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Reactive Agents

Quickstart

Prerequisites

Section titled “Prerequisites”

The fastest path through this guide is the rax workflow (Rax = Reactive Agents Executable).

1. Create a Project

Section titled “1. Create a Project”

Using the CLI:

Terminal window
bunx rax init my-agent-app --template standard
cd my-agent-app
bun install

Or manually:

Terminal window
mkdir my-agent-app && cd my-agent-app
bun init -y
bun add reactive-agents

2. Set Up Environment

Section titled “2. Set Up Environment”
Terminal window
echo 'ANTHROPIC_API_KEY=sk-ant-...' > .env
echo 'GOOGLE_API_KEY=...' >> .env
echo 'TAVILY_API_KEY=tvly-...' >> .env
echo 'LITELLM_API_KEY=...' >> .env
echo 'OPENAI_API_KEY=...' >> .env

3. Build an Agent

Section titled “3. Build an Agent”

Create src/agent.ts:

import { ReactiveAgents } from "reactive-agents";


const agent = await ReactiveAgents.create()
  .withProvider("anthropic")
  .build();


const result = await agent.run("What are the three laws of thermodynamics?");
console.log(result.output);

That’s the minimum. .withProvider() picks the default model for the provider automatically (claude-sonnet-4-20250514 for Anthropic). Set ANTHROPIC_API_KEY in your environment before running.

To pin a specific model or add a name:

const agent = await ReactiveAgents.create()
  .withName("my-first-agent")
  .withProvider("anthropic")
  .withModel("claude-sonnet-4-20250514")
  .build();


const result = await agent.run("What are the three laws of thermodynamics?");
console.log("Output:", result.output);
console.log("Duration:", result.metadata.duration, "ms");
console.log("Steps:", result.metadata.stepsCount);

4. Run It

Section titled “4. Run It”
Terminal window
bun run src/agent.ts

5. Add Capabilities

Section titled “5. Add Capabilities”

Enable memory, reasoning, and safety:

const agent = await ReactiveAgents.create()
  .withName("research-agent")
  .withProvider("anthropic")
  .withModel("claude-sonnet-4-20250514")
  .withMemory() // Default memory tier (see [Memory](../memory/); use `{ tier: "enhanced" }` for embeddings)
  .withReasoning() // ReAct reasoning loop
  .withGuardrails() // Input safety checks
  .withCostTracking() // Budget enforcement
  .build();

What’s Next?

Section titled “What’s Next?”