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*   [Callbacks](/v0.1/docs/modules/callbacks/)
*   How-to
*   Creating custom callback handlers

Creating custom callback handlers
=================================

You can also create your own handler by implementing the `BaseCallbackHandler` interface. This is useful if you want to do something more complex than just logging to the console, eg. send the events to a logging service. As an example here is a simple implementation of a handler that logs to the console:

tip

See [this section for general instructions on installing integration packages](/v0.1/docs/get_started/installation/#installing-integration-packages).

*   npm
*   Yarn
*   pnpm

    npm install @langchain/community

    yarn add @langchain/community

    pnpm add @langchain/community

    import { Serialized } from "@langchain/core/load/serializable";import { BaseCallbackHandler } from "@langchain/core/callbacks/base";import { AgentAction, AgentFinish } from "@langchain/core/agents";import { ChainValues } from "@langchain/core/utils/types";export class MyCallbackHandler extends BaseCallbackHandler {  name = "MyCallbackHandler";  async handleChainStart(chain: Serialized) {    console.log(`Entering new ${chain.id} chain...`);  }  async handleChainEnd(_output: ChainValues) {    console.log("Finished chain.");  }  async handleAgentAction(action: AgentAction) {    console.log(action.log);  }  async handleToolEnd(output: string) {    console.log(output);  }  async handleText(text: string) {    console.log(text);  }  async handleAgentEnd(action: AgentFinish) {    console.log(action.log);  }}

#### API Reference:

*   [Serialized](https://api.js.langchain.com/types/langchain_core_load_serializable.Serialized.html) from `@langchain/core/load/serializable`
*   [BaseCallbackHandler](https://api.js.langchain.com/classes/langchain_core_callbacks_base.BaseCallbackHandler.html) from `@langchain/core/callbacks/base`
*   [AgentAction](https://api.js.langchain.com/types/langchain_core_agents.AgentAction.html) from `@langchain/core/agents`
*   [AgentFinish](https://api.js.langchain.com/types/langchain_core_agents.AgentFinish.html) from `@langchain/core/agents`
*   [ChainValues](https://api.js.langchain.com/types/langchain_core_utils_types.ChainValues.html) from `@langchain/core/utils/types`

You could then use it as described in the [section](#built-in-handlers) above.

* * *

#### Help us out by providing feedback on this documentation page:

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