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18db07c292
Adding `create_react_agent` and introducing `langchain.agents`!
## Enhanced Structured Output
`create_react_agent` supports coercion of outputs to structured data
types like `pydantic` models, dataclasses, typed dicts, or JSON schemas
specifications.
### Structural Changes
In langgraph < 1.0, `create_react_agent` implemented support for
structured output via an additional LLM call to the model after the
standard model / tool calling loop finished. This introduced extra
expense and was unnecessary.
This new version implements structured output support in the main loop,
allowing a model to choose between calling tools or generating
structured output (or both).
The same basic pattern for structured output generation works:
```py
from langchain.agents import create_react_agent
from langchain_core.messages import HumanMessage
from pydantic import BaseModel
class Weather(BaseModel):
temperature: float
condition: str
def weather_tool(city: str) -> str:
"""Get the weather for a city."""
return f"it's sunny and 70 degrees in {city}"
agent = create_react_agent("openai:gpt-4o-mini", tools=[weather_tool], response_format=Weather)
print(repr(result["structured_response"]))
#> Weather(temperature=70.0, condition='sunny')
```
### Advanced Configuration
The new API exposes two ways to configure how structured output is
generated. Under the hood, LangChain will attempt to pick the best
approach if not explicitly specified. That is, if provider native
support is available for a given model, that takes priority over
artificial tool calling.
1. Artificial tool calling (the default for most models)
LangChain generates a tool (or tools) under the hood that match the
schema of your response format. When the model calls those tools,
LangChain coerces the args to the desired format. Note, LangChain does
not validate outputs adhering to JSON schema specifications.
<details>
<summary>Extended example</summary>
```py
from langchain.agents import create_react_agent
from langchain_core.messages import HumanMessage
from langchain.agents.structured_output import ToolStrategy
from pydantic import BaseModel
class Weather(BaseModel):
temperature: float
condition: str
def weather_tool(city: str) -> str:
"""Get the weather for a city."""
return f"it's sunny and 70 degrees in {city}"
agent = create_react_agent(
"openai:gpt-4o-mini",
tools=[weather_tool],
response_format=ToolStrategy(
schema=Weather, tool_message_content="Final Weather result generated"
),
)
result = agent.invoke({"messages": [HumanMessage("What's the weather in Tokyo?")]})
for message in result["messages"]:
message.pretty_print()
"""
================================ Human Message =================================
What's the weather in Tokyo?
================================== Ai Message ==================================
Tool Calls:
weather_tool (call_Gg933BMHMwck50Q39dtBjXm7)
Call ID: call_Gg933BMHMwck50Q39dtBjXm7
Args:
city: Tokyo
================================= Tool Message =================================
Name: weather_tool
it's sunny and 70 degrees in Tokyo
================================== Ai Message ==================================
Tool Calls:
Weather (call_9xOkYUM7PuEXl9DQq9sWGv5l)
Call ID: call_9xOkYUM7PuEXl9DQq9sWGv5l
Args:
temperature: 70
condition: sunny
================================= Tool Message =================================
Name: Weather
Final Weather result generated
"""
print(repr(result["structured_response"]))
#> Weather(temperature=70.0, condition='sunny')
```
</details>
2. Provider implementations (limited to OpenAI, Groq)
Some providers support structured output generating directly. For those
cases, we offer the `ProviderStrategy` hint:
<details>
<summary>Extended example</summary>
```py
from langchain.agents import create_react_agent
from langchain_core.messages import HumanMessage
from langchain.agents.structured_output import ProviderStrategy
from pydantic import BaseModel
class Weather(BaseModel):
temperature: float
condition: str
def weather_tool(city: str) -> str:
"""Get the weather for a city."""
return f"it's sunny and 70 degrees in {city}"
agent = create_react_agent(
"openai:gpt-4o-mini",
tools=[weather_tool],
response_format=ProviderStrategy(Weather),
)
result = agent.invoke({"messages": [HumanMessage("What's the weather in Tokyo?")]})
for message in result["messages"]:
message.pretty_print()
"""
================================ Human Message =================================
What's the weather in Tokyo?
================================== Ai Message ==================================
Tool Calls:
weather_tool (call_OFJq1FngIXS6cvjWv5nfSFZp)
Call ID: call_OFJq1FngIXS6cvjWv5nfSFZp
Args:
city: Tokyo
================================= Tool Message =================================
Name: weather_tool
it's sunny and 70 degrees in Tokyo
================================== Ai Message ==================================
{"temperature":70,"condition":"sunny"}
Weather(temperature=70.0, condition='sunny')
"""
print(repr(result["structured_response"]))
#> Weather(temperature=70.0, condition='sunny')
```
Note! The final tool message has the custom content provided by the dev.
</details>
Prompted output was previously supported and is no longer supported via
the `response_format` argument to `create_react_agent`. If there's
significant demand for this, we'd be happy to engineer a solution.
