What are the best AI agent frameworks?

There's no single best AI agent framework — the right pick depends on what you're building. The ones people actually reach for today are LangGraph, CrewAI, AutoGen (now folded into Microsoft Agent Framework), the OpenAI Agents SDK, LlamaIndex, Google's Agent Development Kit (ADK), and Pydantic AI. Each is strongest at a different kind of job.

Which frameworks are worth knowing?

These are the actively used options and what each is good for:

• LangGraph — models an agent as an explicit state graph with loops, branching, retries, and human-in-the-loop checkpoints. Most control, steeper learning curve; a common choice for production workflows.
• CrewAI — spins up role-based teams of agents (a "crew") with very little code. The fastest way to prototype a multi-agent system.
• AutoGen / Microsoft Agent Framework — event-driven, conversation-style coordination between multiple agents, with tight ties to the Microsoft and Semantic Kernel stack.
• OpenAI Agents SDK — lightweight path for a single agent that calls a few tools, with built-in tracing and support for the Model Context Protocol.
• LlamaIndex — built around data. If your agent needs to search large document collections or connect to many data sources, its connectors and retrieval are the draw.
• Google ADK — built for the Gemini and Vertex AI ecosystem, with strong support for multimodal work across text, images, audio, and video.
• Pydantic AI — aimed at Python developers who want type safety, validated tool inputs, and structured, predictable outputs.

How do you pick one?

Match the framework to the shape of your work, not to a leaderboard. If the job splits into specialist roles, CrewAI is quick. If one workflow needs cycles, branching, or an approval step, LangGraph gives you that control.

Heavy document retrieval points to LlamaIndex; a Google-centric or multimodal stack points to ADK; strict typing points to Pydantic AI.

Do you even need a framework?

Not always. For a single agent that calls one or two tools, a plain SDK plus your own loop can be simpler than any framework, and easier to debug. Frameworks earn their keep once you need multiple coordinated agents, complex control flow, or the observability and memory features they bundle in.