# Best AI agent tools for building agents

Canonical: https://theagenticweekly.com/best/agent-building · Last updated: 2026-10-26 · 33 tools ranked

> If you are looking for AI agent tools, our current #1 for building agents is Claude Code, with the OpenAI Agents SDK second and LangGraph third. These are editorial picks, and most were smoke-tested on 2026-10-25 without vendor models. LangGraph and FastMCP ran with no LLM at all.

Building your own agent means picking tools for tool-calling, memory, sandboxing and deployment. We track the releases that matter for that.

## Kinds of AI agent tools

- **Frameworks and SDKs** for writing agents in code: [LangGraph](https://theagenticweekly.com/tools/langgraph), [CrewAI](https://theagenticweekly.com/tools/crewai), [OpenAI Agents SDK](https://theagenticweekly.com/tools/openai-agents-sdk), [Google ADK](https://theagenticweekly.com/tools/google-adk) and [Mastra](https://theagenticweekly.com/tools/mastra).
- **Tool servers** that let agents reach other systems: [FastMCP](https://theagenticweekly.com/tools/fastmcp) builds servers for the Model Context Protocol. See [what is an MCP server](https://theagenticweekly.com/what-is/mcp-server).
- **Workflow automation:** [n8n](https://theagenticweekly.com/tools/n8n).
- **Coding agents** used as a base for agent workflows: [Claude Code](https://theagenticweekly.com/tools/claude-code).

Rankings are editorial. Paid placements never affect them. Reported = written from official sources; Tested = a small smoke test whose scope is stated per tool (not a benchmark). How ranks are chosen: https://theagenticweekly.com/editorial-policy#ranking.

