{
  "schema": "a2atraffic-protocol-v1",
  "_comment": "Facts about the A2A protocol that this site is permitted to print. Every entry was re-derived from a primary source on the verified_at date; build-site.mjs emits nothing about the protocol that is not in this file, and launch-gate.mjs refuses to publish when the emitted page and this record disagree. If you cannot cite it here, the page may not say it.",

  "protocol": "A2A (Agent2Agent)",
  "latest_version": "1.0",
  "verified_at": "2026-08-17",
  "verified_against": "a2a-protocol.org/latest/specification/ and a2aproject/A2A@main/specification/a2a.proto",

  "governance": {
    "body": "Linux Foundation",
    "committee": "Technical Steering Committee",
    "tsc_members": ["AWS", "Cisco", "Google", "IBM Research", "Microsoft", "Salesforce", "SAP", "ServiceNow"],
    "origin": "Created by Google, announced April 2025, donated to the Linux Foundation June 2025.",
    "aaif_note": "Reported August 2026: Google is transferring A2A into the Agentic AI Foundation, the Linux Foundation entity formed 2025-12-09 that already holds MCP, goose and AGENTS.md. Stated here as reported, not as verified — the primary source cited for it returned HTTP 403 and could not be read.",
    "aaif_rung": "reported"
  },

  "adoption": {
    "organizations": "150+",
    "github_stars": "22,000+",
    "sdk_languages": ["Python", "JavaScript", "Java", "Go", ".NET"],
    "as_of": "2026-04-09",
    "_comment": "Linux Foundation press release, one-year mark. The number is theirs, not ours, and the date is April — do not re-date it to today."
  },

  "discovery": {
    "well_known_path": "/.well-known/agent-card.json",
    "rfc": "RFC 8615",
    "quote": "The standard path is https://{agent-server-domain}/.well-known/agent-card.json, following the principles of RFC 8615.",
    "superseded_path": "/.well-known/agent.json",
    "superseded_note": "An earlier-draft path. It is the one this site shipped until 2026-08-17.",
    "mechanisms": [
      { "name": "Well-Known URI", "detail": "The agent hosts its card at the standardised path. Public or domain-controlled discovery." },
      { "name": "Curated registries", "detail": "A catalog service holds cards and answers queries by skill or tag. The spec does not yet prescribe a registry API." },
      { "name": "Direct configuration", "detail": "Hardcoded details, config files, environment variables. For known, static relationships." }
    ]
  },

  "bindings": [
    { "id": "JSONRPC", "label": "JSON-RPC 2.0", "detail": "The original binding. Methods are called by name over a single endpoint." },
    { "id": "GRPC", "label": "gRPC", "detail": "Address form is hostname:port, e.g. grpc.example.com:443." },
    { "id": "HTTP+JSON", "label": "HTTP+JSON / REST", "detail": "Custom-verb paths, e.g. POST /message:send. The /v1 prefix was dropped in 1.0." }
  ],
  "_bindings_comment": "a2a.proto:341-344 — 'This is an open form string... The core ones officially supported are JSONRPC, GRPC and HTTP+JSON.' Three is the count of officially supported bindings, not a closed set.",

  "task_states": [
    { "id": "TASK_STATE_UNSPECIFIED", "short": "unspecified", "kind": "unknown", "detail": "The task is in an unknown or indeterminate state." },
    { "id": "TASK_STATE_SUBMITTED", "short": "submitted", "kind": "open", "detail": "Successfully submitted and acknowledged." },
    { "id": "TASK_STATE_WORKING", "short": "working", "kind": "open", "detail": "Actively being processed by the agent." },
    { "id": "TASK_STATE_INPUT_REQUIRED", "short": "input-required", "kind": "interrupted", "detail": "The agent requires additional user input to proceed." },
    { "id": "TASK_STATE_AUTH_REQUIRED", "short": "auth-required", "kind": "interrupted", "detail": "Authentication is required to proceed." },
    { "id": "TASK_STATE_COMPLETED", "short": "completed", "kind": "terminal", "detail": "Finished successfully. Terminal." },
    { "id": "TASK_STATE_FAILED", "short": "failed", "kind": "terminal", "detail": "Finished with an error. Terminal." },
    { "id": "TASK_STATE_CANCELED", "short": "canceled", "kind": "terminal", "detail": "Canceled before completion. Terminal." },
    { "id": "TASK_STATE_REJECTED", "short": "rejected", "kind": "terminal", "detail": "The agent decided not to perform the task. Terminal." }
  ],
  "_task_states_comment": "a2a.proto:187-208, in declaration order, re-ordered here open -> interrupted -> terminal for reading. Nine values including UNSPECIFIED.",

