Best AI agent frameworks for builders (2026)

⚡ Quick verdict

LangGraph is our top pick for complex, stateful agents. Vercel AI SDK is the pick for AI features and agents inside a TypeScript web app, and Mastra for TypeScript agent backends. All five frameworks are free to start; you mostly pay your model provider.

📊 Comparison

Tool	Starting price	Free tier	Best for	Strengths	Weaknesses
LangGraph	$39/seat/mo (LangSmith Plus) checked 2026-10-15 · source	Yes	Complex stateful agents	Durable execution, memory and human-in-the-loop for stateful agents Open-source framework	Paid observability comes from LangSmith ($39/seat/mo Plus)
Vercel AI SDK	Free (pay your model provider) checked 2026-10-15 · source	Yes	AI features in web apps	TypeScript toolkit for AI features and agents in web apps Free and open source; you pay only your model provider
Mastra	$250/mo (Teams, hosted) checked 2026-10-15 · source	Yes	TS agent backends	TypeScript framework for agent backends Open source; hosted Starter plan is $0/mo with usage-based overages	Hosted Teams plan is $250/mo
OpenAI Agents SDK	Free (pay model usage) checked 2026-10-15 · source	Yes	OpenAI-based agents	Lightweight SDK for multi-agent workflows Free and open source; you pay model usage
CrewAI	Enterprise: custom checked 2026-10-15 · source	Yes	Multi-agent Python	Open-source Python framework for multi-agent crews Free hosted Basic plan	Hosted Basic is capped at 50 workflow executions/month; Enterprise is custom-priced

Prices are starting paid prices from each tool's official pricing page on the date shown. Pricing changes often; check the source before you buy.

🧭 Which should you pick?

Complex stateful agents with memory and human approval: LangGraph.
AI features in a Next.js or TypeScript web app: Vercel AI SDK.
A TypeScript agent backend: Mastra.
Python agents on OpenAI models: OpenAI Agents SDK.
Multi-agent crews in Python: CrewAI.

❓ FAQ

What is the best AI agent framework?

ToolStack ranks LangGraph #1, Vercel AI SDK #2 and Mastra #3 in Agent Frameworks.

Are AI agent frameworks free?

The frameworks themselves are open source and free. Paid tiers are for hosting or observability: LangSmith Plus is $39/seat/mo, Mastra hosted Teams is $250/mo, and CrewAI has a free hosted Basic plan (50 workflow executions/month). Prices from official pages.

What else do I need to launch an agent product?

Our "Launch an AI agent product" starter stack pairs Vercel AI SDK with Claude Code, Neon, Railway and n8n.

🧱 Starter stacks

Ship an app this weekend · The indie dev stack · Launch an AI agent product

📚 More guides

Lovable vs Bolt.new · Cursor vs Claude Code · Supabase vs Firebase · Vercel vs Netlify · Best AI app builders · Best AI coding agents · Best backend for vibe coders · Best app hosting for vibe coders · Best AI voice and text-to-speech · Railway vs Render · ElevenLabs vs Cartesia · Railway vs Fly.io · Lovable vs v0 · Best payments for AI apps · Cursor alternatives

← Browse all 69 tools on ToolStack · How we rank

Best AI agent frameworks