Dart developers do not need a Python or Node.js service just to experiment with agents and Model Context Protocol (MCP) tools. This project uses adk_dart
for the agent and shelf
for a small HTTP server that exposes an MCP-compatible greeting tool over Server-Sent Events (SSE).
The complete code is in the adk-hello-world-dart repository.
Note- the Dart library is not an official ADK. An official Dart ADK has not been released as of July 2026. This approach provides an alternative to start working with agents in Dart without waiting for an official SDK.
The repository has two related examples:
bin/main.dart
creates an LlmAgent
and registers an ADK FunctionTool
.bin/server.dart
starts a Shelf server with an SSE endpoint and a JSON-RPC message endpoint.The server implements the MCP methods needed by this demo: initialize
, notifications/initialized
, ping
, tools/list
, and tools/call
. The transport and JSON-RPC routing are deliberately small and live in SessionService
; they are not a general-purpose MCP server implementation.
flowchart LR
Client[MCP client] -->|GET /sse| Server[Shelf server]
Server -->|endpoint event| Client
Client -->|POST /messages?sessionId=...| Server
Server --> Session[SessionService]
Session --> Tool[greet tool]
CLI[Dart CLI] --> Agent[ADK LlmAgent]
Agent --> ADKTool[ADK FunctionTool]
The current project targets Dart 3.5 or later and uses these package versions:
environment:
sdk: ^3.5.0
dependencies:
adk_dart: ^2026.7.24
adk_mcp: ^2026.7.24
logging: ^1.3.0
shelf: ^1.4.1
shelf_router: ^1.1.4
uuid: ^4.5.1
Install them with:
dart pub get
adk_dart
is used directly by the sample agent. The repository also tracks adk_mcp
, while the current server keeps its MCP transport explicit in SessionService
so the protocol flow is easy to inspect.
The project keeps the greeting logic separate from its ADK and MCP wrappers:
class Tools {
static String formatGreeting(String name) {
return 'Hello, $name!';
}
static final FunctionTool greetFunctionTool = FunctionTool(
name: Config.toolGreet,
description: 'Get a greeting from a local HTTPS server.',
func: ({String? param}) {
final name = param ?? 'World';
return formatGreeting(name);
},
);
}
Tools
also exposes an MCP tool definition with a JSON Schema input named param
. Keeping formatGreeting
as a plain Dart function makes the domain behavior easy to unit test.
AdkGreetingAgent
attaches the function tool to an LlmAgent
:
class AdkGreetingAgent {
static LlmAgent createAgent() {
return LlmAgent(
name: 'GreetingAgent',
description: 'An AI Agent built with adk_dart that provides greetings.',
instruction:
'You are a friendly greeting assistant. '
'Use the greet tool to provide personalized greetings.',
tools: [Tools.greetFunctionTool],
);
}
}
Run the CLI example to confirm that the agent and tool can be created:
dart run bin/main.dart
This command initializes the agent and prints a sample tool result. It does not call a hosted model.
The Shelf server registers four routes:
router.get('/', (request) => Response.ok('ADK & MCP Dart Server Running'));
router.get('/health', (request) => Response.ok('OK'));
router.get(Config.sseEndpoint, sessionService.handleSseSession);
router.post(Config.messagesEndpoint, sessionService.handlePostMessage);
When a client opens GET /sse
, SessionService
creates an in-memory session and sends an endpoint
event containing a URL such as:
/messages?sessionId=7c6d...
The client posts JSON-RPC requests to that URL. Responses arrive as message
events on the original SSE connection.
Start the server with:
dart run bin/server.dart
It listens on port 8080
by default. Set the PORT
environment variable to use another port.
For an MCP client that supports remote SSE servers, point it at:
http://localhost:8080/sse
A typical client configuration looks like this:
{
"mcpServers": {
"dart-greeting-server": {
"url": "http://localhost:8080/sse"
}
}
}
Configuration keys differ between MCP clients, so check the documentation for the client you use. Once connected, call the greet
tool with:
{
"param": "Dart developer"
}
The result is Hello, Dart developer!
.
The repository includes unit tests for the greeting behavior and endpoint tests for the Shelf server:
dart test
dart analyze
You can run the complete build, analysis, and test sequence with:
make check
The included multi-stage Dockerfile compiles the server to a native executable and copies it into a small scratch image:
docker build -t adk-hello-world-dart .
docker run --rm -p 8080:8080 adk-hello-world-dart
Check the running container at http://localhost:8080/health
.
cloudbuild.yaml
builds the image, pushes it to Container Registry, and deploys the service in us-central1
:
make deploy
The deployment allows unauthenticated access and sets --max-instances 1
.
That instance limit matters here. Active SSE transports are stored in a process-local map, so a POST request routed to another instance would not find its session. A production service should move session state to shared storage or use a transport and deployment design that does not depend on process-local routing. Authentication, origin restrictions, request validation, timeouts, and rate limiting would also need attention before exposing the service publicly.
This sample is intentionally narrow: one agent, one deterministic tool, and enough MCP handling to show the request flow. Useful next steps include replacing the greeting with real domain logic, using adk_mcp
transport primitives as the Dart package evolves, adding model configuration to execute the agent, and moving session state out of memory before scaling the service.
Resources: