The best open-source AI agent frameworks in 2026
The best open-source AI agent frameworks right now are LangGraph, Browser Use and Pydantic AI, out of 14 we have reviewed. Each is ranked by our rating, with its price, our verdict and who it suits.
Updated Oct 23, 2026 · Ranked from our reviews · How we review
- 1
Explicit control over every step an agent takes, paid for in code and learning time, and worth it once an agent must survive restarts and wait for a human.
Best for: Engineering teams building long-running or multi-step agents that must be reliable and auditable.
Price: Free and open source under the MIT licence. LangSmith (tracing and deployment) is separate: Developer free for one seat, Plus $39/seat/month plus compute, Enterprise custom.
Read our LangGraph review4.6/5 - 2
Browser Use is a sound base for agents that must work websites with no API, so long as someone switches off the telemetry before it sees a customer's data.
Best for: Engineering teams building agents that must operate websites without an API.
Price: Library free under MIT. Cloud is pay-as-you-go: browsers $0.02 per hour, residential proxy $5/GB, BU2 model $0.60/$3.50 per million input/output tokens, hosted agents at model price plus 20%.
Read our Browser Use review4.5/5 - 3
Pydantic AI brings the discipline of typed Python to agents, at the cost of a release train you have to pin.
Best for: Python engineers building production agents who want strong typing, testability and freedom to switch models.
Price: Free and open source under the MIT licence. Logfire observability: Personal free up to 10M records/month, Team $49/month plus $2 per extra million records. Pydantic AI Gateway adds a 5% markup on built-in providers.
Read our Pydantic AI review4.5/5 - 4
TypeScript's most complete agent toolkit, released at a pace that rewards teams who pin versions and read changelogs.
Best for: TypeScript and Next.js teams building agents and AI workflows.
Price: Core is free under Apache 2.0; code in ee/ folders needs a Mastra Enterprise licence in production. Mastra's hosted platform: Starter $0, Teams $250/month, Enterprise custom; self-hosted Enterprise is a flat annual fee.
Read our Mastra review4.4/5 - 5
The spec-first way to build MCP in Python; version 2 is cleaner, and it breaks every v1 import on the way.
Best for: Python developers building MCP servers or clients who want the official, spec-tracking implementation.
Price: Free and open source under the MIT licence.
Read our MCP Python SDK review4.4/5 - 6
A small, readable agent SDK whose defaults quietly assume OpenAI: tracing ships your runs to its dashboard, and the local sandbox trusts your machine.
Best for: Developers building agents mainly on OpenAI models who want a minimal, well-documented SDK.
Price: Free and open source under the MIT license. You pay for model usage.
Read our OpenAI Agents SDK review4.4/5 - 7
Stagehand suits engineers who want to decide, line by line, how much of a browser script a model controls, and it quietly rewards running that script on Browserbase.
Best for: Engineering teams that want AI help on the brittle parts of browser automation while keeping the rest as ordinary, testable code.
Price: SDK free under MIT. Browserbase browsers: Free 1 hour; Developer $20/month (100 hours, then $0.12/hour); Startup $99/month (500 hours, then $0.10/hour); Scale custom. Model Gateway billed at provider prices.
Read our Stagehand review4.3/5 - 8
A serious, fast-moving agent framework whose shortest road always leads to Gemini and Google Cloud, which is either the point or the catch.
Best for: Teams building agents on Gemini or deploying to Google Cloud.
Price: Free and open source under the Apache 2.0 licence. You pay for the models and Google Cloud services you use.
Read our Google Agent Development Kit (ADK) review4.2/5 - 9
Still the widest integration library for LLM apps, much tidier since 1.0, and no longer the automatic default it once was.
Best for: Teams building agents that need many provider and data integrations and may grow into custom LangGraph workflows.
Price: Free and open source under the MIT licence. LangSmith is separate: Developer free for one seat, Plus $39/seat/month, Enterprise custom.
Read our LangChain review4.2/5 - 10
The obvious home for .NET and Azure teams building agents, and a capable but less proven choice for Python teams elsewhere.
Best for: .NET and Azure teams, and anyone migrating from AutoGen or Semantic Kernel.
Price: Free and open source under the MIT licence. You pay only for the models and Azure services you use.
Read our Microsoft Agent Framework review4.2/5 - 11
Agno turns a Python agent into a served API with very little glue, but that API ships with authentication switched off.
Best for: Python teams that want to run production agents on their own infrastructure with minimal plumbing.
Price: Framework and AgentOS free under Apache 2.0. Control plane: free against a local AgentOS; Pro $150/month (one live connection, three seats, extra seats $30, SAML SSO $300); Enterprise custom.
Read our Agno review4.1/5 - 12
Fast to a working multi-agent demo and harder to steer the further it travels from one, so production teams end up writing Flows rather than Crews.
Best for: Python developers who want a multi-agent workflow running quickly and can accept less low-level control.
Price: Free and open source under the MIT licence. CrewAI AMP: Basic free with 50 workflow executions a month; Enterprise (more executions, SSO, RBAC, VPC or on-prem deployment) by quote.
Read our CrewAI review4.1/5 - 13
A sound idea, that agents work better through a command line than through screenshots, delivered as a catalogue whose quality depends on who wrote each harness.
Best for: People who want an AI agent to operate desktop applications such as Blender, GIMP or LibreOffice from the command line.
Price: Free and open source under Apache 2.0. The wrapped applications and the agent you run it in are separate.
Read our CLI-Anything review3.8/5 - 14
A clear demonstration that agents can act in code, now drifting into maintenance mode with 590 pull requests waiting.
Best for: Researchers and learners exploring code-writing agents, especially with open models.
Price: Free and open source under the Apache 2.0 license.
Read our smolagents review3.5/5