adk-tool

Tool system for Rust Agent Development Kit (ADK-Rust) agents (FunctionTool, MCP, Google Search).

Overview

adk-tool provides the tool infrastructure for the Rust Agent Development Kit (ADK-Rust):

• FunctionTool - Create tools from async Rust functions
• AgentTool - Use agents as callable tools for composition
• GoogleSearchTool - Web search via Gemini's grounding
• McpToolset - Model Context Protocol integration (local & remote servers)
• BasicToolset - Group multiple tools together
• FilteredToolset - Filter tools from any toolset by predicate
• MergedToolset - Combine multiple toolsets into one
• PrefixedToolset - Namespace tool names with a prefix
• ExitLoopTool - Control flow for loop agents
• LoadArtifactsTool - Inject binary artifacts into context

Installation

[dependencies]
adk-tool = "0.4"

# For remote MCP servers via HTTP:
adk-tool = { version = "0.4", features = ["http-transport"] }

Or use the meta-crate:

[dependencies]
adk-rust = { version = "0.4", features = ["tools"] }

Quick Start

Function Tool

use adk_tool::FunctionTool;
use adk_core::{ToolContext, Result};
use serde_json::{json, Value};
use std::sync::Arc;

async fn get_weather(_ctx: Arc<dyn ToolContext>, args: Value) -> Result<Value> {
    let city = args["city"].as_str().unwrap_or("Unknown");
    Ok(json!({
        "city": city,
        "temperature": 72,
        "condition": "sunny"
    }))
}

let tool = FunctionTool::new(
    "get_weather",
    "Get current weather for a city",
    get_weather,
);

With Parameter Schema (Recommended)

Always add a schema so the LLM knows what parameters to pass:

use schemars::JsonSchema;
use serde::{Deserialize, Serialize};

#[derive(JsonSchema, Serialize, Deserialize)]
struct WeatherParams {
    /// The city to get weather for
    city: String,
}

let tool = FunctionTool::new("get_weather", "Get weather", get_weather)
    .with_parameters_schema::<WeatherParams>();

MCP Tools (Local Server via stdio)

Connect to local MCP servers running as child processes:

use adk_tool::McpToolset;
use rmcp::{ServiceExt, transport::TokioChildProcess};
use tokio::process::Command;

// Connect to a local MCP server
let cmd = Command::new("npx")
    .arg("-y")
    .arg("@modelcontextprotocol/server-filesystem")
    .arg("/path/to/files");

let client = ().serve(TokioChildProcess::new(cmd)?).await?;

let toolset = McpToolset::new(client)
    .with_name("filesystem-tools")
    .with_filter(|name| matches!(name, "read_file" | "write_file"));

// Get cancellation token for graceful shutdown
let cancel_token = toolset.cancellation_token().await;

// ... use toolset with agent ...

// Cleanup before exit
cancel_token.cancel();

MCP Tools (Remote Server via HTTP)

Connect to remote MCP servers using HTTP transport (requires http-transport feature):

use adk_tool::McpHttpClientBuilder;
use std::time::Duration;

// Connect to a public remote MCP server
let toolset = McpHttpClientBuilder::new("https://remote.mcpservers.org/fetch/mcp")
    .timeout(Duration::from_secs(30))
    .connect()
    .await?;

MCP Authentication

Connect to authenticated MCP servers:

use adk_tool::{McpHttpClientBuilder, McpAuth, OAuth2Config};
use std::time::Duration;

// Bearer token (e.g., GitHub Copilot MCP)
let toolset = McpHttpClientBuilder::new("https://api.githubcopilot.com/mcp/")
    .with_auth(McpAuth::bearer(std::env::var("GITHUB_TOKEN")?))
    .timeout(Duration::from_secs(60))
    .connect()
    .await?;

// API key in custom header
let toolset = McpHttpClientBuilder::new("https://mcp.example.com/v1")
    .with_auth(McpAuth::api_key("X-API-Key", "your-api-key"))
    .connect()
    .await?;

// OAuth2 client credentials flow
let oauth_config = OAuth2Config::new(
    "your-client-id",
    "https://auth.example.com/oauth/token"
)
.with_secret("your-client-secret")
.with_scopes(vec!["mcp:read".into(), "mcp:write".into()]);

let toolset = McpHttpClientBuilder::new("https://mcp.example.com/v1")
    .with_auth(McpAuth::oauth2(oauth_config))
    .connect()
    .await?;

MCP Task Support (Long-Running Operations)

Enable async task lifecycle for long-running MCP operations (SEP-1686):

use adk_tool::{McpToolset, McpTaskConfig};
use std::time::Duration;

let toolset = McpToolset::new(client)
    .with_task_support(
        McpTaskConfig::enabled()
            .poll_interval(Duration::from_secs(2))
            .timeout(Duration::from_secs(300))
            .max_poll_attempts(100)
    );

MCP Auto-Reconnect (Connection Resilience)

