{
  "title": "MCP Discovery vs A2A Agent Cards",
  "schemaVersion": "1.0",
  "researchFreeze": "2026-08-26",
  "protocolRevision": "MCP 2026-07-28 / A2A 1.0",
  "mcpRevision": "2026-07-28",
  "a2aCompatibilityLine": "1.0",
  "a2aWebsiteSpecificationLabel": "1.0.0",
  "a2aRepositoryPatchTag": "v1.0.1",
  "a2aVersionSemantics": "A2A negotiates major.minor 1.0; patch tags identify specification releases and are not negotiated.",
  "count": 12,
  "records": [
    {
      "Dimension": "Primary object",
      "MCP": "DiscoverResult and primitive lists",
      "A2A": "AgentCard",
      "id": "R8-DISC01",
      "packageSourceIds": [
        "S003",
        "S006",
        "S044"
      ],
      "sourceIds": [
        "S339",
        "S342",
        "S127"
      ]
    },
    {
      "Dimension": "Primary method",
      "MCP": "server/discover (servers MUST implement it; the client preflight call is optional), then primitive list methods",
      "A2A": "GET well-known Agent Card, direct URL, registry or authenticated extended card",
      "id": "R8-DISC02",
      "packageSourceIds": [
        "S003",
        "S006",
        "S044"
      ],
      "sourceIds": [
        "S339",
        "S342",
        "S127"
      ],
      "packageSnapshot": "server/discover (optional), then tools/list/resources/list/prompts/list",
      "editorialCorrection": "Distinguished mandatory server support from an optional client preflight call."
    },
    {
      "Dimension": "Standard public location",
      "MCP": "No universal well-known server-card path in current core",
      "A2A": "/.well-known/agent-card.json",
      "id": "R8-DISC03",
      "packageSourceIds": [
        "S003",
        "S006",
        "S044"
      ],
      "sourceIds": [
        "S339",
        "S342",
        "S127"
      ]
    },
    {
      "Dimension": "Advertised identity",
      "MCP": "serverInfo implementation metadata",
      "A2A": "name, description, provider, documentation, icon",
      "id": "R8-DISC04",
      "packageSourceIds": [
        "S003",
        "S006",
        "S044"
      ],
      "sourceIds": [
        "S339",
        "S342",
        "S127"
      ]
    },
    {
      "Dimension": "Advertised protocol support",
      "MCP": "supportedVersions",
      "A2A": "supportedInterfaces with URL, protocolBinding and protocolVersion",
      "id": "R8-DISC05",
      "packageSourceIds": [
        "S003",
        "S006",
        "S044"
      ],
      "sourceIds": [
        "S339",
        "S342",
        "S127"
      ]
    },
    {
      "Dimension": "Advertised capabilities",
      "MCP": "tools/resources/prompts/extensions summary plus later lists",
      "A2A": "capabilities and skills",
      "id": "R8-DISC06",
      "packageSourceIds": [
        "S003",
        "S006",
        "S044"
      ],
      "sourceIds": [
        "S339",
        "S342",
        "S127"
      ]
    },
    {
      "Dimension": "Authorization metadata",
      "MCP": "OAuth protected-resource and authorization-server metadata at protocol-defined locations",
      "A2A": "securitySchemes and securityRequirements in Agent Card; credentials acquired out of band",
      "id": "R8-DISC07",
      "packageSourceIds": [
        "S003",
        "S006",
        "S044"
      ],
      "sourceIds": [
        "S339",
        "S342",
        "S127"
      ]
    },
    {
      "Dimension": "Signatures",
      "MCP": "No general core server-card signature object",
      "A2A": "Optional JWS Agent Card signatures with canonicalization",
      "id": "R8-DISC08",
      "packageSourceIds": [
        "S003",
        "S006",
        "S044"
      ],
      "sourceIds": [
        "S339",
        "S342",
        "S127"
      ]
    },
    {
      "Dimension": "Caching",
      "MCP": "Discover/list results carry cache hints in current MCP",
      "A2A": "HTTP caching guidance for Agent Cards",
      "id": "R8-DISC09",
      "packageSourceIds": [
        "S003",
        "S006",
        "S044"
      ],
      "sourceIds": [
        "S339",
        "S342",
        "S127"
      ]
    },
    {
      "Dimension": "Sensitive metadata",
      "MCP": "Server may reveal only capabilities after auth/policy",
      "A2A": "Authenticated extended Agent Cards and selective registry disclosure",
      "id": "R8-DISC10",
      "packageSourceIds": [
        "S003",
        "S006",
        "S044"
      ],
      "sourceIds": [
        "S339",
        "S342",
        "S127"
      ]
    },
    {
      "Dimension": "Dynamic catalogs",
      "MCP": "Primitive list methods and roadmap progressive discovery",
      "A2A": "Agent Card update, registry, or direct configuration",
      "id": "R8-DISC11",
      "packageSourceIds": [
        "S003",
        "S006",
        "S044"
      ],
      "sourceIds": [
        "S339",
        "S342",
        "S127"
      ]
    },
    {
      "Dimension": "Trust implication",
      "MCP": "Discovery says what the server claims to expose",
      "A2A": "Agent Card says what the agent claims to be able to do; both require independent trust and authorization controls",
      "id": "R8-DISC12",
      "packageSourceIds": [
        "S003",
        "S006",
        "S044"
      ],
      "sourceIds": [
        "S339",
        "S342",
        "S127"
      ]
    }
  ]
}