langgraph-rust

A Rust implementation of LangGraph -- a framework for building stateful, multi-actor applications with LLMs.

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Table of Contents

• Overview
• Projects Built with langgraph-rust
• Project Structure
• Quick Start
• Supported Providers
• Supported Checkpointers
• Roadmap
• Examples
• Crate Overview
• Requirements
• License

Overview

langgraph-rust brings the core LangGraph concepts into idiomatic Rust:

• StateGraph -- Directed graphs where nodes are async functions that transform state, and edges define control flow
• Pregel Engine -- Bulk Synchronous Parallel (BSP) execution: Plan -> Execute (parallel via tokio) -> Update
• Channels -- Type-erased state containers with reducers, fan-in barriers, and pub-sub semantics
• Checkpointing -- Full state persistence for pause/resume, human-in-the-loop, and time-travel debugging. Supports InMemory, Postgres, and SQLite.
• Tracing & Observability -- Real-time tracing server and UI for visualizing graph execution and LLM calls.
• ReAct Agent -- Prebuilt Reasoning + Acting agent pattern with tool execution.
• OpenAI Provider -- Integration with OpenAI-compatible APIs (GPT-4o, Ollama, vLLM, DeepSeek, etc.).

Projects Built with langgraph-rust

• flock - A multi-agent framework built on top of langgraph-rust.

Project Structure

langgraph-rust/
├── crates/
│   ├── langgraph/                 # Core engine: StateGraph, Pregel BSP, Channels, Streaming
│   ├── langgraph-derive/          # Proc macros: #[derive(StateGraph)], #[tool], #[derive(Traceable)]
│   ├── langgraph-prebuilt/        # Prebuilt components: ReAct agent, ToolNode, Messages
│   ├── langgraph-checkpoint/      # Checkpointer traits and InMemorySaver
│   ├── langgraph-checkpoint-postgres/  # Postgres persistence via sqlx
│   ├── langgraph-checkpoint-sqlite/    # SQLite persistence via sqlx
│   ├── langgraph-tracing/         # Real-time tracing server and observability
│   ├── langgraph-providers/       # LLM integrations: OpenAI, OpenAI-compatible
│   └── langgraph-prebuilt/        # Prebuilt agents and nodes
└── examples/                      # 16 runnable examples covering all features

Quick Start

Installation

Add langgraph to your Cargo.toml:

[dependencies]
# Basic core package
langgraph = "0.2.0"

# Or enable optional features out-of-the-box:
# langgraph = { version = "0.2.0", features = ["prebuilt", "providers", "sqlite"] }

Cargo Features

The langgraph umbrella crate organizes the ecosystem into separate cargo features:

• prebuilt: ReAct agent, ToolNode, message types, and base chat model trait.
• providers: Model providers integration (OpenAI, compatibility clients).
• tracing: Tracing server, observer, and telemetry.
• sqlite: SQLite checkpointer persistence.
• postgres: PostgreSQL checkpointer persistence.

Configure Environment

Copy .env.example to .env and fill in your specific model information:

cp .env.example .env

Example .env content:

OPENAI_API_KEY=sk-xxxxxxxxxxxxxxxxxxxxxx
OPENAI_API_BASE=https://xxxxxxx/v1
OPENAI_MODEL=xxxxxxx

Define a ReAct Agent with Tools

use langgraph_derive::tool;
use langgraph_prebuilt::{create_react_agent, prepare_tools, ReActAgentConfig};
use langgraph_providers::openai::{OpenAIModel, OpenAIModelConfig};
use langgraph_checkpoint::config::RunnableConfig;
use std::sync::Arc;

// Define tools with the #[tool] macro
#[tool("get_weather", "Get the current weather for a given location.")]
fn get_weather(location: String) -> Result<String, String> {
    Ok(format!("Weather for {}: sunny, 22°C", location))
}

#[tool("calculator", "Evaluate a mathematical expression.")]
fn calculator(expression: String) -> Result<String, String> {
    Ok(format!("{} = 42", expression))
}

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Prepare tools
    let prepared = prepare_tools(vec![
        Arc::new(GetWeather::new()),
        Arc::new(Calculator::new()),
    ]);

    // Create LLM
    let model = OpenAIModel::new(OpenAIModelConfig {
        model: "gpt-4o".to_string(),
        api_key: std::env::var("OPENAI_API_KEY")?,
        api_base: None,
        temperature: Some(0.7),
        ..Default::default()
    });

    // Build ReAct agent
    let agent = create_react_agent(
        Arc::new(model),
        prepared.tools,
        Some(ReActAgentConfig {
            system_prompt: Some("You are a helpful assistant.".to_string()),
            max_steps: Some(10),
            handle_tool_errors: true,
        }),
    )?;

    // Invoke
    let input = serde_json::json!({
        "messages": [{"type": "human", "content": "What's the weather in Beijing?"}]
    });
    let result = agent.ainvoke(&input, &RunnableConfig::new()).await?;
    println!("{:#?}", result);

    Ok(())
}

Build a Custom StateGraph

use langgraph::prelude::*;
use langgraph_derive::langgraph_state;
use langgraph::channels::binop::append_reducer;

#[langgraph_state]
#[derive(Debug)]
struct MyState {
    #[channel(reducer = "append_reducer")]
    steps: Vec<String>,
    result: String,
}

// Build graph: START -> process -> validate -> END
let channels = MyState::create_channels();
let mut graph = StateGraph::new(channels);

graph.add_node("process", node_fn!(|input, _config| {
    Ok(serde_json::json!({
        "steps": vec!["processed"],
        "result": "done"
    }))
}))?;

graph.add_node("validate", node_fn!(|input, _config| {
    Ok(serde_json::json!({
        "steps": vec!["validated"]
    }))
}))?;

graph.add_edge(START, "process")?;
graph.add_edge("process", "validate")?;
graph.add_edge("validate", END)?;
let app = graph.compile()?;

Human-in-the-Loop

use langgraph::types::{interrupt, Command};

// In a node function:
fn approval_node(state: &MyState) -> MyState {
    let human_response = interrupt("Please review and approve");
    // Execution pauses here, resumes when Command::resume is provided
    state.clone()
}

// Resume execution:
compiled_graph.update_state(
    &config,
    &Command::resume("approved".into()),
);

Supported Providers

Supported Checkpointers

Roadmap

Providers

• Anthropic (Claude)
• DeepSeek
• Google Gemini
• Qwen
• Zhipu

Checkpointers

• SQLite Checkpointer
• Redis Checkpointer

Features

• Subgraph support
• More prebuilt agent patterns

Examples

Run an example:

# Set your API key
export OPENAI_API_KEY=sk-xxx
# Optional: custom base URL for Ollama/vLLM
# export OPENAI_API_BASE=http://localhost:11434/v1

cargo run --example react_agent
cargo run --example interactive_chat
cargo run --example interactive_chat_with_tracing
cargo run --example human_in_the_loop
cargo run --example sqlite_checkpoint

Crate Overview

Requirements

• Rust >= 1.75
• Tokio runtime (full features)

License

MIT