ADK MCP SDK

The shared contract between MCP servers and the ADK-Rust Enterprise registry. Every server in the ecosystem implements these traits to enable automatic onboarding, health monitoring, tool governance, and risk classification.

Architecture

What This Crate Provides

Installation

[dependencies]
adk-mcp-sdk = "0.2"

Quick Start

1. Implement HealthCheck

use adk_mcp_sdk::{HealthCheck, HealthStatus};

#[derive(Clone)]
struct MyServer;

#[async_trait::async_trait]
impl HealthCheck for MyServer {
    async fn check_health(&self) -> HealthStatus {
        // Check your backend connectivity, auth, schema, etc.
        HealthStatus {
            healthy: true,
            message: Some("All systems operational".into()),
            latency_ms: Some(5),
        }
    }
}

2. Create mcp-server.toml

server_id = "mcp_my_server"
display_name = "My MCP Server"
version = "0.2.0"
domain = "platform"
sdk_version = "0.2.0"
risk_level = "medium"
writes_allowed = "gated"
transports = ["stdio"]
credentials = ["vault://my-api-key"]
governance_gates = []
environments = ["development", "staging", "production"]

[[tools]]
name = "list_items"
description = "List items with optional filters"
risk_class = "read_only"
requires_approval = false
credential_bindings = []

[[tools]]
name = "create_item"
description = "Create a new item (gated write)"
risk_class = "internal_write"
requires_approval = true
credential_bindings = ["vault://my-api-key"]

3. Load and Validate Manifest

use adk_mcp_sdk::ServerManifest;
use std::path::Path;

// Load and validate on startup
let manifest = ServerManifest::from_file(Path::new("mcp-server.toml"))?;
let errors = manifest.validate();
if !errors.is_empty() {
    for e in &errors {
        eprintln!("manifest error: {e}");
    }
    std::process::exit(1);
}

// From string
let manifest = ServerManifest::from_toml(include_str!("../mcp-server.toml"))?;

// Programmatic
let manifest = ServerManifest {
    server_id: "mcp_my_server".into(),
    display_name: "My MCP Server".into(),
    version: env!("CARGO_PKG_VERSION").into(),
    domain: "platform".into(),
    transports: vec![adk_mcp_sdk::manifest::Transport::Stdio],
    risk_level: adk_mcp_sdk::risk::RiskLevel::Medium,
    writes_allowed: adk_mcp_sdk::manifest::WritesAllowed::Gated,
    sdk_version: "0.2.0".into(),
    tools: vec![],
    credentials: vec![],
    governance_gates: vec![],
    environments: vec!["development".into(), "production".into()],
};

4. Declare Tool Metadata

use adk_mcp_sdk::{RiskClass, ToolMeta};

let tools = vec![
    ToolMeta {
        name: "search_items".into(),
        description: "Search items by query".into(),
        risk_class: RiskClass::ReadOnly,
        requires_approval: false,
        credential_bindings: vec![],
    },
    ToolMeta {
        name: "delete_item".into(),
        description: "Delete an item permanently".into(),
        risk_class: RiskClass::ExternalWrite,
        requires_approval: true,
        credential_bindings: vec!["vault://admin-key".into()],
    },
];

Risk Classes

The governance engine uses risk classes to determine approval requirements, audit depth, and environment restrictions.

Risk Levels (Server-Level)

Server Manifest Reference

Complete Example: Building an MCP Server

use adk_mcp_sdk::{HealthCheck, HealthStatus};
use rmcp::{handler::server::wrapper::Parameters, schemars, tool, tool_router, ServiceExt, transport::stdio};

#[derive(Debug, serde::Deserialize, schemars::JsonSchema)]
pub struct SearchInput {
    pub query: String,
    #[serde(default = "default_limit")]
    pub limit: u32,
}
fn default_limit() -> u32 { 20 }

#[derive(Clone)]
pub struct MyServer;

#[tool_router]
impl MyServer {
    #[tool(description = "Search items by query")]
    async fn search(&self, Parameters(input): Parameters<SearchInput>) -> String {
        format!("Found results for '{}' (limit {})", input.query, input.limit)
    }
}

adk_mcp_sdk::mcp_2026_server! {
    server: MyServer,
    task_tools: ["search"],
    approval_tools: [],
    cache_ttl_ms: 60_000,
}

#[async_trait::async_trait]
impl HealthCheck for MyServer {
    async fn check_health(&self) -> HealthStatus {
        HealthStatus { healthy: true, message: None, latency_ms: Some(1) }
    }
}

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    tracing_subscriber::fmt().with_env_filter("info").init();
    let service = MyServer.serve(stdio()).await?;
    service.waiting().await?;
    Ok(())
}

MCP 2026-07-28 runtime contract

SDK 0.2 provides a shared handler for the new stateless protocol while retaining legacy initialization for MCP 2025-11-25 clients:

• Per-request protocol, client identity, and capability metadata are read from _meta by rmcp. Protected calls require a non-empty client identity.
• Selected operations are returned as SEP-2663 Tasks when the client advertises Tasks. Clients can get, update, and cancel those tasks.
• Manifest-gated tools use SEP-2322 MRTR elicitation. The approval state is HMAC-protected, bound to the caller, tool, and arguments, and expires after two minutes. Legacy clients fail closed for protected tools.
• Tool lists carry SEP-2549 ttlMs and public cache scope. rmcp removes these fields automatically for legacy responses.
• Ordinary legacy tool calls continue to work after the initialize handshake.

Set MCP_REQUEST_STATE_KEY to at least 32 high-entropy bytes on every instance that can receive a retry. All instances in a deployment must share the same key so an MRTR flow can resume on any replica. Task storage is process-local in this release; route task follow-ups to the creating instance or replace the manager with a durable store before scale-to-zero deployment.

The minimum supported Rust version is 1.94.1. CI should test both MCP 2025-11-25 and 2026-07-28 behavior, including an ordinary legacy call, task lifecycle, approval rejection/tamper handling, and cache-hint serialization.

Servers Using This SDK

Creating a New Server

# Clone the template
git clone https://github.com/zavora-ai/mcp-server-template my-server
cd my-server

# Edit Cargo.toml — rename package, update description
# Edit mcp-server.toml — set server_id, tools, risk level
# Edit src/main.rs — implement your tools

# Build and test
cargo build
cargo test

# Publish
cargo publish

The template includes a working #[tool_router(server_handler)] example with HealthCheck, tracing, and stdio transport.

Integration with rmcp

This SDK provides metadata and governance — it does not replace rmcp which provides the MCP protocol transport. A typical server uses both:

[dependencies]
adk-mcp-sdk = "0.2"                    # Registry and MCP 2026 runtime contract
rmcp = { version = "1.7", features = ["server", "transport-io", "macros"] }  # MCP protocol

• rmcp handles: tool routing, JSON-RPC, stdio/HTTP transport, schema generation
• adk-mcp-sdk handles: health monitoring, manifest declaration, risk classification, credential binding

Documentation

Contributing

1. Fork the repository
2. Create a feature branch (git checkout -b feat/my-feature)
3. Implement with tests
4. Submit a pull request

Contributors

License

Apache-2.0 — see LICENSE for details.

Part of the ADK-Rust Enterprise MCP server ecosystem.

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