A condensed overview of the public types, traits, and functions across the
a2a-rust crates.
This page is a curated selection , kept short enough to scan. For the
exhaustive, always-current listing — every item, every signature, generated
from the code on each deploy — see the generated API documentation .
Every name below is checked against the crates by
scripts/check_api_reference.py in CI, so a type that gets renamed cannot leave
a stale entry here. The same script checks the other direction at the crate
roots: every item a crate re-exports from its lib.rs — the names you reach as
use a2a_protocol_types::X — must have a row on this page. Deeper module items
are rustdoc's job.
Module Contents
agent_cardAgent card and capability discovery types artifactArtifact types for the A2A protocol auth_rejectionWhy a request was refused on authentication or authorization grounds errorA2A protocol error types eventsServer-sent event types for A2A streaming extensionsAgent extension and card-signature types failureWhy a task failed, as a class a caller can match on idempotencyClient-supplied idempotency keys for message/send, as a declared extension jsonrpcJSON-RPC 2.0 envelope types messageMessage types for the A2A protocol methodThe A2A v1.0 service methods, mirrored from the ratified specification paramsJSON-RPC method parameter types protoCanonical A2A protobuf message types (lf.a2a.v1) and conversions (proto feature) pushPush notification configuration types responsesRPC method response types securitySecurity scheme types for A2A agent authentication serde_helpersSerialization helpers for reducing allocation overhead signingAgent card signing and verification (spec §10) (signing feature) taskTask types for the A2A protocol trace_contextW3C traceparent / tracestate: parse, validate, derive a child
Constant Description
A2A_VERSIONA2A protocol version string, in the Major.Minor wire form ("1.0") A2A_CONTENT_TYPEThe registered A2A media type (spec §14.1.1), accepted on ingress by the HTTP bindings alongside JSON_CONTENT_TYPE JSON_CONTENT_TYPEContent type emitted by the JSON-RPC and REST bindings (application/json) A2A_VERSION_HEADERHTTP header name for the A2A protocol version (A2A-Version) A2A_EXTENSIONS_HEADERHTTP header name for extension activation (spec §14.2.2) WEBSOCKET_BINDING_URIThis project's identifier for its §12 WebSocket binding, as AgentInterface::protocol_binding
Type Description
TaskUnit of work with ID, status, history, artifacts TaskIdNewtype wrapper for task identifiers TaskStateEnum: Unspecified, Submitted, Working, InputRequired, AuthRequired, Completed, Failed, Canceled, Rejected TaskStatusState + optional message + timestamp TaskVersionMonotonically increasing version number ContextIdConversation context identifier
Type Description
MessageStructured payload with ID, role, parts MessageIdNewtype wrapper for message identifiers MessageRoleEnum: Unspecified, User, Agent PartContent unit: text, raw, url, or data PartContentEnum: Text, Raw, Url, Data FileContentContent of a file part. Deprecated: exists for backward compatibility with v0.3; in v1.0 use Part::raw or Part::url
Type Description
ArtifactResult produced by an agent. Call validate() to check non-empty parts. ArtifactIdNewtype wrapper for artifact identifiers
Type Description
StreamResponseEnum: Task, Message, StatusUpdate, ArtifactUpdate TaskStatusUpdateEventStatus change notification TaskArtifactUpdateEventArtifact delivery notification
Type Description
AgentCardRoot discovery document AgentInterfaceTransport endpoint descriptor AgentCapabilitiesCapability flags (streaming, push, extended card) AgentSkillDiscrete agent capability AgentProviderOrganization info
Type Description
AgentExtensionDescribes an optional extension that an agent supports AgentCardSignatureA cryptographic signature over an AgentCard
Type Description
