What causes "No response" in BoundaryML/baml?

Check upstream LLM call errors/logs — the actual failure happened before a response was produced

BoundaryML/baml · error · anyhow::Error

No response

Error message

No response

What it means

status() found neither an expr-function response, nor a function response, nor any result with constraints on the FunctionResult, so there is nothing to report and the test fails with a bare "No response". This means the test never produced any response object at all.

Solutions

Check upstream LLM call errors/logs — the actual failure happened before a response was produced
Verify the function ran to completion and its result was awaited/stored before calling status()
Inspect API key/network/timeout errors that abort the call before any response is recorded
Re-run the test; if persistent, run with verbose BAML logs

Defensive patterns

Strategy: retry

Validate before calling

// confirm a response exists before reading status
if (!result || (!result.function_response && !result.expr_function_response)) {
  throw new Error('no function response recorded yet');
}

Type guard

const hasResponse = (r) => r != null && ('function_response' in r || 'expr_function_response' in r);

Try / catch

try {
  const status = testResult.status();
} catch (e) {
  if (String(e).includes('No response')) {
    // inspect upstream LLM errors: keys, network, timeouts
  }
  throw e;
}

Prevention

Always await the function call fully before inspecting test status
Check API keys, network, and timeout settings before running tests
Log upstream LLM errors so "No response" never masks the real cause

When it happens

Trigger: Calling status() on a FunctionResult where expr_function_response is None, function_response is None, or function_response exists but result_with_constraints() returns None (no parsed result recorded).

Common situations: The LLM call never completed or was cancelled before a response was stored; the function errored before parsing so no parsed value was attached; async test orchestration read the result too early.

Related errors

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/ccfcd38c7cae5e76. Report an issue: GitHub.

Appendix: source

Thrown at engine/baml-runtime/src/types/response.rs:492

                            } else {
                                TestStatus::Pass
                            }
                        }
                    }
                } else {
                    let err = parsed.as_ref().unwrap_err();
                    match err.downcast_ref::<crate::errors::ExposedError>() {
                        Some(ExposedError::FinishReasonError { .. }) => {
                            TestStatus::Fail(TestFailReason::TestFinishReasonFailed(err))
                        }
                        _ => TestStatus::Fail(TestFailReason::TestParseFailure(err)),
                    }
                }
            } else {
                TestStatus::Fail(TestFailReason::TestLLMFailure(func_res.llm_response()))
            }
        } else {
            TestStatus::Fail(TestFailReason::TestUnspecified(anyhow::anyhow!(
                "No response"
            )))
        }
    }
}

impl std::fmt::Display for TestFailReason<'_> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::TestUnspecified(e) => write!(f, "{e}"),
            Self::TestLLMFailure(r) => write!(f, "{r}"),
            Self::TestParseFailure(e) => write!(f, "{e}"),
            Self::TestFinishReasonFailed(e) => write!(f, "{e}"),
            Self::TestConstraintsFailure {
                checks,
                failed_assert,
            } => {
                for (check, pass) in checks {

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