LangChain

LangChain is an open-source Python and TypeScript framework for building LLM agents with a standard interface to hundreds of model and tool integrations. It supports tool calling, MCP servers, memory, structured output and tracing via LangSmith.

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LangChain at a glance

From official pages, checked Sep 29, 2026. Tap the arrow for each source.

Free tier: Free & open source
MIT library; LangSmith Developer plan is free with up to 5k base traces/month, 1 seat.
Starting price: Free, open source
Hosted LangSmith Plus is $39/seat/month with up to 10k base traces/month, then pay-as-you-go.
Rate limit: 5k traces/month
LangSmith free Developer plan, then pay-as-you-go.
Storage: Traces kept 14 days
LangSmith base traces; extended traces kept 400 days at extra cost.
Official SDKs: PythonJavaScript / TypeScript
Open source: Yes
MIT licence
Trains on your data: No
Runs in your own code; LangSmith states it does not use your data to train models.
EU hosting: Yes
LangSmith cloud offers an EU region (eu.smith.langchain.com, GCP EU).
Compliance: SOC 2ISO 27001GDPRHIPAA

What you can build with LangChain

LangChainSnippetPaste

Build a tool-calling Python agent with LangChain create_agent

Give an LLM your own Python function as a tool and let a LangChain agent decide when to call it.

Free tier: Free & open sourceFree, open source

AgentsTool calling

LangChain at a glance

What you can build with LangChain

Build a tool-calling Python agent with LangChain create_agent

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