing or unknown key receives HTTP 401 and WWW-Authenticate: Bearer. A portal session is not an API key and is refused. The raw key is not written into the response, the audit row, or the log line.

A gab_test_ key sets the sandbox test partition for that request. On a deployment with GAB_ENV=sandbox, a live key is refused with the same rule as the HTTP API.

tools/list returns only the tools the key's scopes allow. verify_agent needs verify, inquire needs inquire, and report needs report. check_revocation and fetch_signed_receipt are available to any API key.

Tools

Tool What it does
verify_agent Checks action against the stored intent agreement. Result is ALLOW, DENY, or STEP_UP.
verify_checkout Checks a v2026-08-25 checkout as an action. Registered only when GAB_ENV is sandbox, and only for a gab_test_ key. The bureau does not host checkout.
inquire Reads status, authorizations, revocation notes, incident counts, and the trust score for a purpose code. The read does not change the score.
report Files transaction_outcome, fraud_incident, chargeback, or policy_violation. evidence_hash is sha256: and 64 hex characters.
check_revocation Reads the public revocation list. Optional agent_id also returns that agent's status in this key's partition.
fetch_signed_receipt Reads one signed transparency-log entry by sequence. A missing sequence returns a tool error: a signed log entry is not available.

A business-rule failure (unknown agent, bad purpose code, missing evidence) is HTTP 200 with result.isError: true. An unknown tool name is HTTP 400 and code -32602.

Limits

Tool requests share the HTTP rate limits. verify_agent and verify_checkout count toward GAB_VERIFY_RATE_LIMIT_PER_MINUTE (default 60). inquire counts toward GAB_INQUIRY_RATE_LIMIT_PER_MINUTE (default 30). report counts toward GAB_REPORT_RATE_LIMIT_PER_MINUTE (default 10). Every POST /mcp also counts toward GAB_RATE_LIMIT_PER_MINUTE (default 120). Over the limit the response is HTTP 429 and rate limit exceeded.

Example

POST /mcp HTTP/1.1
Authorization: Bearer YOUR_KEY
Accept: application/json, text/event-stream
Content-Type: application/json
MCP-Protocol-Version: 2026-07-28
Mcp-Method: tools/call
Mcp-Name: inquire

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "tools/call",
  "params": {
    "name": "inquire",
    "arguments": {
      "agent_id": "shopper-01",
      "purpose_code": "payment_authorization"
    },
    "_meta": {
      "io.modelcontextprotocol/protocolVersion": "2026-07-28",
      "io.modelcontextprotocol/clientInfo": {"name": "example", "version": "1"},
      "io.modelcontextprotocol/clientCapabilities": {}
    }
  }
}

Replace YOUR_KEY with a key issued to your organization. Do not commit a real key.