A2A Rust SDK

a2a-rs is a Rust workspace for the A2A v1 protocol. It includes core protocol types, async client and server libraries, protobuf definitions, and gRPC bindings for building interoperable A2A agents and clients.

The workspace supports:

• JSON-RPC 2.0 over HTTP
• REST / HTTP+JSON
• gRPC via tonic
• SLIMRPC via slim_bindings
• Server-Sent Events for streaming responses
• Protobuf-based interop with other SDKs and runtimes

Workspace

Crate	Purpose
a2a	Core A2A types, errors, events, JSON-RPC types, and wire-compatible serde behavior
a2a-client	Async A2A client with transport abstraction and protocol negotiation from agent cards
a2a-server	Async server framework with REST and JSON-RPC bindings built on axum
a2a-pb	Protobuf schema, generated types, ProtoJSON-capable generated types, and native <-> protobuf conversion helpers
a2a-grpc	gRPC client and server bindings built on tonic
a2a-slimrpc	SLIMRPC client and server bindings built on slim_bindings
a2acli	Standalone A2A client CLI, published as agntcy-a2acli, for inspecting agent cards, sending messages, managing tasks, and handling push configs
examples/helloworld	Minimal runnable example agent

Supported Bindings

Binding	Client	Server
JSON-RPC	a2a-client	a2a-server
HTTP+JSON / REST	a2a-client	a2a-server
gRPC	a2a-grpc	a2a-grpc
SLIMRPC	a2a-slimrpc	a2a-slimrpc

The gRPC support uses the schema in a2a-pb/proto/a2a.proto. The REST and JSON-RPC bindings are intended to stay wire-compatible with other A2A SDKs, including Go and C# implementations.

Requirements

• Rust 1.85 or newer
• A stable rustup toolchain is recommended
• just is optional but useful for common development commands
• cargo-llvm-cov is optional if you want HTML coverage reports

Build And Test

cargo build --workspace
cargo test --workspace

Common project commands are also available through just:

just build
just test
just lint
just fmt-check
just ci

Coverage

Install cargo-llvm-cov once:

cargo install cargo-llvm-cov

Then run:

just coverage

This writes the HTML report to target/llvm-cov/html/index.html.

Running The Example Agent

The hello world example exposes an echo-style agent over REST and JSON-RPC.

cargo run -p helloworld

When the example starts, the following endpoints are available:

• Agent card: http://localhost:3000/.well-known/agent-card.json
• JSON-RPC endpoint: http://localhost:3000/jsonrpc
• REST endpoint: http://localhost:3000/rest

The example does not start a gRPC server, but the a2a-grpc crate provides the client and server bindings needed to add one.

Running The A2A CLI

The workspace includes a standalone CLI client built on a2a-client. It resolves the public agent card from a base URL, negotiates JSON-RPC or HTTP+JSON, prints responses as JSON, and manages task push notification configs.

cargo run --bin a2acli -- card
cargo run --bin a2acli -- send "hello from rust"
cargo run --bin a2acli -- stream "hello from rust"
cargo run --bin a2acli -- list-tasks
cargo run --bin a2acli -- push-config list task-123

By default the CLI targets http://localhost:3000, which matches the bundled hello world server. Override the target with --base-url https://host for any compatible A2A server, use --binding jsonrpc or --binding http-json to pin transport selection, and pass --bearer-token or repeated --header Name:Value arguments when the server requires authentication.

Install from the workspace with cargo install --path a2acli, or from crates.io after release with cargo install agntcy-a2acli.

Depending On The Workspace

Until the crates are published, depend on them directly from Git:

[dependencies]
a2a = { package = "agntcy-a2a", git = "https://github.com/agntcy/a2a-rs.git" }
a2a-client = { package = "agntcy-a2a-client", git = "https://github.com/agntcy/a2a-rs.git" }
a2a-server = { package = "agntcy-a2a-server", git = "https://github.com/agntcy/a2a-rs.git" }
a2a-pb = { package = "agntcy-a2a-pb", git = "https://github.com/agntcy/a2a-rs.git" }
a2a-grpc = { package = "agntcy-a2a-grpc", git = "https://github.com/agntcy/a2a-rs.git" }
a2a-slimrpc = { package = "agntcy-a2a-slimrpc", git = "https://github.com/agntcy/a2a-rs.git" }

Typical usage is:

• a2a for protocol types and serde models
• a2a-client for clients that negotiate REST or JSON-RPC from an agent card
• a2a-server for agent implementations on axum
• a2a-grpc when you need gRPC transport support
• a2a-slimrpc when you need SLIMRPC transport support
• a2a-pb when you need direct access to protobuf messages or conversion helpers

Repository Layout

• a2a/: core protocol crate
• a2a-client/: client transports and factory
• a2a-server/: request handler, routers, streaming, and stores
• a2a-pb/: protobuf schema and conversion layer
• a2a-grpc/: tonic-based bindings
• a2a-slimrpc/: SLIMRPC bindings
• a2acli/: standalone A2A client CLI and published binary package
• examples/helloworld/: runnable sample agent

Contributing

See CONTRIBUTING.md for contribution guidelines, SECURITY.md for security reporting, and CODE_OF_CONDUCT.md for community expectations.

License

Apache-2.0. See LICENSE.md.