LangChain Reference home page

GitHub
Main Docs

Overview
Caches
Callbacks
Documents
Document loaders
Embeddings
Exceptions
Language models
Serialization
Output parsers
Prompts
Rate limiters
Retrievers
Runnables
Utilities
Vector stores

MCP Adapters

Standard Tests

Text Splitters

⌘I

LangChain Assistant

Ask a question to get started

Enter to send•Shift+Enter new line

Menu

Overview Caches Callbacks Documents Document loaders Embeddings Exceptions Language models Serialization Output parsers Prompts Rate limiters Retrievers Runnables Utilities Vector stores

Language

Theme

Pythonlangchain-corecallbacksstdoutStdOutCallbackHandleron_chain_start

Method●Since v0.1

on_chain_start

Copy

on_chain_start(
  self,
  serialized: dict[str, Any],
  inputs: dict[str

View source on GitHub

,

Any

]

,

**

kwargs

:

=

{

}

)

->

None

Parameters

Name	Type	Description
`serialized`*	`dict[str, Any]`	The serialized chain.
`inputs`*	`dict[str, Any]`	The inputs to the chain.
`**kwargs`	`Any`	Default:`{}`

Print out that we are entering a chain.

Additional keyword arguments.