unclecode/crawl4ai · error · TypeError

{cls.__name__}.run must be async

Error message

{cls.__name__}.run must be async

What it means

Error "{cls.__name__}.run must be async" thrown in unclecode/crawl4ai.

Source

Thrown at crawl4ai/hub.py:35

    async def run(self, url: str = "", **kwargs) -> str:
        """
        Implement this method to return JSON string.
        Must accept URL + arbitrary kwargs for flexibility.
        """
        pass

    def __init_subclass__(cls, **kwargs):
        """Enforce interface validation on subclassing"""
        super().__init_subclass__(**kwargs)
        
        # Verify run method signature
        run_method = cls.run
        if not run_method.__code__.co_argcount >= 2:  # self + url
            raise TypeError(f"{cls.__name__} must implement 'run(self, url: str, **kwargs)'")
            
        # Verify async nature
        if not inspect.iscoroutinefunction(run_method):
            raise TypeError(f"{cls.__name__}.run must be async")

class CrawlerHub:
    _crawlers: Dict[str, Type[BaseCrawler]] = {}

    @classmethod
    def _discover_crawlers(cls):
        """Dynamically load crawlers from /crawlers in 3 lines"""
        base_path = Path(__file__).parent / "crawlers"
        for crawler_dir in base_path.iterdir():
            if crawler_dir.is_dir():
                try:
                    module = importlib.import_module(
                        f"crawl4ai.crawlers.{crawler_dir.name}.crawler"
                    )
                    for attr in dir(module):
                        cls._maybe_register_crawler(
                            getattr(module, attr), crawler_dir.name
                        )

View on GitHub (pinned to 7e80152142)

Solutions

1. Declare the run method with async def so it can be awaited by the hub.
2. Remove blocking synchronous calls from run or wrap them with asyncio.to_thread.

Example fix

async def run(self, url: str, **kwargs): ...

When it happens

Trigger: Thrown at crawl4ai/hub.py:35 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of unclecode/crawl4ai@7e80152142 (2026-08-14). Data as JSON: /api/errors/6cdb14ab5b5ae1e3. Report an issue: GitHub.