SecuritySchemeA security scheme supported by an agent NamedSecuritySchemesA map from security scheme name to its definition, as used in AgentCard.securitySchemes SecurityRequirementA security requirement object mapping scheme names to their required scopes StringListA list of strings used within a SecurityRequirement map value ApiKeySecuritySchemeAPI key security scheme: a token sent in a header, query parameter, or cookie ApiKeyLocationWhere an API key is placed in the request HttpAuthSecuritySchemeHTTP authentication security scheme (Bearer, Basic, etc.) OAuth2SecuritySchemeOAuth 2.0 security scheme OAuthFlowsAvailable OAuth 2.0 flows for an OAuth2SecurityScheme AuthorizationCodeFlowOAuth 2.0 authorization code flow ClientCredentialsFlowOAuth 2.0 client credentials flow DeviceCodeFlowOAuth 2.0 device authorization flow (RFC 8628) ImplicitFlowOAuth 2.0 implicit flow (deprecated; retained for compatibility) PasswordOAuthFlowOAuth 2.0 resource owner password credentials flow (deprecated but in spec) OpenIdConnectSecuritySchemeOpenID Connect security scheme MutualTlsSecuritySchemeMutual TLS security scheme
Type Description
MessageSendParamsSendMessage / SendStreamingMessage input SendMessageConfigurationOutput modes, history, push config TaskQueryParamsGetTask input ListTasksParamsListTasks input with filters and pagination CancelTaskParamsCancelTask input TaskIdParamsSubscribeToTask input GetPushConfigParamsGetTaskPushNotificationConfig input DeletePushConfigParamsDeleteTaskPushNotificationConfig input ListPushConfigsParamsListTaskPushNotificationConfigs input GetExtendedAgentCardParamsGetExtendedAgentCard input AcceptedFieldsTrait: the JSON keys a request type accepts, in both protobuf spellings
Type Description
TaskPushNotificationConfigWebhook registration AuthenticationInfoWebhook auth credentials
Type Description
SendMessageResponseEnum: Task or Message TaskListResponsePaginated task list ListPushConfigsResponsePaginated push config list AuthenticatedExtendedCardResponseType alias for AgentCard
Type Description
SerBufferThread-local reusable serialization buffer (2.3x less small-payload overhead) deser_from_strBorrowed deserialization from &str (~15-25% fewer allocations) deser_from_sliceBorrowed deserialization from &[u8] (~15-25% fewer allocations)
Function Description
utc_now_iso8601()Returns the current UTC time as an ISO 8601 string with millisecond precision unix_millis_to_iso8601(millis)Formats Unix-epoch milliseconds as an ISO 8601 UTC string with millisecond precision; pre-epoch clamps to the epoch parse_iso8601_to_unix_millis(s)Parses an ISO 8601 / RFC 3339 timestamp into milliseconds since the Unix epoch; None for anything structurally invalid
Type Description
A2aErrorProtocol-level error ErrorCodeStandard error codes AuthRejectionA refused credential an A2aError carries: its kind and WWW-Authenticate challenge AuthRejectionKindUnauthenticated (HTTP 401, gRPC UNAUTHENTICATED) or PermissionDenied (HTTP 403, gRPC PERMISSION_DENIED)A2aResult<T>Alias for Result<T, A2aError>
Type Description
JsonRpcRequestJSON-RPC 2.0 request envelope JsonRpcErrorJSON-RPC error object JsonRpcVersionVersion marker ("2.0") JsonRpcResponseJSON-RPC 2.0 response: either a success with a result or an error with an error object JsonRpcSuccessResponseA successful JSON-RPC 2.0 response JsonRpcErrorResponseAn error JSON-RPC 2.0 response JsonRpcRequestIdA JSON-RPC 2.0 request identifier with three distinct states JsonRpcIdA JSON-RPC 2.0 response identifier
Module Contents
authAuthentication interceptor and credential storage builderFluent builder for A2aClient clientThe A2aClient itself configClient configuration types discoveryAgent card discovery with HTTP caching errorClient error types interceptorRequest/response interceptor infrastructure methodsPer-method client helpers retryConfigurable retry policy for transient client errors streamingSSE client-side streaming support testingScriptedPeer: a misbehaving agent on any binding (stall, cut-off, mis-frame, 401), for testing a client's failure handling (testing feature)tlsTLS connector via rustls (tls-rustls feature) token_providerToken acquisition: TokenProvider, OAuth 2.0 client-credentials, and OIDC discovery transportTransport abstraction for A2A client requests
Type Description
A2aClientMain client for calling remote agents ClientBuilderFluent builder for client configuration ClientConfigConfiguration for an A2aClient instance EventStreamAsync SSE event stream RetryPolicyConfigurable retry with exponential backoff trace_propagationCarrying W3C trace context on outbound calls CurrentTraceThe trace the current task runs under, and how to start one TracePropagationInterceptorWrites traceparent onto every outbound request ClientErrorErrors that can occur during A2A client operations ClientResult<T>Alias for Result<T, ClientError>
