# Best Agent frameworks — The Agents Index

> Source: https://theagentsindex.com/category/frameworks (curated, quality-gated, re-verified)

Free, open-source SDKs for building your own agents — multi-agent orchestration, document retrieval, low-level control, typed output, and JS-native stacks.

16 quality-gated agents in this category. Each name links to its answer-first markdown twin.

| Name | What it is | Pricing | API |
| --- | --- | --- | --- |
| [Langflow](https://theagentsindex.com/langflow.md) | Open-source visual builder for AI agents, RAG apps and MCP servers, with an API server included. | free | Yes |
| [LangGraph](https://theagentsindex.com/langgraph.md) | Open-source orchestration framework and runtime for stateful, long-running LLM agents, from LangChain. | freemium | Yes |
| [AgentsKit](https://theagentsindex.com/agentskit.md) | Composable MIT-licensed TypeScript packages for agent runtime, tools, memory, RAG and chat UI. | free | Yes |
| [Agno](https://theagentsindex.com/agno.md) | Python SDK, open-source AgentOS runtime and hosted control plane for building and operating agents. | freemium | Yes |
| [Claude Agent SDK](https://theagentsindex.com/claude-agent-sdk.md) | Python and TypeScript library that runs Claude Code's agent loop and tools inside your own application. | paid | Yes |
| [Google Agent Development Kit (ADK)](https://theagentsindex.com/google-adk.md) | Open-source framework for building, evaluating and deploying AI agents in Python, TypeScript, Go, Java or Kotlin. | freemium | Yes |
| [Microsoft Agent Framework](https://theagentsindex.com/microsoft-agent-framework.md) | Open-source .NET, Python and Go SDK for building AI agents and graph-based multi-agent workflows. | freemium | Yes |
| [Mastra](https://theagentsindex.com/mastra.md) | Open-source TypeScript framework for building AI agents, with a hosted platform for running and observing them. | freemium | Yes |
| [Letta](https://theagentsindex.com/letta.md) | Stateful agent harness, cloud and SDK for agents with persistent, git-versioned memory. | freemium | Yes |
| [LiveKit Agents](https://theagentsindex.com/livekit-agents.md) | Open-source Python and Node.js framework for voice AI agents, with LiveKit Cloud hosting, telephony and observability. | freemium | Yes |
| [AutoGen](https://theagentsindex.com/microsoft-autogen.md) | Open-source Microsoft framework for building single and multi-agent AI applications in Python. | free | Yes |
| [LlamaIndex](https://theagentsindex.com/llamaindex.md) | Open-source agent framework plus a credit-metered document parsing, extraction and indexing platform. | freemium | Yes |
| [OpenAI Agents SDK (Python)](https://theagentsindex.com/openai-agents-sdk.md) | Open-source Python framework for building agents with tools, handoffs, guardrails and tracing. | free | Yes |
| [Pydantic AI](https://theagentsindex.com/pydantic-ai.md) | Open-source Python agent framework from the Pydantic team, with a typed agent loop and swappable models. | free | Yes |
| [CrewAI](https://theagentsindex.com/crewai.md) | Open-source multi-agent framework with a managed platform for deploying and governing agent workflows. | freemium | Yes |
| [LangChain](https://theagentsindex.com/langchain.md) | Open source agent frameworks plus LangSmith, a hosted platform to trace, evaluate, deploy and govern agents. | freemium | Yes |