ComposioHQ/composio · error · ValidationError

{context}: slug "{tool_slug}" is too long. With prefix "{pre

Error message

{context}: slug "{tool_slug}" is too long. With prefix "{prefix}", the final slug would be {final_length} characters (max {MAX_SLUG_LENGTH}). Shorten the slug to at most {available} characters.

What it means

Raised when a custom tool's slug, after Composio prepends the LOCAL_ + TOOLKIT_ routing prefix, would exceed MAX_SLUG_LENGTH. The final routed name must fit the length cap, so the user slug alone must be short enough.

Source

Thrown at python/composio/core/models/custom_tool.py:125

def _compute_final_slug_length(tool_slug: str, toolkit_slug: t.Optional[str]) -> int:
    """Compute the final slug length: LOCAL_[TOOLKIT_]SLUG."""
    length = len(LOCAL_TOOL_PREFIX) + len(tool_slug)
    if toolkit_slug:
        length += len(toolkit_slug) + 1  # +1 for underscore separator
    return length


def _validate_slug_length(
    tool_slug: str, toolkit_slug: t.Optional[str], context: str
) -> None:
    """Validate that the final slug won't exceed the max length."""
    final_length = _compute_final_slug_length(tool_slug, toolkit_slug)
    if final_length > MAX_SLUG_LENGTH:
        prefix = LOCAL_TOOL_PREFIX + (
            f"{toolkit_slug.upper()}_" if toolkit_slug else ""
        )
        available = MAX_SLUG_LENGTH - len(prefix)
        raise ValidationError(
            f'{context}: slug "{tool_slug}" is too long. '
            f'With prefix "{prefix}", the final slug would be {final_length} '
            f"characters (max {MAX_SLUG_LENGTH}). "
            f"Shorten the slug to at most {available} characters."
        )


def _build_final_slug(tool_slug: str, toolkit_slug: t.Optional[str] = None) -> str:
    """Build the final slug: LOCAL_[TOOLKIT_]SLUG."""
    upper = tool_slug.upper()
    if toolkit_slug:
        return f"{LOCAL_TOOL_PREFIX}{toolkit_slug.upper()}_{upper}"
    return f"{LOCAL_TOOL_PREFIX}{upper}"


def _get_input_json_schema(model: t.Type[BaseModel]) -> t.Dict[str, t.Any]:
    """Convert a Pydantic model class to a JSON Schema dict suitable for the backend."""
    full_schema = model.model_json_schema()

View on GitHub (pinned to 64b1b85502)

Solutions

1. Shorten the tool slug to the reported `available` character count (the error message tells you the exact budget)
2. Shorten the toolkit slug too — it reduces the prefix length and frees characters for the tool slug
3. When generating slugs programmatically, truncate to a safe bound before tool creation

Example fix

# before
@tool(slug="perform_advanced_semantic_search_across_all_connected_user_documents")

# after
@tool(slug="semantic_doc_search")

from composio.core.models.custom_tool import MAX_SLUG_LENGTH, LOCAL_TOOL_PREFIX
def fits(slug: str, toolkit_slug: str = "") -> bool:
    prefix = LOCAL_TOOL_PREFIX + (f"{toolkit_slug.upper()}_" if toolkit_slug else "")
    return len(prefix) + len(slug) <= MAX_SLUG_LENGTH
def clip(slug: str, toolkit_slug: str = "") -> str:
    prefix = LOCAL_TOOL_PREFIX + (f"{toolkit_slug.upper()}_" if toolkit_slug else "")
    return slug[: MAX_SLUG_LENGTH - len(prefix)]

def slug_fits(slug: str, toolkit_slug: str) -> bool:
    prefix = "LOCAL_" + (toolkit_slug.upper() + "_" if toolkit_slug else "")
    return len(prefix + slug) <= 64  # verify MAX_SLUG_LENGTH for your version

try:
    Tool(slug=slug, ...)
except ValidationError:
    Tool(slug=slug[:40], ...)

When it happens

Trigger: Creating a tool with a very long slug (and/or a long toolkit slug) such that len('LOCAL_<TOOLKIT>_<slug>') > MAX_SLUG_LENGTH, via the @tool decorator, Tool(), or toolkit.tool(...).

Common situations: Auto-generating slugs from verbose function or docstring titles; long toolkit names eating the budget; machine-generated descriptive slugs from LLM pipelines.

Related errors

• {context}: slug is required
• {context}: slug must only contain alphanumeric characters, u
• Could not determine a home directory to store the Composio c
• Cache directory {directory} is not writable please provide a
• module {__name__!r} has no attribute {name!r}

AI-assisted analysis of ComposioHQ/composio@64b1b85502 (2026-08-28). Data as JSON: /api/errors/fab26328430d0491. Report an issue: GitHub.