Function Description
resolve_agent_card(base_url)async — fetches the AgentCard from the standard well-known path; no headers, 30 s budgetresolve_agent_card_with_options(base_url, &options)async — the same with the headers and budget in a CardFetchOptions (discovery module; fetch_card_from_url_with_options for an absolute URL)
Method Returns Description
send_message(params)SendMessageResponseSynchronous send stream_message(params)EventStreamStreaming send get_task(params)TaskRetrieve task by ID list_tasks(params)TaskListResponseQuery tasks cancel_task(id)TaskCancel a running task subscribe_to_task(id)EventStreamRe-subscribe to task events subscribe_to_task_from(id, last_event_id)EventStreamResume a broken stream from its last SSE id: (sends Last-Event-ID) set_push_config(config)TaskPushNotificationConfigCreate push config get_push_config(task_id, id)TaskPushNotificationConfigGet push config list_push_configs(params)ListPushConfigsResponseList push configs delete_push_config(task_id, id)()Delete push config get_extended_agent_card()AuthenticatedExtendedCardResponseGet extended card
Type Description
CallInterceptorRequest/response hook trait InterceptorChainOrdered interceptor sequence ClientRequestA logical A2A request as seen by interceptors ClientResponseA logical A2A response as seen by interceptors
Type Description
AuthInterceptorA CallInterceptor that injects Authorization headers from a CredentialsStore CredentialsStorePersistent storage for auth credentials, keyed by session + scheme InMemoryCredentialsStoreAn in-memory CredentialsStore backed by an RwLock<HashMap> SessionIdOpaque identifier for a client authentication session TokenProviderA source of bearer access tokens StaticTokenProviderA TokenProvider that always returns the same fixed token OAuth2ClientCredentialsA TokenProvider implementing the OAuth 2.0 client credentials grant (RFC 6749 §4.4) with caching and proactive refresh BearerAuthInterceptorA CallInterceptor that injects a bearer token from a TokenProvider before every request
Type Description
TransportPluggable transport trait JsonRpcTransportJSON-RPC 2.0 transport RestTransportREST/HTTP transport WebSocketTransportWebSocket transport (websocket feature) WebSocketTransportConfigConfiguration for WebSocketTransport::connect_with_config (websocket feature) GrpcTransportgRPC transport (grpc feature); dials host:port targets and http(s):// URLs GrpcBareAddressSchemeHow a bare host:port gRPC target is dialled: TLS except loopback (default), always TLS, or always plaintext
Module Contents
agent_cardAgent card HTTP handlers (static, dynamic, and caching utilities) authServer-side authentication interceptors builderBuilder for RequestHandler call_contextCall context for server-side interceptors conformanceGrades an AgentExecutor against the protocol invariants (conformance feature) dispatchHTTP dispatch layer — JSON-RPC and REST routing errorServer-specific error types executorAgent executor trait executor_helpersErgonomic helpers for implementing AgentExecutor handlerCore request handler — protocol logic layer interceptorServer-side interceptor chain metricsMetrics hooks for observing handler activity otelOpenTelemetry integration for the A2A server (otel feature) pushPush notification configuration storage and delivery rate_limitFixed-window rate limiter as a ServerInterceptor request_contextRequest context passed to the AgentExecutor serveserve(), serve_with_addr, DispatcherstoreTask storage backend streamingStreaming infrastructure for SSE responses and event queues tenant_configPer-tenant resource limits for multi-tenant A2A servers tenant_resolverTenant resolution for multi-tenant A2A servers
Constant Description
CORS_ALLOW_ALLCORS Access-Control-Allow-Origin header value for public agent cards A2A_VERSION_METADATA_KEYThe service parameter naming the A2A protocol version, spelled the way a non-HTTP binding carries it
Type Description
