agentscope-ai/agentscope · error · TypeError

Invalid skill or loader: {_}. Must be a skill, skill loader,

Error message

Invalid skill or loader: {_}. Must be a skill, skill loader, or directory path.

What it means

ToolGroup.__init__ validates each item in skills/mcps: it must be a Skill instance, a SkillLoaderBase, or a string directory path; anything else raises TypeError naming the offending object.

Source

Thrown at src/agentscope/tool/_tool_group.py:94

            )

        self.name = name
        self.description = description or ""
        self.instructions = instructions
        self.tools = tools or []
        self.mcps = mcps or []

        # Skill
        self.skills_or_loaders = []
        for _ in skills_or_loaders or []:
            if isinstance(_, str):
                self.skills_or_loaders.append(LocalSkillLoader(directory=_))

            elif isinstance(_, (Skill, SkillLoaderBase)):
                self.skills_or_loaders.append(_)

            else:
                raise TypeError(
                    f"Invalid skill or loader: {_}. Must be a skill, "
                    f"skill loader, or directory path.",
                )

    async def list_skills(self) -> list[Skill]:
        """List all the skills in this tool group."""
        skills = []
        for skill_or_loader in self.skills_or_loaders:
            if isinstance(skill_or_loader, Skill):
                skills.append(skill_or_loader)
            elif isinstance(skill_or_loader, SkillLoaderBase):
                skills.extend(await skill_or_loader.list_skills())

        return skills

View on GitHub (pinned to e90f1c7592)

Solutions

1. Convert Path to str: str(path)
2. Instantiate skills: Skill(...) rather than the class
3. Ensure custom loaders subclass SkillLoaderBase from the installed agentscope version

Example fix

# before
ToolGroup(name='x', description='d', skills=[Path('./skills')])
# after
ToolGroup(name='x', description='d', skills=['./skills'])

from pathlib import Path
items = [str(i) if isinstance(i, Path) else i for i in skills]

from agentscope.tool import Skill, SkillLoaderBase
def valid_skill_item(o) -> bool:
    return isinstance(o, str) or isinstance(o, (Skill, SkillLoaderBase))

When it happens

Trigger: Passing a module, a class instead of an instance, a Path object, or an arbitrary object in the skills list.

Common situations: Passing pathlib.Path instead of str; passing Skill (class) rather than Skill(...); passing a loader from an incompatible version with a different base class.

Understand the failure class

Background: Invalid argument type errors: "must be of type string", "expected X, got Y", and ERR_INVALID_ARG_TYPE explained — this error's family across 15 libraries.

Related errors

• Input must be a list of Msg objects.
• Expected Msg object, got {type(msg)} instead.
• The tool group description is required for tool group '{name
• Invalid logging level: {level}. Must be one of 'INFO', 'DEBU
• factory must be a callable, got {type(factory).__name__}

AI-assisted analysis of agentscope-ai/agentscope@e90f1c7592 (2026-08-28). Data as JSON: /api/errors/d2e943960754e052. Report an issue: GitHub.