A2A Protocol
The Agent-to-Agent (A2A) protocol is a JSON-RPC 2.0 interface for inter-agent
communication. NANDA nodes expose a single POST /a2a endpoint that routes messages based
on action types.
Endpoint
POST /a2a
Content-Type: application/jsonRequest Format
All A2A messages follow the JSON-RPC 2.0 envelope with a nested message structure:
{
"jsonrpc": "2.0",
"method": "message/send",
"params": {
"message": {
"role": "user",
"parts": [{ "text": "{\"action\": \"certificate.check\", \"cert_id\": \"cert-abc-123\"}" }]
}
},
"id": "req-001"
}The text field inside parts[0] must be a JSON string containing an action field that determines the routing.
Supported Actions
certificate.revoke
Certifier · Implemented
Revoke a W3C Verifiable Credential by cert ID. Requires cert_id (string) and
optional reason (string). Updates the Bitstring Status List revocation bitmap.
certificate.check
Certifier · Implemented
Check whether a certificate has been revoked. Requires cert_id (string). Returns
revocation status and Bitstring Status List index.
start · status · certificate
Certifier · Implemented
Certification lifecycle — start a capability evaluation, check progress, and retrieve the issued credential.
policy.*
Compliance · Implemented
Compliance policy management — create, evaluate, and enforce governance rules for registered agents.
observer.* · telemetry.* · reputation
Observer · Implemented
Liveness probes, latency telemetry, and reputation scoring for registered agents.
audit.*
Auditor · Implemented
Payment intent reconciliation, settlement verification, and wallet management for x402-NP agent transactions.
Response Format
Successful responses return a JSON-RPC 2.0 result with the same A2A message envelope:
{
"jsonrpc": "2.0",
"result": {
"role": "agent",
"parts": [{ "text": "{\"status\": \"revoked\", \"cert_id\": \"cert-abc-123\"}" }]
},
"id": "req-001"
}Error Codes
-32700 Parse error — invalid JSON body
-32600 Invalid request — missing jsonrpc/method/message
-32601 Method not found — unknown action
-32602 Invalid params — missing required fields
References
- A2A Protocol Specification — the official Agent-to-Agent protocol spec
- JSON-RPC 2.0 Specification — the wire format used by A2A
- W3C Verifiable Credentials Data Model v2.0 — credential format used for cert.issue and cert.revoke actions