## Our ranked list

| Rank | Tool | Why | Verdict | Evidence | Last verified |
|---|---|---|---|---|---|
| 1 | [Claude Code](https://theagenticweekly.com/tools/claude-code) | Plugins, skills, hooks and an Agent SDK are referenced in the changelog, which makes it a base for building your own agent workflows. | Update now if you use the sandbox or run Claude Code on a cloud provider; skip if you wanted flashy new features, this is a hardening release. | Tested (smoke test, 2026-10-25, local Qwen2.5-3B-Instruct, not vendor models) | 2026-10-25 |
| 2 | [OpenAI Agents SDK](https://theagenticweekly.com/tools/openai-agents-sdk) | MIT-licensed framework with MCP, sessions, tracing and realtime voice examples. | Pick it if you want a small, official framework for multi-agent flows on the OpenAI API; the update is incremental. | Tested (smoke test, 2026-10-25, local Qwen2.5-3B-Instruct, not vendor models) | 2026-10-25 |
| 3 | [LangGraph](https://theagenticweekly.com/tools/langgraph) | MIT-licensed graph framework for stateful agents; the latest release is a patch. | A dependable foundation for stateful agents; this release is a routine fix, so only update if the RemoteGraph or recursion fixes affect you. | Tested (smoke test, 2026-10-25, local 3B model (Qwen2.5-3B)) | 2026-10-25 |
| 4 | [Google ADK](https://theagenticweekly.com/tools/google-adk) | Apache-2.0 toolkit with evaluation, live audio and new MongoDB services. | Update with care: a big, useful release for Gemini users, but it includes a telemetry default change. | Tested (smoke test, 2026-10-25, local Qwen2.5-3B-Instruct, not vendor models) | 2026-10-25 |
| 5 | [CrewAI](https://theagenticweekly.com/tools/crewai) | MIT framework with crew-style orchestration and a new eval command. | Reasonable if you like the crew-of-agents mental model; the memory and tool-loop fixes in this release are worth taking. | Tested (smoke test, 2026-10-25, local Qwen2.5-3B-Instruct, not vendor models) | 2026-10-25 |
| 6 | [Mastra](https://theagenticweekly.com/tools/mastra) | TypeScript-first framework with Studio, observability and MCP support. | A strong TypeScript option if you are building agents in a Node stack; read the breaking-change note on sessions before upgrading. | Tested (smoke test, 2026-10-25, local 3B model (Qwen2.5-3B)) | 2026-10-25 |
| 7 | [FastMCP](https://theagenticweekly.com/tools/fastmcp) | A widely used Python library for MCP servers; the October releases are security-focused. | If you run FastMCP servers, upgrade and read the security notices; the OAuth issuer step is not automatic. | Tested (smoke test, 2026-10-25, no language model involved) | 2026-10-25 |
| 8 | [n8n](https://theagenticweekly.com/tools/n8n) | Visual workflows plus native AI agents, with an agent builder and budget tracking. | Great fit for small teams that want to wire apps and AI together without code; the license is fair-code, not open source. | Tested (smoke test, 2026-10-25, local 3B model (Qwen2.5-3B)) | 2026-10-25 |
| 9 | [Langflow](https://theagenticweekly.com/tools/langflow) | Low-code visual builder for agents, RAG and MCP servers. | MIT-licensed visual builder for AI agents and MCP servers with a very large GitHub following. | Tested (smoke test, 2026-10-26, no LLM involved) | 2026-10-26 |
| 10 | [Botpress](https://theagenticweekly.com/tools/botpress) | Agent platform for customer support with per-conversation pricing. | Customer-support AI agent platform with a free plan and conversation-based paid plans. | Reported (not run by us) | 2026-10-25 |
| 11 | [Gumloop](https://theagenticweekly.com/tools/gumloop) | Multiplayer agent builder with credit pricing. | Agent builder for teams; plans start at $37 per month with 20k included credits. | Reported (not run by us) | 2026-10-25 |
| 12 | [Lindy](https://theagenticweekly.com/tools/lindy) | No-code AI employee builder with credit-based plans. | AI 'employee' builder that connects to your tools; Free plan with $50 in credits that last 7 days, then credit-based plans. | Reported (not run by us) | 2026-10-25 |
| 13 | [Microsoft Copilot Studio](https://theagenticweekly.com/tools/copilot-studio) | Microsoft's low-code platform for custom agents. | Microsoft's platform for creating and managing custom agents, workflows and apps with no code. | Reported (not run by us) | 2026-10-25 |
| 14 | [Pydantic AI](https://theagenticweekly.com/tools/pydantic-ai) | Type-safe Python agent framework from the Pydantic team. | Python agent framework built on Pydantic types, covering agents, realtime voice, image generation and embeddings. | Tested (smoke test, 2026-10-25, local 3B model (Qwen2.5-3B)) | 2026-10-25 |
| 15 | [Relevance AI](https://theagenticweekly.com/tools/relevance-ai) | Specialist agents for sales, support and marketing. | Platform for specialist AI agents for sales, customer success, marketing and HR, with an embedded deployment team. | Reported (not run by us) | 2026-10-25 |
| 16 | [Voiceflow](https://theagenticweekly.com/tools/voiceflow) | Enterprise chat and voice agent platform. | Platform for chat and voice AI agents for customer experience teams. | Reported (not run by us) | 2026-10-25 |
| 17 | [Vercel AI SDK](https://theagenticweekly.com/tools/vercel-ai-sdk) | TypeScript toolkit for LLM apps, streaming UIs and agents. | Vercel's TypeScript SDK that gives one API across many model providers, with streaming and agent helpers. | Tested (smoke test, 2026-10-25, local 3B model (Qwen2.5-3B)) | 2026-10-25 |
