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[Frontend] Align tool_choice="required" behavior with OpenAI when tools is empty #21052

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Merged
merged 4 commits into from
Aug 1, 2025
Merged

[Frontend] Align tool_choice="required" behavior with OpenAI when tools is empty #21052

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c4e552b
[Frontend] Validate tool list length when tool_choice=required
n0gu-furiosa Jul 16, 2025
781573d
Treat tool_choice="required" and empty tools as equivalent to "none"
n0gu-furiosa Jul 17, 2025
14983e5
Merge branch 'vllm-project:main' into tools-required-validation
n0gu-furiosa Jul 29, 2025
174a22f
Merge branch 'vllm-project:main' into tools-required-validation
n0gu-furiosa Aug 1, 2025
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9 changes: 9 additions & 0 deletions vllm/entrypoints/openai/protocol.py
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Original file line number Diff line number Diff line change
Expand Up @@ -859,6 +859,15 @@ def check_tool_usage(cls, data):
'are supported.'
)

# if tool_choice is "required" but the "tools" list is empty,
# override the data to behave like "none" to align with
# OpenAI’s behavior.
if data["tool_choice"] == "required" and isinstance(
data["tools"], list) and len(data["tools"]) == 0:
data["tool_choice"] = "none"
del data["tools"]
return data

# ensure that if "tool_choice" is specified as an object,
# it matches a valid tool
correct_usage_message = 'Correct usage: `{"type": "function",' \
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