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

# mellea.formatters.chat_formatter

> `ChatFormatter` for converting context histories to chat-message lists.

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`ChatFormatter` for converting context histories to chat-message lists.

`ChatFormatter` is the standard formatter used by mellea's legacy backends. Its
`to_chat_messages` method linearises a sequence of [`Component`](../core/base#class-component) and [`CBlock`](../core/base#class-cblock)
objects into `Message` objects with `user`, `assistant`, or `tool` roles,
handling [`ModelOutputThunk`](../core/base#class-modeloutputthunk) responses, image attachments, and parsed structured
outputs. Concrete backends call this formatter when preparing input for a chat
completion endpoint.

## Classes

<div className="w-full h-px bg-gray-200 dark:bg-gray-700 my-4" />

### <span className="ml-2 inline-flex items-center rounded-full px-2 py-1 text-[0.7rem] font-bold tracking-wide bg-[#4ADE8033]/20 text-[#15803D]">CLASS</span> `ChatFormatter` <sup><a href="https://github.com/generative-computing/mellea/blob/v0.6.0/mellea/formatters/chat_formatter.py#L21" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

Formatter used by Legacy backends to format Contexts as Messages.

<div className="h-8" />

**Methods:**

<div className="w-full h-px bg-gray-200 dark:bg-gray-700 my-4" />

#### <span className="ml-2 inline-flex items-center rounded-full px-2 py-1 text-[0.7rem] font-bold tracking-wide bg-[#3064E3]/20 text-[#1D4ED8]">FUNC</span> `to_chat_messages` <sup><a href="https://github.com/generative-computing/mellea/blob/v0.6.0/mellea/formatters/chat_formatter.py#L24" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python theme={null}
to_chat_messages(self, cs: list[Component | CBlock]) -> list[Message]
```

Convert a linearized chat history into a list of chat messages.

Iterates over each element in the context history and converts it to a
`Message` with an appropriate role. [`ModelOutputThunk`](../core/base#class-modeloutputthunk) instances are
treated as assistant responses, while all other [`Component`](../core/base#class-component) and
[`CBlock`](../core/base#class-cblock) objects default to the `user` role. Image attachments and
parsed structured outputs are handled transparently.

**Args:**

* `cs`: The linearized sequence of context
  components and code blocks to convert.

**Returns:**

* list\[Message]: A list of `Message` objects ready for submission to
  a chat completion endpoint.

<div className="w-full h-px bg-gray-200 dark:bg-gray-700 my-4" />