RequestHandlerCentral protocol orchestrator RequestHandlerBuilderFluent builder for handler configuration RequestContextPer-execution context (task ID, message, etc.) CancellationTokenThe type of RequestContext::cancellation_token, re-exported so an executor need not depend on tokio-util to name it CallContextPer-request metadata (request ID, headers, tenant) HandlerLimitsConfigurable validation limits InboundTracePolicyWhat this handler does with a traceparent an as-yet unauthenticated peer sent (W3C Trace Context §7.2) MIN_MESSAGE_ID_LENGTHThe floor message.id's length bound is never taken below: 36, a hyphenated UUID SendMessageResultResult of RequestHandler::on_send_message: a synchronous response or a streaming reader ShutdownReportWhat a shutdown actually managed to do (live queues it had to destroy, whether executor cleanup completed) InFlightReportWhat RequestHandler::finish_in_flight / cancel_in_flight did: tasks that completed on their own, tasks cancelled, still running at the end of the grace period, whether everything finished ConnectionPoolStatsStatistics about the HTTP connection pool RpcCallOne finished inbound call as Metrics::on_rpc_call reports it: binding, method, duration, status (rpc.server.call.duration)
Trait Description
AgentExecutorAgent logic entry point TaskStoreTask persistence backend PushConfigStorePush config persistence PushSenderWebhook delivery ServerInterceptorServer-side middleware AgentCardProducerDynamic agent card generation DispatcherHTTP dispatch trait (for serve()) MetricsPluggable metrics observer (requests, latency, errors) TenantResolverExtracts tenant from request context RateLimitCounterA request counter every replica shares
Type Description
JsonRpcDispatcherJSON-RPC 2.0 HTTP dispatcher (implements Dispatcher) RestDispatcherRESTful HTTP dispatcher (implements Dispatcher) WebSocketDispatcherWebSocket dispatcher (websocket feature) GrpcDispatchergRPC dispatcher (grpc feature) A2aRouterAxum framework adapter (axum feature)
Name Description
serve(addr, dispatcher) -> io::Result<()>async — binds and drives the accept loop until the future is droppedserve_with_addr(addr, dispatcher) -> io::Result<SocketAddr>async — binds, spawns the accept loop, returns the bound SocketAddr (useful for port-0 in tests)ServerA bound listener that has not started accepting yet; binding is separated from serving so the caller can learn the address ServeConfigLimits applied to a Server ServeReportWhat a shutdown did — Server::serve_with_shutdown, or the gRPC and WebSocket dispatchers' serve_with_shutdown: connections accepted, drained or abandoned, and (with a handler-backed dispatcher) the InFlightReport for its tasks DispatchConfigConfiguration for dispatch-layer limits shared by both JSON-RPC and REST dispatchers GrpcConfigConfiguration for the gRPC dispatcher (grpc feature) validate_version_metadata(metadata, required)Validates the A2A version carried in a binding's request metadata
Name Description
agent_executor!Macro: generates an AgentExecutor implementation from a closure-like syntax boxed_futureWraps an async expression into a pinned, boxed, Send future
Type Description
InMemoryTaskStoreIn-memory task store with TTL InMemoryPushConfigStoreIn-memory push config store HttpPushSenderHTTP webhook delivery with SSRF protection SqliteTaskStoreSQLite task store (sqlite feature) SqlitePushConfigStoreSQLite push config store (sqlite feature) TenantAwareInMemoryTaskStoreMulti-tenant in-memory task store TenantAwareInMemoryPushConfigStoreMulti-tenant in-memory push config store TenantAwareSqliteTaskStoreMulti-tenant SQLite task store (sqlite feature) TenantAwareSqlitePushConfigStoreMulti-tenant SQLite push config store (sqlite feature) PostgresTaskStorePostgreSQL task store (postgres feature) PostgresPushConfigStorePostgreSQL push config store (postgres feature) TenantAwarePostgresTaskStoreMulti-tenant PostgreSQL task store (postgres feature) TenantAwarePostgresPushConfigStoreMulti-tenant PostgreSQL push config store (postgres feature) PgMigrationRunnerPostgreSQL migration runner (postgres feature) StaticAgentCardHandlerStatic agent card with HTTP caching DynamicAgentCardHandlerDynamic agent card with producer HotReloadAgentCardHandlerAgent card with live reloading HeaderTenantResolverTenantResolver that reads a configurable request headerBearerTokenTenantResolverTenantResolver that extracts tenant claims from a JWT bearer tokenPathSegmentTenantResolverTenantResolver that parses tenant from a configurable path segmentRateLimitInterceptorPer-caller rate limiting interceptor PostgresRateLimitCounterA RateLimitCounter backed by a PostgreSQL table (postgres feature) ApiKeyAuthInterceptorRejects requests whose API-key header is absent or not in the allowed set BearerTokenAuthInterceptorRejects requests whose bearer token is absent or not in the allowed set ServerInterceptorChainAn ordered chain of ServerInterceptor instances CallOutcomeHow a call ended — succeeded, failed with the error sent, or cancelled — as ServerInterceptor::on_complete is told MigrationA single SQLite schema migration (sqlite feature) MigrationRunnerRuns schema migrations against a SQLite database (sqlite feature) PgMigrationA single PostgreSQL schema migration (postgres feature) NoopMetricsNo-op metrics implementation (default) OtelMetricsOpenTelemetry metrics (otel feature)
