harness-sdk

Strands Agents is an open-source SDK for building and running AI agents in Python and TypeScript. Choose Strands when you would otherwise write your own agent loop: it runs in your process with no hosted control plane, and it covers the jobs a hand-rolled loop grows into. In one SDK you get lifecycle controls (turn limits, token budgets, cancellation, stop reasons), tools and structured output, MCP, multi-agent patterns, memory and sessions, model portability, streaming, guardrails, tracing, and evals.

Using a coding agent? Install the Strands plugin for Claude Code, Codex, or Cursor. It adds framework selection, scaffolding, tool authoring, MCP server connections, web framework guides, and LangGraph migration guidance. See Use Strands with AI coding agents for install and verification steps.

This monorepo contains Strands harness, the Python and TypeScript SDKs, the documentation site, and supporting packages:

Directory	Description
harness-py/	Python Strands harness: fully assembled agent via create_harness() (PyPI · docs)
harness-ts/	TypeScript Strands harness: fully assembled agent via createHarness() (npm · docs)
strands-cli/	strands CLI: prototype and chat with a harness agent from the terminal (npm)
strands-py/	Python SDK: agent loop, model providers, tools (PyPI · releases)
strands-ts/	TypeScript SDK: agent loop, model providers, tools (npm · releases)
strands-mcp/	MCP server that gives coding agents knowledge about building with Strands Agents (PyPI)

Why Strands

Build an agent harness. Control it end-to-end.

• Build your way. Any model, any cloud. Context management, execution limits, and observability built in before you write a line of config. Swap backends when you scale; your code stays the same.
• Model agnostic. First-class support for Amazon Bedrock, Anthropic, OpenAI, and Gemini, plus many more providers and custom ones.
• Stay in control. The agent loop traces every decision by default. Hooks let you intercept any step to log it, validate it, or redirect it.
• Deliver outcomes that work. Guardrails catch mistakes before they run. Steering handlers let agents correct themselves instead of failing silently.

MCP, streaming, multi-agent patterns, and structured output are all built in.

Quick Start

The easiest way to get started is with Strands harness, a fully assembled, state-of-the-art agent. A single create_harness() (Python) or createHarness() (TypeScript) call gives you an optimized agent with benchmarked defaults for the model, tools, memory, sessions, and context management — ready to take from idea to production. Follow the harness quickstart, or see the Python Strands harness and TypeScript Strands harness packages to get started.

Python

pip install strands-harness

from strands_harness import create_harness

agent = create_harness()
agent("Find the slowest test in this repo and explain why it's slow")

TypeScript

npm install @strands-agents/harness

import { createHarness } from '@strands-agents/harness'

const agent = await createHarness()
await agent.invoke("Find the slowest test in this repo and explain why it's slow")

Start here to get a batteries-included agent, then drop down to the SDKs below when you want to own the agent loop and wire up tools, model providers, and memory yourself. The harness configuration reference documents every default you can override.

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