Tool Call Parsing (Dynamo)

Connect Dynamo to external tools and services using Dynamo’s built-in tool call parsers

You can connect Dynamo to external tools and services using 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 is controlled using the tool_choice and tools request parameters.

This page covers parser names for the default Dynamo-native path. If Dynamo does not list a parser for your model, see Parser Engine Fallback. For how --dyn-tool-call-parser combines with --dyn-chat-processor and --dyn-reasoning-parser (and which combinations are invalid), see Parser Configuration.

Prerequisites

To enable this feature, you should set the following flag while launching the backend worker

--dyn-tool-call-parser: select the tool call parser from the supported list below

$ # <backend> can be sglang, trtllm, vllm, etc. based on your installation
$ python -m dynamo.<backend> --help

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>.

If your model also emits reasoning content that should be separated from normal output, see Reasoning Parsing (Dynamo) for the supported --dyn-reasoning-parser values.

Supported Tool Call Parsers

The table below lists the currently supported tool call parsers in Dynamo’s registry. The Upstream name column shows where the vLLM or SGLang parser name differs from Dynamo’s — relevant when using --dyn-chat-processor vllm or sglang (see Parser Engine Fallback). A blank upstream column means the same name works everywhere. Dynamo-only means no upstream parser exists for this format.

Parser Name	Models	Upstream name	Notes
`kimi_k2`	Kimi K2 Instruct/Thinking, Kimi K2.5		Pair with `--dyn-reasoning-parser kimi` or `kimi_k25`
`minimax_m2`	MiniMax M2 / M2.1	vLLM: `minimax`	XML `<minimax:tool_call>`
`deepseek_v4`	DeepSeek V4 Pro / Flash	vLLM: `deepseek_v4`; SGLang: `deepseekv4`	DSML tags (`<｜DSML｜tool_calls>...`). Aliases: `deepseek-v4`, `deepseekv4`
`deepseek_v3`	DeepSeek V3, DeepSeek R1-0528+	SGLang: `deepseekv3`	Special Unicode markers
`deepseek_v3_1`	DeepSeek V3.1	Dynamo-only	JSON separators
`deepseek_v3_2`	DeepSeek V3.2+	Dynamo-only	DSML tags (`<｜DSML｜function_calls>...`)
`qwen3_coder`	Qwen3.5, Qwen3-Coder		XML `<tool_call><function=...>`
`glm47`	GLM-4.5, GLM-4.7	Dynamo-only	XML `<arg_key>/<arg_value>`
`nemotron_deci`	Nemotron-Super / -Ultra / -Deci, Llama-Nemotron-Ultra / -Super	Dynamo-only	`<TOOLCALL>` JSON
`nemotron_nano`	Nemotron-Nano	Dynamo-only	Alias for `qwen3_coder`
`gemma4`	Google Gemma 4 (thinking models)	vLLM: `gemma4`	Custom non-JSON grammar with `<\|"\|>` string delimiters and `<\|tool_call>...<tool_call\|>` markers. Aliases: `gemma-4`. Pair with `--dyn-reasoning-parser gemma4` and `--custom-jinja-template examples/chat_templates/gemma4_tool.jinja`
`harmony`	gpt-oss-20b / -120b	Dynamo-only	Harmony channel format
`hermes`	Qwen2.5-*, QwQ-32B, Qwen3-Instruct, Qwen3-Think, NousHermes-2/3	vLLM: `qwen2_5`; SGLang: `qwen25` (for Qwen models)	`<tool_call>` JSON
`phi4`	Phi-4, Phi-4-mini, Phi-4-mini-reasoning	vLLM: `phi4_mini_json`	`functools[...]` JSON
`pythonic`	Llama 4 (Scout / Maverick)		Python-list tool syntax
`llama3_json`	Llama 3 / 3.1 / 3.2 / 3.3 Instruct		`<\|python_tag\|>` tool syntax
`mistral`	Mistral / Mixtral / Mistral-Nemo, Magistral		`[TOOL_CALLS]...[/TOOL_CALLS]`
`jamba`	Jamba 1.5 / 1.6 / 1.7	Dynamo-only	`<tool_calls>` JSON
`default`	(fallback)	Dynamo-only	Empty JSON config (no start/end tokens). Prefer a model-specific parser for production use.

For Kimi K2.5 thinking models, pair --dyn-tool-call-parser kimi_k2 with --dyn-reasoning-parser kimi_k25 from Reasoning Parsing (Dynamo) so that both <think> blocks and tool calls are parsed correctly from the same response.

