Relay

An async-first Rust framework for building agentic AI systems.

Features

• Provider-agnostic — swap OpenAI, Anthropic, or any custom LLM without changing agent logic
• Type-safe tools — implement Tool with typed Input/Output, or use the #[tool] macro
• ReAct loop — built-in reason-act-observe agent with configurable guardrails
• Streaming — SSE streaming support for both OpenAI and Anthropic
• Composable — agents, tools, and memory backends are all trait-based and swappable
• Async-first — built on Tokio with zero blocking I/O

Workspace

Crate	Description
relay-core	Traits, types, error types — no I/O
relay-providers	OpenAI and Anthropic adapters + mock
relay-agents	ReAct reasoning loop and AgentBuilder
relay-tools	Built-in tools: calculator, datetime, HTTP
relay-memory	In-memory key-value and episodic memory
relay-macros	#[tool] proc macro
relay-workflow	Multi-agent orchestration (WIP)
relay	Unified re-export crate

Quick Start

[dependencies]
relay = { path = "relay", features = ["openai"] }

use relay::prelude::*;
use relay::AgentBuilder;
use relay_providers::openai::OpenAiProvider;
use relay_tools::CalculatorTool;

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    dotenvy::dotenv().ok();

    let agent = AgentBuilder::new()
        .name("assistant")
        .system_prompt("You are a helpful assistant.")
        .provider(OpenAiProvider::from_env()?)
        .tool(CalculatorTool)
        .build()?;

    let output = agent.run("What is 15 * 23?").await?;
    println!("{}", output.answer.unwrap_or_default());
    Ok(())
}

Running Examples

Add your API key to a .env file at the workspace root:

OPENAI_API_KEY=sk-...
# ANTHROPIC_API_KEY=sk-ant-...

# openai (default)
cargo run --example live_agent --all-features

# anthropic
cargo run --example live_agent --all-features -- --provider anthropic

# custom prompt
cargo run --example live_agent --all-features -- "What day is it today?"

# mock provider (no key needed)
cargo run --example basic_agent

Running Tests

cargo test --all-features

License

MIT OR Apache-2.0