Feature GuidesTool Calling & Reasoning Parsing

Parser Configuration

How —dyn-chat-processor, —dyn-tool-call-parser, and —dyn-reasoning-parser fit together

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Dynamo turns a model’s raw tool-call and reasoning markup into structured tool_calls and reasoning_content. Two independent choices control how that parsing happens. This page is the single source of truth for which flags combine and which combinations don’t make sense. For the parser names themselves, follow the per-stage links at the bottom.

The choices

1. Who parses — --dyn-chat-processor (a frontend flag; default dynamo):

  • dynamo (default) — Dynamo’s framework-agnostic Rust parser. Works on every backend (vLLM, SGLang, TRT-LLM) and with disaggregated serving.
  • vllm / sglang — delegate parsing to that engine’s own Python parser (“engine fallback”). Use only when Dynamo does not ship a parser for your model.

2. Which parser — the flag name and where it goes depend on choice 1:

Parser ImplementationParser flag(s) and where they goParses withDisaggregated servingBackends
dynamo (default)--dyn-tool-call-parser <name> and/or --dyn-reasoning-parser <name> — on the workerDynamo Rust frontendSupportedvLLM, SGLang, TRT-LLM
vllm--tool-call-parser <name> and/or --reasoning-parser <name> — on the frontendvLLM PythonSupportedvLLM
sglang--tool-call-parser <name> and/or --reasoning-parser <name> — on the frontendSGLang PythonSupportedSGLang

The pairing rule

  • The --dyn-* parser flags pair with the dynamo chat processor and go on the worker: --dyn-tool-call-parser, --dyn-reasoning-parser.
  • The bare --tool-call-parser / --reasoning-parser flags pair with vllm / sglang and go on the frontend.

Tool calling and reasoning are independent — set one, the other, or both — but always from the same family as your chat processor. You never mix the two families.

What does NOT make sense

CombinationWhy it’s wrong
--dyn-chat-processor dynamo + --tool-call-parser / --reasoning-parserThe bare flags drive the engine-fallback path; the default Dynamo path uses the --dyn- flags. Use --dyn-tool-call-parser / --dyn-reasoning-parser.
--dyn-chat-processor vllm/sglang + --dyn-tool-call-parser / --dyn-reasoning-parserThe --dyn- flags only drive Dynamo’s native parser; an engine processor reads its own --tool-call-parser / --reasoning-parser.
--dyn-chat-processor vllm/sglang on TRT-LLMTRT-LLM engine fallback is a work in progress. Use the default dynamo processor.
Reusing a parser name across familiesThe registries differ — e.g. Dynamo deepseek_v3 vs vLLM/SGLang deepseekv3, Dynamo nemotron3 vs vLLM nemotron_v3. Use the name from the registry that matches your chat processor.

Examples

Default (Dynamo-native) — the common case. The same --dyn-* flags work on every backend; pick one worker. The chat processor defaults to dynamo, so the frontend flag is optional:

$# Frontend — chat processor defaults to `dynamo`, so these two are identical:
$python -m dynamo.frontend
$python -m dynamo.frontend --dyn-chat-processor dynamo
$
$# Worker selects the Dynamo parsers — same flags on vLLM, SGLang, or TRT-LLM:
$python -m dynamo.vllm   --model Qwen/Qwen3-0.6B \
>  --dyn-tool-call-parser hermes --dyn-reasoning-parser qwen3
$python -m dynamo.sglang --model Qwen/Qwen3-0.6B \
>  --dyn-tool-call-parser hermes --dyn-reasoning-parser qwen3
$python -m dynamo.trtllm --model-path Qwen/Qwen3-0.6B --served-model-name Qwen/Qwen3-0.6B \
>  --dyn-tool-call-parser hermes --dyn-reasoning-parser qwen3

Engine fallback — only when Dynamo lacks a parser for your model. Supported on vLLM and SGLang (not TRT-LLM); the parser flags go on the frontend and use the engine’s own parser names:

$# vLLM chat processor — frontend carries the parser flags, then launch the worker:
$python -m dynamo.frontend --dyn-chat-processor vllm   --tool-call-parser hermes  --reasoning-parser qwen3
$python -m dynamo.vllm   --model Qwen/Qwen3-0.6B
$
$# SGLang chat processor
$python -m dynamo.frontend --dyn-chat-processor sglang --tool-call-parser qwen25  --reasoning-parser qwen3
$python -m dynamo.sglang --model Qwen/Qwen3-0.6B

Parser names and per-stage details