rig

Rig

Rig (crate rig-core) is a Rust library for building LLM-powered applications: provider clients, agents with tools, structured extractors, RAG pipelines, and streaming completions. This skill covers rig-core 0.40.0, workspace edition 2024, repo-pinned toolchain 1.94.0.

Setup

cargo add rig-core

Feature flags relevant to agent work:

• derive — enables the rig-derive macros (schema derivation for tool/extractor types)
• rmcp — enables MCP (Model Context Protocol) tool integration via the rmcp crate

[dependencies]
rig-core = { version = "0.40", features = ["rmcp"] }

derive and reqwest/rustls ship in rig-core's default feature set; add rmcp explicitly for MCP tools.

AgentBuilder quickstart

Every provider client exposes .agent(model), returning an AgentBuilder:

use rig_core::prelude::*;
use rig_core::providers::anthropic;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = anthropic::Client::from_env()?;

    let agent = client
        .agent(anthropic::completion::CLAUDE_SONNET_4_6)
        .preamble("Answer concisely.")
        .temperature(0.0)
        .build();

    let answer = agent.prompt("What is Rig?").await?;
    println!("{answer}");
    Ok(())
}

from_env() reads provider credentials from environment variables — no API key touches application code. .agent() takes impl Into<String> for the model argument: a provider module constant (anthropic::completion::CLAUDE_SONNET_4_6) or a raw string both work. See references/providers.md for the constants available per provider and the env-var contract each from_env() reads.

Hybrid multi-provider harness

A single Rust process commonly needs several models at once — a cheap model for extraction, a mid-tier model for the main loop, a strong model for review, one of them local. Rig provides the primitives (clients, AgentBuilder, the CompletionModel trait) — it does not ship a built-in multi-tier harness type. The tier-selection pattern in references/providers.md is guidance built on those primitives, not a first-party rig recipe.