docs: Add tool calling usage guide (#2866)

Signed-off-by: ayushag <ayushag@nvidia.com>
Co-authored-by: Ryan McCormick <rmccormick@nvidia.com>

docs/guides/tool_calling.md

+# Tool Calling with Dynamo
+
+You can connect Dynamo to external tools and services using function calling (also known as tool calling). By providing a list of available functions, Dynamo can choose
+to output function arguments for the relevant function(s) which you can execute to augment the prompt with relevant external information.
+
+Tool calling (AKA function calling) is controlled using the `tool_choice` and `tools` request parameters.
+
+
+## Prerequisites
+
+To enable this feature, you should set the following flag while launching the backend worker
+
+- `--dyn-tool-call-parser` : select the parser from the available parsers list using the below command
+
+```bash
+# <backend> can be vllm, sglang, trtllm, etc. based on your installation
+python -m dynamo.<backend> --help"
+```
+
+> [!NOTE]
+> If no tool call parser is provided by the user, Dynamo will try to use default tool call parsing based on `<TOOLCALL>` and `<|python_tag|>` tool tags.
+
+> [!TIP]
+> If your model's default chat template doesn't support tool calling, but the model itself does, you can specify a custom chat template per worker
+> with `python -m dynamo.<backend> --custom-jinja-template </path/to/template.jinja>`.
+
+
+Parser to Model Mapping
+
+| Parser Name | Supported Models                                                      |
+|-------------|-----------------------------------------------------------------------|
+| hermes      | Qwen/Qwen2.5-*, Qwen/QwQ-32B, NousResearch/Hermes-2-Pro-*, NousResearch/Hermes-2-Theta-*, NousResearch/Hermes-3-* |
+| mistral | mistralai/Mistral-7B-Instruct-v0.3, Additional mistral function-calling models are compatible as well.|
+| llama3_json | meta-llama/Llama-3.1-*, meta-llama/Llama-3.2-* |
+| harmony | openai/gpt-oss-* |
+| nemotron_deci | nvidia/nemotron-* |
+| phi4 | Phi-4-* |
+| deepseek_v3_1 | deepseek-ai/DeepSeek-V3.1 |
+| pythonic |  meta-llama/Llama-4-* |
+
+
+## Examples
+
+### Launch Dynamo Frontend and Backend
+
+```bash
+# launch backend worker
+python -m dynamo.vllm --model openai/gpt-oss-20b --dyn-tool-call-parser harmony
+
+# launch frontend worker
+python -m dynamo.frontend
+```
+
+### Tool Calling Request Examples
+
+- Example 1
+```python
+from openai import OpenAI
+import json
+
+client = OpenAI(base_url="http://localhost:8081/v1", api_key="dummy")
+
+def get_weather(location: str, unit: str):
+    return f"Getting the weather for {location} in {unit}..."
+tool_functions = {"get_weather": get_weather}
+
+tools = [{
+    "type": "function",
+    "function": {
+        "name": "get_weather",
+        "description": "Get the current weather in a given location",
+        "parameters": {
+            "type": "object",
+            "properties": {
+                "location": {"type": "string", "description": "City and state, e.g., 'San Francisco, CA'"},
+                "unit": {"type": "string", "enum": ["celsius", "fahrenheit"]}
+            },
+            "required": ["location", "unit"]
+        }
+    }
+}]
+
+response = client.chat.completions.create(
+    model="openai/gpt-oss-20b",
+    messages=[{"role": "user", "content": "What's the weather like in San Francisco in Celsius?"}],
+    tools=tools,
+    tool_choice="auto",
+    max_tokens=10000
+)
+print(f"{response}")
+tool_call = response.choices[0].message.tool_calls[0].function
+print(f"Function called: {tool_call.name}")
+print(f"Arguments: {tool_call.arguments}")
+print(f"Result: {tool_functions[tool_call.name](**json.loads(tool_call.arguments))}")
+```
+
+- Example 2
+```python
+
+# Use tools defined in example 1
+
+time_tool = {
+    "type": "function",
+    "function": {
+        "name": "get_current_time_nyc",
+        "description": "Get the current time in NYC.",
+        "parameters": {}
+    }
+}
+
+
+tools.append(time_tool)
+
+messages = [
+    {"role": "user", "content": "What's the current time in New York?"}
+]
+
+
+response = client.chat.completions.create(
+    model="openai/gpt-oss-20b", #client.models.list().data[1].id,
+    messages=messages,
+    tools=tools,
+    tool_choice="auto",
+    max_tokens=100,
+)
+print(f"{response}")
+tool_call = response.choices[0].message.tool_calls[0].function
+print(f"Function called: {tool_call.name}")
+print(f"Arguments: {tool_call.arguments}")
+```
+
+- Example 3
+
+
+```python
+
+tools = [
+    {
+        "type": "function",
+        "function": {
+            "name": "get_tourist_attractions",
+            "description": "Get a list of top tourist attractions for a given city.",
+            "parameters": {
+                "type": "object",
+                "properties": {
+                    "city": {
+                        "type": "string",
+                        "description": "The name of the city to find attractions for.",
+                    }
+                },
+                "required": ["city"],
+            },
+        },
+    },
+]
+
+def get_messages():
+    return [
+        {
+            "role": "user",
+            "content": (
+                "I'm planning a trip to Tokyo next week. what are some top tourist attractions in Tokyo? "
+            ),
+        },
+    ]
+
+
+messages = get_messages()
+
+response = client.chat.completions.create(
+    model="openai/gpt-oss-20b",
+    messages=messages,
+    tools=tools,
+    tool_choice="auto",
+    max_tokens=100,
+)
+print(f"{response}")
+tool_call = response.choices[0].message.tool_calls[0].function
+print(f"Function called: {tool_call.name}")
+print(f"Arguments: {tool_call.arguments}")
+```

docs/hidden_toctree.rst

@@ -36,6 +36,7 @@
    guides/metrics.md
    guides/run_kvbm_in_vllm.md
    guides/run_kvbm_in_trtllm.md
+   guides/tool_calling.md
 
    architecture/kv_cache_routing.md
    architecture/load_planner.md