Examples

Launch Dynamo Frontend and Backend

$ # launch backend worker (or dynamo.vllm)
$ python -m dynamo.sglang --model Qwen/Qwen3.5-4B --dyn-tool-call-parser qwen3_coder --dyn-reasoning-parser qwen3
$ 
$ # launch frontend worker
$ python -m dynamo.frontend

Tool Calling Request Example

$ curl -s http://localhost:8000/v1/chat/completions \
>   -H 'Content-Type: application/json' \
>   -d '{
>     "model": "Qwen/Qwen3.5-4B",
>     "messages": [
>       {"role": "user", "content": "What is the weather in San Francisco and New York?"}
>     ],
>     "tools": [{
>       "type": "function",
>       "function": {
>         "name": "get_weather",
>         "description": "Get the current weather for a location.",
>         "parameters": {
>           "type": "object",
>           "properties": {"location": {"type": "string"}},
>           "required": ["location"]
>         }
>       }
>     }],
>     "tool_choice": "auto"
>   }'

Dynamo parses the tool calls out of the model output and surfaces them as OpenAI-compatible tool_calls entries on the response:

1 {
2   "id": "chatcmpl-b415caad-9be0-4d9e-ac6d-9d23bfe57703",
3   "choices": [
4     {
5       "index": 0,
6       "message": {
7         "role": "assistant",
8         "content": null,
9         "reasoning_content": "The user is asking about the weather in two cities: San Francisco and New York. I need to call the get_weather function for each city. I'll make two separate function calls to get the weather information for both locations.\n",
10         "tool_calls": [
11           {
12             "id": "call-56223a95-3d14-4433-a94e-011f106c0e40",
13             "type": "function",
14             "function": {
15               "name": "get_weather",
16               "arguments": "{\"location\":\"San Francisco\"}"
17             }
18           },
19           {
20             "id": "call-d5b5772b-6b0c-4120-ad01-623278a937fe",
21             "type": "function",
22             "function": {
23               "name": "get_weather",
24               "arguments": "{\"location\":\"New York\"}"
25             }
26           }
27         ]
28       },
29       "finish_reason": "tool_calls",
30       "logprobs": null
31     }
32   ],
33   "created": 1778653281,
34   "model": "Qwen/Qwen3.5-4B",
35   ...
36 }

If a tool call comes back wrong, add "logprobs": true to a single repro request and share the response. See Troubleshooting Tool Calls for what to capture and include when reporting an issue.

Optional: structural tags

You can optionally turn on xgrammar structural tags so guided decoding matches the parser’s tool-call format at token granularity. See Structural tag (guided decoding for tool calls).

$	# <backend> can be sglang, trtllm, vllm, etc. based on your installation
$	python -m dynamo.<backend> --help

$	# launch backend worker (or dynamo.vllm)
$	python -m dynamo.sglang --model Qwen/Qwen3.5-4B --dyn-tool-call-parser qwen3_coder --dyn-reasoning-parser qwen3
$
$	# launch frontend worker
$	python -m dynamo.frontend

$	curl -s http://localhost:8000/v1/chat/completions \
>	-H 'Content-Type: application/json' \
>	-d '{
>	"model": "Qwen/Qwen3.5-4B",
>	"messages": [
>	{"role": "user", "content": "What is the weather in San Francisco and New York?"}
>	],
>	"tools": [{
>	"type": "function",
>	"function": {
>	"name": "get_weather",
>	"description": "Get the current weather for a location.",
>	"parameters": {
>	"type": "object",
>	"properties": {"location": {"type": "string"}},
>	"required": ["location"]
>	}
>	}
>	}],
>	"tool_choice": "auto"
>	}'

1	{
2	"id": "chatcmpl-b415caad-9be0-4d9e-ac6d-9d23bfe57703",
3	"choices": [
4	{
5	"index": 0,
6	"message": {
7	"role": "assistant",
8	"content": null,
9	"reasoning_content": "The user is asking about the weather in two cities: San Francisco and New York. I need to call the get_weather function for each city. I'll make two separate function calls to get the weather information for both locations.\n",
10	"tool_calls": [
11	{
12	"id": "call-56223a95-3d14-4433-a94e-011f106c0e40",
13	"type": "function",
14	"function": {
15	"name": "get_weather",
16	"arguments": "{\"location\":\"San Francisco\"}"
17	}
18	},
19	{
20	"id": "call-d5b5772b-6b0c-4120-ad01-623278a937fe",
21	"type": "function",
22	"function": {
23	"name": "get_weather",
24	"arguments": "{\"location\":\"New York\"}"
25	}
26	}
27	]
28	},
29	"finish_reason": "tool_calls",
30	"logprobs": null
31	}
32	],
33	"created": 1778653281,
34	"model": "Qwen/Qwen3.5-4B",
35	...
36	}