BoundaryML/baml · error · napi::Error

BamlError: Unexpected error from BAML: {err}

Error message

BamlError: Unexpected error from BAML: {err}

What it means

from_anyhow_error downcasts an anyhow error to an LLMResponse; if it is LLMResponse::Success (a success value arriving on the error path, which should be impossible), BAML throws 'BamlError: Unexpected error from BAML: <err>' with GenericFailure. This indicates an internal invariant violation in error propagation.

Source

Thrown at engine/language_client_typescript/src/errors.rs:87

                raw_response.as_deref(),
            ),
            ExposedError::AbortError {
                detailed_message, ..
            } => throw_baml_abort_error(if detailed_message.is_empty() {
                None
            } else {
                Some(detailed_message.as_str())
            }),
            ExposedError::TimeoutError {
                client_name,
                message,
            } => throw_baml_timeout_error(client_name, message),
        }
    } else if let Some(er) = err.downcast_ref::<ScopeStack>() {
        invalid_argument_error(&format!("{er}"))
    } else if let Some(er) = err.downcast_ref::<LLMResponse>() {
        match er {
            LLMResponse::Success(_) => napi::Error::new(
                napi::Status::GenericFailure,
                format!("BamlError: Unexpected error from BAML: {err}"),
            ),
            LLMResponse::LLMFailure(failed) => match &failed.code {
                baml_runtime::internal::llm_client::ErrorCode::Other(2) => napi::Error::new(
                    napi::Status::GenericFailure,
                    format!(
                        "BamlError: BamlClientError: Something went wrong with the LLM client: {}",
                        failed.message
                    ),
                ),
                baml_runtime::internal::llm_client::ErrorCode::Timeout => {
                    throw_baml_timeout_error(failed.client.as_str(), failed.message.as_str())
                }
                baml_runtime::internal::llm_client::ErrorCode::Other(_)
                | baml_runtime::internal::llm_client::ErrorCode::InvalidAuthentication
                | baml_runtime::internal::llm_client::ErrorCode::NotSupported
                | baml_runtime::internal::llm_client::ErrorCode::RateLimited

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Capture the full message and check for known issues at github.com/boundaryml/baml/issues.
2. Upgrade @boundaryml/baml and the CLI to latest and regenerate — this class of bug is often fixed in newer releases.
3. Reduce to a minimal .baml + client snippet and file a bug with the message text.

try {
  const res = await b.MyFunction(input);
} catch (e) {
  if (String(e.message).startsWith('BamlError: Unexpected error from BAML')) {
    reportToBamlIssueTracker(e.message); // internal bug, not user-fixable
  }
  throw e;
}

When it happens

Trigger: An anyhow::Error wrapping LLMResponse::Success reaches from_anyhow_error during call_function/stream_function/etc.; i.e. the runtime converted a non-error response into the error channel.

Common situations: BAML runtime bugs; unusual client configurations confusing the result plumbing; typically reported upstream rather than fixed by user code.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• BamlError: BamlClientError: Something went wrong with the LL
• VM internal error: {0}
• {self}\n\nDetailed message: {detailed_message}
• Failed before LLM call: {message}
• Operation cancelled: {message}

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/42ec0082543aba83. Report an issue: GitHub.