Name Kind Description
EventEmitterstruct Ergonomic event emission helper (wraps an EventQueueWriter) EventQueueWritertrait Write events to a task's event stream EventQueueReadertrait Read events from a task's event stream EventQueueManagerstruct Per-task queue lifecycle manager (create / lookup / destroy) InMemoryQueueWriterstruct Bounded-channel EventQueueWriter implementation InMemoryQueueReaderstruct Bounded-channel EventQueueReader implementation StreamEventstruct One queued event and its position in the task's event log (the SSE id:)
Type Description
CorsConfigCross-origin policy TaskStoreConfigTTL and capacity for in-memory store TenantStoreConfigConfiguration for TenantAwareInMemoryTaskStore TenantContextThread-safe tenant context for scoping store operations PerTenantConfigPer-tenant configuration for timeouts, capacity limits, and executor selection TenantLimitsResource limits declared for a single tenant RateLimitConfigConfiguration for RateLimitInterceptor PushRetryPolicyRetry policy for push notification delivery ServerErrorServer-level error type ServerResult<T>Alias for Result<T, ServerError>
Module Re-exports
a2a_protocol_sdk::typesAll a2a-protocol-types exports a2a_protocol_sdk::clientAll a2a-protocol-client exports a2a_protocol_sdk::serverAll a2a-protocol-server exports a2a_protocol_sdk::preludeMost commonly used types
The prelude includes the most commonly used types from all three crates — see Project Structure for the full list.
use a2a_protocol_sdk::prelude::*;
use a2a_protocol_sdk::types::push::TaskPushNotificationConfig;
fn main() -> Result<(), Box<dyn std::error::Error>> {
let base64_string = "aGVsbG8=";
let card = AgentCard::new("a", "1.0.0", AgentInterface::jsonrpc("http://localhost:3000"));
// Task status
TaskStatus::new(TaskState::Working);
TaskStatus::with_timestamp(TaskState::Completed);
// Messages and parts (v1.0 wire format: flat oneof)
Part::text("hello"); // → {"text": "hello"}
Part::raw(base64_string); // → {"raw": "aGVsbG8="}
Part::url("https://..."); // → {"url": "https://..."}
Part::data(serde_json::json!({"k": 1})); // → {"data": {"k": 1}}
Part::file_bytes(base64_string); // backward-compat alias for raw()
Part::file_uri("https://..."); // backward-compat alias for url()
let wire = |p: Part| serde_json::to_value(p).unwrap();
assert_eq!(wire(Part::text("hello")), serde_json::json!({"text": "hello"}));
assert_eq!(wire(Part::raw(base64_string)), serde_json::json!({"raw": "aGVsbG8="}));
assert_eq!(wire(Part::url("https://...")), serde_json::json!({"url": "https://..."}));
assert_eq!(wire(Part::data(serde_json::json!({"k": 1}))), serde_json::json!({"data": {"k": 1}}));
assert_eq!(wire(Part::file_bytes(base64_string)), wire(Part::raw(base64_string)));
assert_eq!(wire(Part::file_uri("https://...")), wire(Part::url("https://...")));
// Artifacts
Artifact::new("artifact-id", vec![Part::text("content")]);
// IDs
TaskId::new("task-123");
ContextId::new("ctx-456");
MessageId::new("msg-789");
// Capabilities (non_exhaustive — use builder)
AgentCapabilities::none()
.with_streaming(true)
.with_push_notifications(false);
// Agent cards: the three fields `validate` requires, the rest by `with_*`
AgentCard::new("my-agent", "1.0.0", AgentInterface::jsonrpc("http://localhost:3000"))
.with_description("Does one thing well")
.with_skill(AgentSkill::new("echo", "Echo", "Repeats").with_tags(["text"]))
.with_interface(AgentInterface::grpc("http://localhost:50051"))
.with_streaming(true); // one flag; with_capabilities(..) for the rest
// Client-side: which interface `from_card` picked
ClientBuilder::from_card(&card)?.chosen_interface(); // Option<&AgentInterface>
// Push configs
TaskPushNotificationConfig::new("task-id", "https://webhook.url");
Ok(())
}