What causes "Error while generating output: {e}" in huggingface/smolagents?

Inspect the chained cause (`raise ... from e` — read the full traceback) to identify the underlying provider error.

huggingface/smolagents · error · AgentGenerationError

Error while generating output: {e}

Error message

Error while generating output:
{e}

What it means

Inside ToolCallingAgent._step_stream, any exception raised by model.generate() while producing the chat completion is wrapped in AgentGenerationError. The original exception is chained (raise ... from e), so the traceback retains the root cause — typically provider API errors, auth failures, rate limits, or malformed responses.

Source

Thrown at src/smolagents/agents.py:1325

                chat_message = agglomerate_stream_deltas(chat_message_stream_deltas)
            else:
                chat_message: ChatMessage = self.model.generate(
                    input_messages,
                    stop_sequences=["Observation:", "Calling tools:"],
                    tools_to_call_from=self.tools_and_managed_agents,
                )
                self.logger.log_markdown(
                    content=str(chat_message.content or chat_message.raw or ""),
                    title="Output message of the LLM:",
                    level=LogLevel.DEBUG,
                )

            # Record model output
            memory_step.model_output_message = chat_message
            memory_step.model_output = chat_message.content
            memory_step.token_usage = chat_message.token_usage
        except Exception as e:
            raise AgentGenerationError(f"Error while generating output:\n{e}", self.logger) from e

        if chat_message.tool_calls is None or len(chat_message.tool_calls) == 0:
            try:
                chat_message = self.model.parse_tool_calls(chat_message)
            except Exception as e:
                raise AgentParsingError(f"Error while parsing tool call from model output: {e}", self.logger)
        else:
            for tool_call in chat_message.tool_calls:
                tool_call.function.arguments = parse_json_if_needed(tool_call.function.arguments)
        final_answer, got_final_answer = None, False
        for output in self.process_tool_calls(chat_message, memory_step):
            yield output
            if isinstance(output, ToolOutput):
                if output.is_final_answer:
                    if len(chat_message.tool_calls) > 1:
                        raise AgentExecutionError(
                            "If you want to return an answer, please do not perform any other tool calls than the final answer tool call!",
                            self.logger,

View on GitHub (pinned to 30bb116109)

Solutions

Inspect the chained cause (`raise ... from e` — read the full traceback) to identify the underlying provider error.
Fix the root cause: valid API key, correct base_url, sufficient quota/limits.
Wrap agent.run in retry logic (e.g. tenacity) for transient 429/5xx provider errors.

Defensive patterns

Strategy: retry

Try / catch

from smolagents.exceptions import AgentGenerationError

try:
    result = agent.run(task)
except AgentGenerationError as e:
    cause = e.__cause__  # inspect underlying provider error
    if 'rate limit' in str(cause).lower():
        time.sleep(30)
        result = agent.run(task)
    else:
        raise

Prevention

Validate provider credentials and quota before starting long agent runs.
Wrap runs in retry with exponential backoff for transient provider errors.
Log e.__cause__ to distinguish provider failures from agent logic errors.

When it happens

Trigger: Running agent.run(...) / agent.step(...) with stream_outputs where self.model.generate() raises: expired API key, network timeout, 429 rate limit, or a provider returning an unexpected payload.

Common situations: Long agent runs that exhaust token/rate limits; invalid or missing OPENAI_API_KEY-style env vars; transient network failures to the LLM provider; provider API schema changes between library versions.

Related errors

AI-assisted analysis of huggingface/smolagents@30bb116109 (2026-08-28). Data as JSON: /api/errors/8ebf795f76aa4389. Report an issue: GitHub.