# `LangChain.Utils.ChatTemplates`
[🔗](https://github.com/brainlid/langchain/blob/v0.9.3/lib/utils/chat_templates.ex#L1)

Functions for converting messages into the various commonly used chat template
formats.

## Format examples

There are currently no industry standards around model's chat formats. For any
given model, it's documentation and config may need to be inspected for it's
format, and it may be something not supported at this time.

### `:inst`

```
<s>[INST] System message. User message. [/INST]
Assistant response
[INST] User message. [/INST]</s>
Assistant response
```

Note: The `:inst` format has no concept of a system message. It will be
combined with the first user message

### `:im_start`

```
<|im_start|>user
User message.<|im_end|>
<|im_start|>assistant
Assistant response.<|im_end|>
<|im_start|>user
User message.<|im_end|>
<|im_start|>assistant
```

Note: The `:im_start` format has no concept of a system message. It will be
combined with the first user message.

### `:llama_2`

```
<s>[INST] <<SYS>>
System message.
<</SYS>>

User message [/INST] Assistant response </s><s>[INST] User message. [/INST]
```

Note: The `:llama_2` format supports specific system messages. It is a
variation of the `:inst` format.

### `:llama_3`

```
<|begin_of_text|>
<|start_header_id|>system<|end_header_id|>

System message.<|eot_id|>
<|start_header_id|>user<|end_header_id|>

User message.<|eot_id|>
<|start_header_id|>assistant<|end_header_id|>

Assistant message.<|eot_id|>
```

### `:zephyr`

```
<|system|>
System message.</s>
<|user|>
User message.</s>
<|assistant|>
Assistant message.
<|user|>
User message.</s>
```

Note: The `:zephyr` format supports specific system messages.

### `:phi_4`

The `:phi_4` template format is also supported.

## Template callback

It's possible to pass a callback as a template.
The function receives the list of messages as first argument and `opts` as second and must return a string.

# `chat_format`
[🔗](https://github.com/brainlid/langchain/blob/v0.9.3/lib/utils/chat_templates.ex#L105)

```elixir
@type chat_format() ::
  :inst
  | :im_start
  | :llama_2
  | :llama_3
  | :phi_4
  | :zephyr
  | template_callback()
```

# `template_callback`
[🔗](https://github.com/brainlid/langchain/blob/v0.9.3/lib/utils/chat_templates.ex#L104)

```elixir
@type template_callback() :: ([LangChain.Message.t()], Keyword.t() -&gt; String.t())
```

# `apply_chat_template!`
[🔗](https://github.com/brainlid/langchain/blob/v0.9.3/lib/utils/chat_templates.ex#L197)

```elixir
@spec apply_chat_template!(
  [LangChain.Message.t()],
  chat_format(),
  opts :: Keyword.t()
) ::
  String.t() | no_return()
```

Transform a list of messages into a text prompt in the desired format for the
LLM.

## Options

- `:add_generation_prompt` - Boolean. Defaults to `true` when the last message
  is a user prompt. Depending on the format, when a user message is the last
  message, then the text prompt should begin the portion for the assistant to
  trigger the assistant's text generation.

# `apply_chat_template_with_tools!`
[🔗](https://github.com/brainlid/langchain/blob/v0.9.3/lib/utils/chat_templates.ex#L390)

Transform a list of messages into a text prompt in the desired format for the
LLM.
And adds tool configuration.

## Options

- `:add_generation_prompt` - Boolean. Defaults to `true` when the last message
  is a user prompt. Depending on the format, when a user message is the last
  message, then the text prompt should begin the portion for the assistant to
  trigger the assistant's text generation.

# `llama_3_1_custom_tool_calling_parameter_conversion`
[🔗](https://github.com/brainlid/langchain/blob/v0.9.3/lib/utils/chat_templates.ex#L651)

# `prep_and_validate_messages`
[🔗](https://github.com/brainlid/langchain/blob/v0.9.3/lib/utils/chat_templates.ex#L134)

```elixir
@spec prep_and_validate_messages([LangChain.Message.t()]) ::
  {LangChain.Message.t() | nil, LangChain.Message.t(), [LangChain.Message.t()]}
  | no_return()
```

Validate that the message are in a supported format. Returns the system
message (or uses a default one).

Returns: `{System Message, First User Message, Other Messages}`

If there is an issue, an exception is raised. Reasons for an exception:

- Only 1 system message is allowed and, if included, it is the first message.
- Non-system messages must begin with a user message or assistant message.

Recent change:
- Alternating messages between user / assistant / user / assistant are no longer enforced as not every model has issues.
- It is up to the programmer to enforce this if this is something they need.

---

*Consult [api-reference.md](api-reference.md) for complete listing*