For long-running agents, use ConnectionRefresher to automatically reconnect when connections fail:

use adk_tool::mcp::{ConnectionRefresher, ConnectionFactory, RefreshConfig};
use rmcp::{RoleClient, ServiceExt, service::RunningService, transport::TokioChildProcess};
use std::sync::Arc;
use tokio::process::Command;

// Define a factory that can create new connections
struct MyConnectionFactory {
    command: String,
    args: Vec<String>,
}

#[async_trait::async_trait]
impl<S> ConnectionFactory<S> for MyConnectionFactory
where
    S: rmcp::service::Service<RoleClient> + Send + Sync + 'static,
{
    async fn create_connection(&self) -> Result<RunningService<RoleClient, S>, String> {
        let cmd = Command::new(&self.command)
            .args(&self.args)
            .spawn()
            .map_err(|e| e.to_string())?;
        
        ().serve(TokioChildProcess::new(cmd).map_err(|e| e.to_string())?)
            .await
            .map_err(|e| e.to_string())
    }
}

// Create initial connection
let cmd = Command::new("npx")
    .arg("-y")
    .arg("@modelcontextprotocol/server-filesystem")
    .arg("/path/to/files");
let client = ().serve(TokioChildProcess::new(cmd)?).await?;

// Wrap with auto-reconnect
let factory = Arc::new(MyConnectionFactory {
    command: "npx".to_string(),
    args: vec!["-y".into(), "@modelcontextprotocol/server-filesystem".into(), "/path".into()],
});

let refresher = ConnectionRefresher::new(client, factory)
    .with_config(RefreshConfig::default()
        .with_max_attempts(5)
        .with_retry_delay_ms(2000));

// Operations automatically retry on connection failure
let tools = refresher.list_tools().await?;
if tools.reconnected {
    println!("Connection was refreshed during operation");
}

The refresher handles these error conditions automatically:

• Connection closed / EOF
• Broken pipe / transport errors
• Session not found (server restart)
• Connection reset

Google Search

use adk_tool::GoogleSearchTool;

let search = GoogleSearchTool::new();
// Add to agent - enables grounded web search

Features

MCP Server Examples

Available Public MCP Servers

• https://remote.mcpservers.org/fetch/mcp - Web content fetching
• https://remote.mcpservers.org/sequentialthinking/mcp - Step-by-step reasoning

GitHub Copilot MCP (40+ tools)

// Requires GITHUB_TOKEN with Copilot access
let toolset = McpHttpClientBuilder::new("https://api.githubcopilot.com/mcp/")
    .with_auth(McpAuth::bearer(std::env::var("GITHUB_TOKEN")?))
    .connect()
    .await?;

// Discovered tools include:
// - search_repositories, search_code, search_issues
// - create_pull_request, merge_pull_request
// - get_file_contents, create_or_update_file
// - issue_read, issue_write, add_issue_comment
// - and 30+ more GitHub operations

Toolset Composition

Compose, filter, and namespace toolsets for complex agent configurations:

use adk_tool::{BasicToolset, FilteredToolset, MergedToolset, PrefixedToolset, string_predicate};
use std::sync::Arc;

// Group tools into named toolsets
let weather = Arc::new(BasicToolset::new("weather", vec![get_weather, get_forecast]));
let utils = Arc::new(BasicToolset::new("utils", vec![search, calculate]));

// Filter: expose only specific tools from a toolset
let filtered = FilteredToolset::new(weather.clone(), string_predicate(vec!["get_weather".into()]));

// Or use a custom predicate
let custom = FilteredToolset::with_name(
    weather.clone(),
    Box::new(|tool| tool.name().starts_with("get_")),
    "get_only",
);

// Merge: combine multiple toolsets (first-wins deduplication)
let merged = MergedToolset::new("all_tools", vec![weather.clone(), utils.clone()]);

// Prefix: namespace tool names to avoid collisions
let prefixed = PrefixedToolset::new(weather.clone(), "wx"); // wx_get_weather, wx_get_forecast

// Chain them: prefix → filter → merge
let composed = MergedToolset::new("composed", vec![
    Arc::new(PrefixedToolset::new(weather, "wx")) as Arc<dyn Toolset>,
    Arc::new(FilteredToolset::new(utils, string_predicate(vec!["search".into()]))),
]);

// Register with an agent
let agent = LlmAgentBuilder::new("agent")
    .model(model)
    .toolset(Arc::new(composed))
    .build()?;

All composition utilities implement Toolset and work with any Toolset implementation including McpToolset and BrowserToolset.

Migration from rmcp 0.9

No changes required! The rmcp 0.14 breaking changes were handled internally:

Your existing code using McpToolset::new(client) continues to work unchanged.

Related Crates

• adk-rust - Meta-crate with all components
• adk-core - Core Tool trait
• adk-agent - Agents that use tools

License

Apache-2.0

Part of ADK-Rust

This crate is part of the ADK-Rust framework for building AI agents in Rust.