agentscope-ai/agentscope · error · ValueError

The field ` ` already exists in the original function…

Error message

The field `{key}` already exists in the original function schema of `{self.tool.name}`. Try to use a different name.

What it means

Raised in ToolMetadata.get_tool_schema when merging an extended model's schema into the tool's original function schema and a property name collides with one already defined on the original function parameters. Extended models are meant to add new fields, not redefine existing ones.

Solutions

1. Rename the conflicting field on the extended BaseModel to something not used by the function signature
2. Strip/alias the overlapping function parameter or the model field
3. Audit field names: set(model.model_fields) vs the function's parameter names before merging

Example fix

# before
class Ext(BaseModel):
    query: str  # collides with function arg `query`
tool_meta.get_tool_schema(extended_model=Ext)
# after
class Ext(BaseModel):
    context_query: str
tool_meta.get_tool_schema(extended_model=Ext)

import inspect
fn_params = set(inspect.signature(func).parameters)
collisions = fn_params & set(ExtendedModel.model_fields)
assert not collisions, f'field name collisions: {collisions}'

When it happens

Trigger: Calling get_tool_schema(extended_model=SomeModel) where SomeModel has a field whose name matches a parameter of the wrapped function, e.g. the function has an 'offset' parameter and the extended model also defines 'offset'.

Common situations: Adding metadata fields (session_id, user_id, memory) via an extended BaseModel whose field names clash with existing function args; reusing a generic Context model across multiple tools.

Related errors

• The $defs key ` ` conflicts with existing definition in…
• Invalid input_schema
• Exactly one of `data` or `url` must be provided.
• Invalid structured output from model
• MCPClient name ' ' contains characters not allowed by LLM…

AI-assisted analysis of agentscope-ai/agentscope@e90f1c7592 (2026-08-28). Data as JSON: /api/errors/e66118fdc581158a. Report an issue: GitHub.

Appendix: source

Thrown at src/agentscope/tool/_types.py:100

                "description": self.tool.description,
                "parameters": input_schema,
            },
        }

        extended_model = extended_model or self.extended_model

        if extended_model is None:
            return function_schema

        # Merge the extended model with the original JSON schema
        extended_schema = extended_model.model_json_schema()

        _remove_title_field(extended_schema)

        # Merge properties from extended schema
        for key, value in extended_schema["properties"].items():
            if key in function_schema["function"]["parameters"]["properties"]:
                raise ValueError(
                    f"The field `{key}` already exists in the original "
                    f"function schema of `{self.tool.name}`. Try to use a "
                    "different name.",
                )

            function_schema["function"]["parameters"]["properties"][
                key
            ] = value

            if key in extended_schema.get("required", []):
                if "required" not in function_schema["function"]["parameters"]:
                    function_schema["function"]["parameters"]["required"] = []
                function_schema["function"]["parameters"]["required"].append(
                    key,
                )

        # Merge $defs from extended schema to support nested models
        if "$defs" in extended_schema:

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