Best AI tools for building ai agents in 2026

Frameworks, protocols and observability for building agents.

1. OpenAI Agents SDK (Agent framework)

   Lightweight framework for building multi-agent workflows with tools, handoffs and tracing.

   Pricing: Open source (MIT); pay for model API usage · Visit OpenAI Agents SDK

2. LangGraph (Agent framework)

   Library for building stateful, long-running agents as graphs, with persistence and human-in-the-loop.

   Pricing: Open source; paid LangGraph Platform/LangSmith · Visit LangGraph

3. CrewAI (Agent framework)

   Python framework for orchestrating role-based teams of agents.

   Pricing: Open source framework; paid enterprise platform · Visit CrewAI

4. Pydantic AI (Agent framework)

   Python agent framework built by the Pydantic team with type-safe outputs.

   Pricing: Free, open source · Visit Pydantic AI

5. Mastra (Agent framework)

   TypeScript framework for building AI agents, workflows and RAG.

   Pricing: Open source; paid cloud · Visit Mastra

6. AI SDK (Agent framework)

   TypeScript toolkit for building AI apps and agents across model providers.

   Pricing: Free, open source · Visit AI SDK

7. LlamaIndex (Agent framework)

   Framework for building agents and RAG apps over your data; LlamaCloud for parsing.

   Pricing: Open source; paid LlamaCloud · Visit LlamaIndex

8. AutoGen (Agent framework)

   Open-source framework from Microsoft for multi-agent applications.

   Pricing: Free, open source · Visit AutoGen

9. Model Context Protocol (Protocol)

   Open protocol for connecting AI apps and agents to tools and data sources through MCP servers.

   Pricing: Open standard, free · Visit Model Context Protocol

10. LangSmith (Observability)

    Tracing, evaluation and monitoring platform for LLM apps and agents.

    Pricing: Free Developer tier; paid Plus and Enterprise · Visit LangSmith