BoundaryML/baml · error

LLM function not found: {}: {}

Error message

LLM function not found: {}: {}

What it means

Before invoking a function through the async interpreter runtime, the runtime looks up the function name in the IR. If `find_function` fails, the name doesn't exist in the loaded BAML project, and the error includes the underlying lookup error detail.

Source

Thrown at engine/baml-runtime/src/async_interpreter_runtime.rs:265

            move |fn_name: String,
                  args: Vec<BamlValue>,
                  watch_context: Option<WatchStreamContext>| {
                let llm_runtime = Arc::clone(&llm_runtime_clone);
                let ctx = ctx_clone.clone();
                let tb = tb_clone.clone();
                let cb = cb_clone.clone();
                let env_vars = env_vars_clone.clone();
                let cancel_tripwire = cancel_tripwire_clone.clone();
                let watch_handler: SharedWatchHandler = Arc::clone(&watch_handler_for_llm);
                let parent_fn = parent_function_name.clone();
                let tags = tags_clone.clone();
                #[cfg(not(target_arch = "wasm32"))]
                let tokio_rt = tokio_runtime.clone();

                async move {
                    // Find the LLM function to get parameter names
                    let llm_fn = llm_runtime.ir().find_function(&fn_name).map_err(|e| {
                        anyhow::anyhow!("LLM function not found: {}: {}", fn_name, e)
                    })?;

                    // Convert args to parameter map
                    let llm_params = args
                        .into_iter()
                        .zip(llm_fn.inputs().iter().map(|(name, _)| name.clone()))
                        .map(|(arg, param_name)| (param_name, arg))
                        .collect::<BamlMap<_, _>>();

                    // Check if we should use streaming with watch notifications
                    if let Some(watch_ctx) = watch_context {
                        // Use streaming with watch notifications
                        let tracer = llm_runtime.tracer_wrapper.get_or_create_tracer(&env_vars);

                        // Create RuntimeContext from RuntimeContextManager
                        let runtime_ctx = ctx.create_ctx(
                            tb.as_ref(),
                            cb.as_ref(),

View on GitHub (pinned to bd85ce9dee)

Solutions

  1. Verify the function name matches a function declared in your .baml files (exact spelling/case).
  2. Ensure all .baml files containing the function are included in the runtime's loaded sources.
  3. Regenerate/reload the runtime after adding new functions so the IR is current.

Example fix

// before
runtime.call_function("ClassifgyIntent", args)
// after
runtime.call_function("ClassifyIntent", args)
Defensive patterns

Strategy: validation

Validate before calling

// Rust: check before calling
if llm_runtime.ir().find_function(fn_name).is_err() {
    eprintln!("function '{fn_name}' is not defined in loaded BAML sources");
    return;
}

Try / catch

match runtime.call_function(fn_name, args).await {
    Ok(v) => v,
    Err(e) if e.to_string().contains("LLM function not found") => {
        eprintln!("Unknown function '{fn_name}': {e:#}");
        Default::default()
    }
    Err(e) => return Err(e),
}

Prevention

When it happens

Trigger: call_function (via call_function_sync) with an fn_name that has no matching function in the compiled BAML IR.

Common situations: Typos in the function name, calling a function defined in a .baml file that wasn't loaded/compiled, or calling an expression function where only an LLM function lookup path is taken.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/1222c75485d0fc15. Report an issue: GitHub.