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A2A (Agent-to-Agent) lets you expose an agent as a standards-compliant HTTP server or connect remote A2A agents as tool providers for your LLM.

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A2A server

Any agent can be exposed as an A2A HTTP server. Call RunA2A(ctx) after NewAgent — the server blocks until the context is cancelled, then shuts down gracefully. Endpoints:
RoutePurpose
GET /.well-known/agent-card.jsonAgent card — name, description, skills, streaming capability, supported auth schemes
POST /JSON-RPC v2 only — SendMessage, SendStreamingMessage, GetTask, etc.
The server accepts JSON-RPC v2 only (PascalCase methods: SendMessage, SendStreamingMessage, GetTask). Legacy slash-style method strings and HTTP REST paths are not supported.
a, err := agent.NewAgent(
    agent.WithName("my-agent"),
    agent.WithDescription("Helpful assistant exposed as an A2A server."),
    agent.WithLLMClient(llmClient),
    agent.WithStream(true),           // advertises streaming capability in agent card
    agent.WithA2ADefaultServer(),     // binds to localhost:9999, no auth
)
if err != nil {
    return err
}
defer a.Close()

ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
defer stop()

if err := a.RunA2A(ctx); err != nil {
    log.Fatal(err)
}

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Custom server config

agent.WithA2AServer(&agent.A2AServerConfig{
    Hostname:     "0.0.0.0",
    Port:         8080,
    BearerTokens: []string{os.Getenv("A2A_SERVER_TOKEN")},
    AgentCard:    &interfaces.A2AAgentCard{ /* optional overrides */ },
})
FieldDefaultDescription
HostnamelocalhostBind address — use 0.0.0.0 for external connections
Port9999TCP port
BearerTokensempty (no auth)Static pre-shared bearer tokens — enforced on every inbound call. The agent card endpoint stays public
AgentCardauto-generatedOverride card fields — merged with agent name, tools, and listen URL
Currently supported auth scheme: static bearer token. OAuth 2.0 / OIDC, API key, and mTLS are planned but not yet implemented.
See A2A Server example.

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A2A client

Remote A2A agents connect as tool providers. The SDK resolves the agent card, discovers skills, and registers each skill as a tool (a2a_<server>_<skillId>). Failing fast if a server is unreachable at NewAgent.

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WithA2AConfig

import a2apkg "github.com/agenticenv/agent-sdk-go/pkg/a2a"

a, err := agent.NewAgent(
    agent.WithLLMClient(llmClient),
    agent.WithA2AConfig(agent.A2AServers{
        "assistant": {
            URL:     "https://assistant.example.com",
            Timeout: 30 * time.Second,
        },
        "researcher": {
            URL:         "https://researcher.example.com",
            Token:       os.Getenv("A2A_TOKEN"),
            SkillFilter: a2apkg.A2ASkillFilter{AllowSkills: []string{"search", "summarize"}},
            Timeout:     60 * time.Second,
        },
    }),
)

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WithA2AClients

import a2aclient "github.com/agenticenv/agent-sdk-go/pkg/a2a/client"

cl, err := a2aclient.NewClient("assistant", "https://assistant.example.com",
    a2aclient.WithTimeout(30*time.Second),
    a2aclient.WithToken(os.Getenv("A2A_TOKEN")),
)
if err != nil {
    return err
}

a, err := agent.NewAgent(
    agent.WithLLMClient(llmClient),
    agent.WithA2AClients(cl),
)
SkipTLSVerify is available on client config for local HTTPS development only — avoid using it in production.

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Runtime changes

Add or remove A2A agents after NewAgent via a.A2ARegistry() — skills are re-discovered on each run.

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Examples

A2A Server

Inbound agent card and JSON-RPC

A2A Config

Outbound WithA2AConfig

A2A Client

Outbound WithA2AClients

Sub-agents

In-process specialist delegation

Approvals

A2A skills follow the same approval policy

Streaming

A2A streaming via SendStreamingMessage

Configuration

WithA2AConfig, WithA2AServer, WithA2AClients