Claude Agent SDK
A library that puts Claude Code's agent loop inside your own Python or TypeScript app. It already knows how to read files, edit them, run commands, and search the web.
Tag
harnesses
Google ADK
Google's open-source Agent Development Kit. You write an agent in code, give it tools, and can grow it into a multi-agent workflow. It is available in Python, TypeScript, Go, Java, and Kotlin.
Microsoft Agent Framework
Microsoft's open-source framework for building agents and multi-agent workflows in Python and .NET, with a Go SDK in public preview. It includes a ready-made harness for long tasks and graph workflows when you want fixed steps.
OpenAI Agents SDK
An open-source toolkit for building agents in Python and TypeScript. It runs the loop that calls a model, uses tools, hands work to another agent, and stops when the task is done.
Pydantic AI
A Python framework for typed agents. You name a model, add tools, and get answers checked against a schema. A separate harness package adds files, a shell, and planning for longer jobs.
smolagents
A small open-source Python library from Hugging Face for building agents. Its code agent writes Python to call tools and do math, instead of only returning text.