  "roles": [
    { "id": "ROLE_USER", "was": "user" },
    { "id": "ROLE_AGENT", "was": "agent" }
  ],

  "methods": [
    { "v1": "SendMessage", "v03": "message/send", "detail": "Send a message; may create a task." },
    { "v1": "SendStreamingMessage", "v03": "message/stream", "detail": "Same, with a stream of updates back." },
    { "v1": "GetTask", "v03": "tasks/get", "detail": "Read one task." },
    { "v1": "ListTasks", "v03": "— (new in 1.0)", "detail": "Enumerate tasks. Cursor-paginated." },
    { "v1": "CancelTask", "v03": "tasks/cancel", "detail": "Request cancellation." },
    { "v1": "SubscribeToTask", "v03": "tasks/resubscribe", "detail": "Re-attach to a task's event stream." },
    { "v1": "GetExtendedAgentCard", "v03": "agent/getAuthenticatedExtendedCard", "detail": "Fetch the authenticated extended card." },
    { "v1": "CreateTaskPushNotificationConfig", "v03": "tasks/pushNotificationConfig/set", "detail": "Register a push target for a task." }
  ],

  "changes_v03_to_v10": [
    { "area": "Agent Card", "from": "url, preferredTransport, additionalInterfaces, protocolVersion at top level", "to": "supportedInterfaces[] — each entry carries url, protocolBinding, protocolVersion, tenant", "why": "One ordered list, first entry preferred. Protocol version is now per-interface, so an agent can serve 0.3 and 1.0 side by side." },
    { "area": "Task state", "from": "\"working\"", "to": "\"TASK_STATE_WORKING\"", "why": "All states became SCREAMING_SNAKE_CASE with a TASK_STATE_ prefix. Nine values." },
    { "area": "Message role", "from": "\"user\" / \"agent\"", "to": "\"ROLE_USER\" / \"ROLE_AGENT\"", "why": "Same normalisation." },
    { "area": "Part", "from": "separate TextPart / FilePart / DataPart with a kind discriminator", "to": "one Part with oneof content: text, raw, url, data", "why": "Discriminate by member presence — 'text' in part — not by part.kind. mimeType became mediaType; filename applies to all kinds." },
    { "area": "Stream events", "from": "{ kind: \"status-update\", …, final: true }", "to": "{ statusUpdate: { … } } / { artifactUpdate: { … } }", "why": "Wrapper-based discrimination. The final boolean is gone; closing the stream signals completion." },
    { "area": "HTTP+JSON paths", "from": "POST /v1/message:send", "to": "POST /message:send", "why": "The /v1 prefix was dropped; version lives on the interface." },
    { "area": "Pagination", "from": "page / perPage", "to": "cursor / limit / nextCursor", "why": "Cursor-based." },
    { "area": "Errors", "from": "RFC 9457 application/problem+json", "to": "google.rpc.Status + ErrorInfo, application/json", "why": "Errors carry a details[] with reason in UPPER_SNAKE_CASE and domain a2a-protocol.org." },
    { "area": "OAuth", "from": "implicit and password flows", "to": "device code (RFC 8628); pkce_required on authorization code", "why": "The two deprecated flows were removed." },
    { "area": "Agent Card trust", "from": "unsigned", "to": "signatures[] — JWS (RFC 7515) over JCS-canonicalised JSON (RFC 8785)", "why": "A card can now be cryptographically bound to a domain." },
    { "area": "Multi-tenancy", "from": "—", "to": "tenant on every request and on AgentInterface", "why": "Route to one agent among many behind a shared endpoint." },
    { "area": "Capabilities", "from": "supportsAuthenticatedExtendedCard at top level", "to": "capabilities.extendedAgentCard", "why": "Moved inside the capability set." }
  ],