| 18 | [Agno](https://theagenticweekly.com/tools/agno) | Python agent framework and self-hosted agent platform. | Open-source agent framework that now sells a self-driving agent platform you run in your own cloud. | Tested (smoke test, 2026-10-25, local 3B model (Qwen2.5-3B)) | 2026-10-25 |
| 19 | [Composio](https://theagenticweekly.com/tools/composio) | Tool and auth layer connecting agents to 1,500+ apps. | Managed tool-calling and authentication for agents across 1,500+ apps, with a free tier of 100,000 tool calls a month. | Reported (not run by us) | 2026-10-25 |
| 20 | [Dify](https://theagenticweekly.com/tools/dify) | Visual LLM app and agent builder, self-hostable under a modified Apache license. | Open-source platform for building LLM apps and agent workflows with a visual canvas; licensed under a modified Apache 2.0 with extra conditions. | Reported (not run by us) | 2026-10-25 |
| 21 | [OpenHands](https://theagenticweekly.com/tools/openhands) | Automations and SDK for building engineering agents. | Open-source AI coding agent platform you can start locally, automate with workflows and run with any model. | Reported (not run by us) | 2026-10-25 |
| 22 | [LangChain](https://theagenticweekly.com/tools/langchain) | The most-starred Python and JS framework for LLM apps and agents. | Open-source framework for building LLM applications and agents in Python and JavaScript, from the team behind LangGraph and LangSmith. | Tested (smoke test, 2026-10-25, local 3B model (Qwen2.5-3B)) | 2026-10-25 |
| 23 | [Haystack](https://theagenticweekly.com/tools/haystack) | Open-source Python framework for RAG and agent pipelines. | Apache-2.0 Python framework for building search, RAG and agent pipelines, maintained by deepset. | Tested (smoke test, 2026-10-25, local 3B model (Qwen2.5-3B)) | 2026-10-25 |
| 24 | [Browser Use](https://theagenticweekly.com/tools/browser-use) | Open-source library and cloud browsers for web agents. | Open-source library that lets AI agents drive a browser, with a pay-as-you-go cloud browser starting at $0.02 an hour. | Reported (not run by us) | 2026-10-25 |
| 25 | [DSPy](https://theagenticweekly.com/tools/dspy) | MIT-licensed Python framework for composing and optimising LM programs. | Worth a look if you want structured, testable LM pipelines; start with a plain Predict module before optimisers. | Tested (smoke test, 2026-10-25, local 3B model (Qwen2.5-3B)) | 2026-10-25 |
| 26 | [Semantic Kernel](https://theagenticweekly.com/tools/semantic-kernel) | Microsoft SDK for AI agents in .NET, Python and Java; successor is Microsoft Agent Framework. | Microsoft's model-agnostic SDK for building AI agents; its README calls Microsoft Agent Framework the enterprise-ready successor. | Reported (not run by us) | 2026-10-25 |
| 27 | [Mem0](https://theagenticweekly.com/tools/mem0) | Memory layer API for agents and apps. | Open-source and hosted memory layer that lets agents remember users across sessions, with a free tier and published request quotas. | Tested (smoke test, 2026-10-26, local 3B model plus a local embedder) | 2026-10-26 |
| 28 | [LlamaIndex](https://theagenticweekly.com/tools/llamaindex) | Data framework for RAG and document agents. | Open-source data framework for retrieval-augmented generation and document-centred agents, with a hosted document platform alongside. | Tested (smoke test, 2026-10-25, local 3B model (Qwen2.5-3B)) | 2026-10-25 |
| 29 | [Instructor](https://theagenticweekly.com/tools/instructor) | MIT-licensed structured-output library built on Pydantic. | A small, light way to get typed output from a model; good first step before reaching for a full framework. | Tested (smoke test, 2026-10-25, local 3B model (Qwen2.5-3B)) | 2026-10-25 |
| 30 | [Flowise](https://theagenticweekly.com/tools/flowise) | Open-source visual LLM-flow builder; GitHub repository is archived. | Open-source drag-and-drop builder for LLM flows and agents; GitHub marks the main repository as archived with its last push in Aug 2026. | Reported (not run by us) | 2026-10-25 |
| 31 | [smolagents](https://theagenticweekly.com/tools/smolagents) | Minimal Hugging Face library for code-writing agents. | Hugging Face's small Python library for agents that write and run code; the docs say the core logic fits in roughly a thousand lines. | Tested (smoke test, 2026-10-25, local 3B model (Qwen2.5-3B)) | 2026-10-25 |
| 32 | [Letta](https://theagenticweekly.com/tools/letta) | Stateful agents with persistent memory. | Platform and open-source framework for stateful agents that keep and improve memory across sessions. | Reported (not run by us) | 2026-10-25 |
| 33 | [AutoGen](https://theagenticweekly.com/tools/autogen) | Microsoft's multi-agent framework, now steering users to Microsoft Agent Framework. | Microsoft's open-source multi-agent framework; its README now says the project is in maintenance mode and points to Microsoft Agent Framework. | Tested (smoke test, 2026-10-25, local 3B model (Qwen2.5-3B)) | 2026-10-25 |

## Comparisons

For a head-to-head read of two frameworks, see [LangGraph vs CrewAI](https://theagenticweekly.com/compare/langgraph-vs-crewai). We have not run them against each other.

## FAQ

### What are the best AI agent tools?

For building your own agents we rank Claude Code first, then the OpenAI Agents SDK and LangGraph. The ranking is editorial, and the ranked list on this page shows each tool's evidence label.

### Which agent frameworks are open source?

LangGraph and CrewAI are MIT-licensed. See each tool page for its licence as read from its repository.

## How to cite

Agentic Weekly, "Best AI tools for building agents (updated weekly)", last updated 2026-10-26, https://theagenticweekly.com/best/agent-building