huggingface/smolagents · error · ValueError

Unsupported engine: {self.engine}

Error message

Unsupported engine: {self.engine}

What it means

Raised by SearchEngineTool.search when self.engine is not one of 'duckduckgo', 'bing', or 'exa'. It is the terminal else of the engine dispatch — any other engine string is rejected at search time (not construction time), which is a common surprise.

Source

Thrown at src/smolagents/default_tools.py:367

        super().__init__()
        self.max_results = max_results
        self.engine = engine

    def forward(self, query: str) -> str:
        results = self.search(query)
        if len(results) == 0:
            raise Exception("No results found! Try a less restrictive/shorter query.")
        return self.parse_results(results)

    def search(self, query: str) -> list:
        if self.engine == "duckduckgo":
            return self.search_duckduckgo(query)
        elif self.engine == "bing":
            return self.search_bing(query)
        elif self.engine == "exa":
            return self.search_exa(query)
        else:
            raise ValueError(f"Unsupported engine: {self.engine}")

    def parse_results(self, results: list) -> str:
        return "## Search Results\n\n" + "\n\n".join(
            [f"[{result['title']}]({result['link']})\n{result['description']}" for result in results]
        )

    def search_duckduckgo(self, query: str) -> list:
        import requests

        response = requests.get(
            "https://lite.duckduckgo.com/lite/",
            params={"q": query},
            headers={"User-Agent": "Mozilla/5.0"},
        )
        response.raise_for_status()
        parser = self._create_duckduckgo_parser()
        parser.feed(response.text)
        return parser.results

View on GitHub (pinned to 30bb116109)

Solutions

1. Use exactly 'duckduckgo', 'bing', or 'exa' as the engine value.
2. Validate the engine at construction time in your own wrapper (see exampleFix) so it fails fast.

Example fix

# before
tool = SearchEngineTool(engine='google'); tool.run('x')
# after
VALID = {'duckduckgo','bing','exa'}
assert tool.engine in VALID, f'engine must be one of {VALID}'
tool = SearchEngineTool(engine='exa')

VALID = {'duckduckgo','bing','exa'}
assert engine in VALID, f'engine must be one of {sorted(VALID)}'

When it happens

Trigger: Constructing SearchEngineTool(engine='google') or any misspelled engine value ('DuckDuckGo', 'exaa') and then calling search/forward — the constructor accepts it, the error only appears on first search.

Common situations: Assuming Google support, case mismatches, or validating config at construction and being surprised the error surfaces later during agent runs.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• Only 'markdown' is supported for a string argument to `code_
• Unsupported model type: {model_type}
• Tool {tool_name} is not recognized either as a default tool
• Unsupported action type: {action_type}
• You must install package `ddgs` to run this tool: for instan

AI-assisted analysis of huggingface/smolagents@30bb116109 (2026-08-28). Data as JSON: /api/errors/52d7ca95da8d7912. Report an issue: GitHub.