  "agent_card_required_fields": ["name", "description", "supportedInterfaces", "version", "capabilities", "defaultInputModes", "defaultOutputModes", "skills"],
  "agent_card_optional_fields": ["provider", "documentationUrl", "securitySchemes", "securityRequirements", "signatures", "iconUrl"],
  "_agent_card_fields_comment": "a2a.proto:362-399. REQUIRED is google.api.field_behavior on the proto field, read directly, not inferred from an example.",

  "vs_mcp": {
    "mcp": "Agent to tool. An agent reaches a server to call a tool or read a resource.",
    "a2a": "Agent to agent. Two independent agents discover each other, delegate a task, and exchange artifacts.",
    "quote": "The A2A documentation states the two are 'highly complementary' and 'designed to work together'.",
    "note": "They are not competitors and a system usually runs both: A2A across the agent graph, MCP down from each agent to its tools. Both are now Linux Foundation projects."
  },

  "mcp_current": {
    "_comment": "Tracked here because this site draws the A2A/MCP boundary and MCP moved. Read from the MCP blog on verified_at.",
    "version": "2026-07-28",
    "naming": "The spec identifies itself by date — the version string is \"2026-07-28\". The official C# SDK calls its implementation v2.0 and much of the coverage calls it MCP 2; the specification does not.",
    "billed_as": "the largest revision of the protocol since it launched",
    "changes": [
      "Stateless core — from a bidirectional stateful protocol to request/response. Requests are self-describing and can land on any instance behind a load balancer.",
      "An Extensions framework, with Tasks moved out of experimental core into the io.modelcontextprotocol/tasks extension (poll-based retrieval and update).",
      "MCP Apps and Enterprise Managed Authorization as extensions.",
      "Multi Round-Trip Requests, replacing server-initiated requests that needed a held-open stream — mid-call user interaction without statefulness.",
      "Authorization hardening: RFC 9207 issuer validation, Dynamic Client Registration replaced by Client ID Metadata Documents, credentials bound to the issuing authorization server.",
      "A formal deprecation policy. Roots, Sampling and Logging are deprecated, as is the legacy HTTP+SSE transport, on a twelve-month minimum window."
    ],
    "what_it_does_not_add": "Nothing for agent-to-agent communication, and nothing for governance — no membership, deliberation, voting, dissent preservation, human escalation or tamper-evident replay.",
    "why_that_matters_here": "It sharpens the boundary rather than blurring it. Both protocols now have a task concept, so 'A2A has tasks, MCP does not' is no longer the distinction — the distinction is the axis: MCP went further down toward tools and infrastructure, A2A stays across peers. And a stateless MCP makes the governance question louder, not quieter: a protocol that deliberately holds no session state is not the layer that will remember who was permitted to do what.",
    "source": "https://blog.modelcontextprotocol.io/posts/2026-07-28/"
  },

  "sources": {
    "spec": "https://a2a-protocol.org/latest/specification/",
    "whats_new": "https://a2a-protocol.org/latest/whats-new-v1/",
    "discovery": "https://a2a-protocol.org/latest/topics/agent-discovery/",
    "proto": "https://github.com/a2aproject/A2A/blob/main/specification/a2a.proto",
    "adoption": "https://www.linuxfoundation.org/press/a2a-protocol-surpasses-150-organizations-lands-in-major-cloud-platforms-and-sees-enterprise-production-use-in-first-year",
    "aaif": "https://www.linuxfoundation.org/press/linux-foundation-announces-the-formation-of-the-agentic-ai-foundation"
  }
}