## Error Handling
`create_react_agent` now exposes an API for managing errors associated
with structured output generation. There are two common problems with
structured output generation (w/ artificial tool calling):
1. **Parsing error** -- the model generates data that doesn't match the
desired structure for the output
2. **Multiple tool calls error** -- the model generates 2 or more tool
calls associated with structured output schemas
A developer can control the desired behavior for this via the
`handle_errors` arg to `ToolStrategy`.
<details>
<summary>Extended example</summary>
```py
from langchain_core.messages import HumanMessage
from pydantic import BaseModel
from langchain.agents import create_react_agent
from langchain.agents.structured_output import StructuredOutputValidationError, ToolStrategy
class Weather(BaseModel):
temperature: float
condition: str
def weather_tool(city: str) -> str:
"""Get the weather for a city."""
return f"it's sunny and 70 degrees in {city}"
def handle_validation_error(error: Exception) -> str:
if isinstance(error, StructuredOutputValidationError):
return (
f"Please call the {error.tool_name} call again with the correct arguments. "
f"Your mistake was: {error.source}"
)
raise error
agent = create_react_agent(
"openai:gpt-5",
tools=[weather_tool],
response_format=ToolStrategy(
schema=Weather,
handle_errors=handle_validation_error,
),
)
```
</details>
## Error Handling for Tool Calling
Tools fail for two main reasons:
1. **Invocation failure** -- the args generated by the model for the
tool are incorrect (missing, incompatible data types, etc)
2. **Execution failure** -- the tool execution itself fails due to a
developer error, network error, or some other exception.
By default, when tool **invocation** fails, the react agent will return
an artificial `ToolMessage` to the model asking it to correct its
mistakes and retry.
Now, when tool **execution** fails, the react agent raises the
`ToolException` by default instead of asking the model to retry. This
helps to avoid looping that should be avoided due to the aforementioned
issues.
Developers can configure their desired behavior for retries / error
handling via the `handle_tool_errors` arg to `ToolNode`.
## Pre-Bound Models
`create_react_agent` no longer supports inputs to `model` that have been
pre-bound w/ tools or other configuration. To properly support
structured output generation, the agent itself needs the power to bind
tools + structured output kwargs.
This also makes the devx cleaner - it's always expected that `model` is
an instance of `BaseChatModel` (or `str` that we coerce into a chat
model instance).
Dynamic model functions can return a pre-bound model **IF** structured
output is not also used. Dynamic model functions can then bind tools /
structured output logic.
## Import Changes
Users should now use `create_react_agent` from `langchain.agents`
instead of `langgraph.prebuilts`.
Other imports have a similar migration path, `ToolNode` and `AgentState`
for example.
* `chat_agent_executor.py` -> `react_agent.py`
Some notes:
1. Disabled blockbuster + some linting in `langchain/agents` -- beyond
ideal, but necessary to get this across the line for the alpha. We
should re-enable before official release.
Note
Looking for the JS/TS library? Check out LangChain.js.
LangChain is a framework for building LLM-powered applications. It helps you chain together interoperable components and third-party integrations to simplify AI application development — all while future-proofing decisions as the underlying technology evolves.
pip install -U langchain
To learn more about LangChain, check out the docs. If you’re looking for more advanced customization or agent orchestration, check out LangGraph, our framework for building controllable agent workflows.
Why use LangChain?
LangChain helps developers build applications powered by LLMs through a standard interface for models, embeddings, vector stores, and more.
Use LangChain for:
- Real-time data augmentation. Easily connect LLMs to diverse data sources and external/internal systems, drawing from LangChain’s vast library of integrations with model providers, tools, vector stores, retrievers, and more.
- Model interoperability. Swap models in and out as your engineering team experiments to find the best choice for your application’s needs. As the industry frontier evolves, adapt quickly — LangChain’s abstractions keep you moving without losing momentum.
LangChain’s ecosystem
While the LangChain framework can be used standalone, it also integrates seamlessly with any LangChain product, giving developers a full suite of tools when building LLM applications.
To improve your LLM application development, pair LangChain with:
- LangSmith - Helpful for agent evals and observability. Debug poor-performing LLM app runs, evaluate agent trajectories, gain visibility in production, and improve performance over time.
- LangGraph - Build agents that can reliably handle complex tasks with LangGraph, our low-level agent orchestration framework. LangGraph offers customizable architecture, long-term memory, and human-in-the-loop workflows — and is trusted in production by companies like LinkedIn, Uber, Klarna, and GitLab.
- LangGraph Platform - Deploy and scale agents effortlessly with a purpose-built deployment platform for long-running, stateful workflows. Discover, reuse, configure, and share agents across teams — and iterate quickly with visual prototyping in LangGraph Studio.
Additional resources
- Tutorials: Simple walkthroughs with guided examples on getting started with LangChain.
- How-to Guides: Quick, actionable code snippets for topics such as tool calling, RAG use cases, and more.
- Conceptual Guides: Explanations of key concepts behind the LangChain framework.
- LangChain Forum: Connect with the community and share all of your technical questions, ideas, and feedback.
- API Reference: Detailed reference on navigating base packages and integrations for LangChain.
- Chat LangChain: Ask questions & chat with our documentation.