> ## Documentation Index
> Fetch the complete documentation index at: https://docs.galileo.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# handler

## GalileoCallback

Langchain callback handler for logging traces to the Galileo platform.

**Arguments**

* `_handler` (`GalileoBaseHandler`): The handler for managing the trace.

### on\_agent\_finish

```python theme={null}
def on_agent_finish(self, finish: AgentFinish, *, run_id: UUID, **kwargs: Any) -> Any
```

Langchain callback when an agent finishes.

### on\_chain\_end

```python theme={null}
def on_chain_end(self,
                 outputs: dict[str, Any],
                 *,
                 run_id: UUID,
                 parent_run_id: Optional[UUID]=None,
                 **kwargs: Any) -> Any
```

Langchain callback when a chain ends.

### on\_chain\_error

```python theme={null}
def on_chain_error(self,
                   error: Exception,
                   *,
                   run_id: UUID,
                   parent_run_id: Optional[UUID]=None,
                   **kwargs: Any) -> Any
```

Langchain callback when a chain errors.

### on\_chain\_start

```python theme={null}
def on_chain_start(self,
                   serialized: dict[str, Any],
                   inputs: dict[str, Any],
                   *,
                   run_id: UUID,
                   parent_run_id: Optional[UUID]=None,
                   tags: Optional[list[str]]=None,
                   **kwargs: Any) -> Any
```

Langchain callback when a chain starts.

### on\_chat\_model\_start

```python theme={null}
def on_chat_model_start(self,
                        serialized: dict[str, Any],
                        messages: list[list[BaseMessage]],
                        *,
                        run_id: UUID,
                        parent_run_id: Optional[UUID]=None,
                        tags: Optional[list[str]]=None,
                        metadata: Optional[dict[str, Any]]=None,
                        **kwargs: Any) -> Any
```

Langchain callback when a chat model starts.

### on\_llm\_end

```python theme={null}
def on_llm_end(self,
               response: LLMResult,
               *,
               run_id: UUID,
               parent_run_id: Optional[UUID]=None,
               **kwargs: Any) -> Any
```

Langchain callback when an LLM node ends.

### on\_llm\_error

```python theme={null}
def on_llm_error(self,
                 error: Exception,
                 *,
                 run_id: UUID,
                 parent_run_id: Optional[UUID]=None,
                 **kwargs: Any) -> Any
```

Langchain callback when an LLM errors.

### on\_llm\_new\_token

```python theme={null}
def on_llm_new_token(self, token: str, *, run_id: UUID, **kwargs: Any) -> Any
```

Langchain callback when an LLM node generates a new token.

### on\_llm\_start

```python theme={null}
def on_llm_start(self,
                 serialized: dict[str, Any],
                 prompts: list[str],
                 *,
                 run_id: UUID,
                 parent_run_id: Optional[UUID]=None,
                 tags: Optional[list[str]]=None,
                 metadata: Optional[dict[str, Any]]=None,
                 **kwargs: Any) -> Any
```

Langchain callback when an LLM node starts.

Note: This callback is only used for non-chat models.

### on\_retriever\_end

```python theme={null}
def on_retriever_end(self,
                     documents: list[Document],
                     *,
                     run_id: UUID,
                     parent_run_id: Optional[UUID]=None,
                     **kwargs: Any) -> Any
```

Langchain callback when a retriever node ends.

### on\_retriever\_error

```python theme={null}
def on_retriever_error(self,
                       error: Exception,
                       *,
                       run_id: UUID,
                       parent_run_id: Optional[UUID]=None,
                       **kwargs: Any) -> Any
```

Langchain callback when a retriever errors.

### on\_retriever\_start

```python theme={null}
def on_retriever_start(self,
                       serialized: dict[str, Any],
                       query: str,
                       *,
                       run_id: UUID,
                       parent_run_id: Optional[UUID]=None,
                       tags: Optional[list[str]]=None,
                       metadata: Optional[dict[str, Any]]=None,
                       **kwargs: Any) -> Any
```

Langchain callback when a retriever node starts.

### on\_tool\_end

```python theme={null}
def on_tool_end(self,
                output: Any,
                *,
                run_id: UUID,
                parent_run_id: Optional[UUID]=None,
                **kwargs: Any) -> Any
```

Langchain callback when a tool node ends.

### on\_tool\_error

```python theme={null}
def on_tool_error(self,
                  error: Exception,
                  *,
                  run_id: UUID,
                  parent_run_id: Optional[UUID]=None,
                  **kwargs: Any) -> Any
```

Langchain callback when a tool errors.

### on\_tool\_start

```python theme={null}
def on_tool_start(self,
                  serialized: dict[str, Any],
                  input_str: str,
                  *,
                  run_id: UUID,
                  parent_run_id: Optional[UUID]=None,
                  tags: Optional[list[str]]=None,
                  metadata: Optional[dict[str, Any]]=None,
                  **kwargs: Any) -> Any
```

Langchain callback when a tool node starts.