BoundaryML/baml · error

Class {} not found

Error message

Class {} not found

What it means

find_class in ScopedIR fails when the requested class name is absent from the IR and there is no RuntimeClassOverride. ScopedIR resolves names for prompt/output rendering; with neither a static definition nor a dynamic override the class cannot be resolved, so rendering aborts.

Source

Thrown at engine/baml-runtime/src/internal/prompt_renderer/scoped_ir.rs:40

}

impl<'ir> ScopedIr<'ir> {
    pub fn new(
        ir: &'ir internal_baml_core::ir::repr::IntermediateRepr,
        ctx: &'ir RuntimeContext,
    ) -> Self {
        Self { ir, ctx }
    }

    fn find_class(
        &self,
        class_name: &str,
    ) -> Result<FindResult<internal_baml_core::ir::ClassWalker<'ir>, &RuntimeClassOverride>> {
        let class_override = self.ctx.class_override.get(class_name);
        let class = self.ir.find_class(class_name);

        match (class, class_override) {
            (Err(_), None) => Err(anyhow::anyhow!("Class {} not found", class_name)),
            (Ok(class), None) => Ok(FindResult::OnlyIr(class)),
            (Err(_), Some(class_override)) => Ok(FindResult::OnlyDynamic(class_override)),
            (Ok(class), Some(class_override)) => Ok(FindResult::Overriden(class, class_override)),
        }
    }

    fn find_enum(
        &self,
        enum_name: &str,
    ) -> Result<FindResult<internal_baml_core::ir::EnumWalker<'ir>, &RuntimeEnumOverride>> {
        let enum_override = self.ctx.enum_overrides.get(enum_name);
        let r#enum = self.ir.find_enum(enum_name);

        match (r#enum, enum_override) {
            (Err(_), None) => Err(anyhow::anyhow!("Enum {} not found", enum_name)),
            (Ok(r#enum), None) => Ok(FindResult::OnlyIr(r#enum)),
            (Err(_), Some(enum_override)) => Ok(FindResult::OnlyDynamic(enum_override)),
            (Ok(r#enum), Some(enum_override)) => Ok(FindResult::Overriden(r#enum, enum_override)),

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Define the class in a .baml file within the project, or fix the name typo.
2. If the class is dynamic (tests/evals), supply a RuntimeClassOverride via the RuntimeContext.
3. Regenerate the client (baml-cli generate) so the runtime IR is current.
4. Verify the .baml file containing the class is inside the baml_src directory.

Example fix

// before
scoped.find_class("Outpt")?; // typo
// after
scoped.find_class("Output")?;

if scoped.find_class(class_name).is_err() {
    eprintln!("Class {} missing from BAML schema", class_name);
}

fn class_resolves(scoped: &ScopedIr, name: &str) -> bool {
    scoped.find_class(name).is_ok()
}

match scoped.find_class(class_name) {
    Ok(result) => render(result),
    Err(e) if e.to_string().contains("not found") => {
        // fall back to defaults or fix schema
    }
    Err(e) => return Err(e),
}

When it happens

Trigger: Calling render_output_format / prompt rendering with a class (response model) name that does not exist in any loaded .baml file and has no class override in RuntimeContext.

Common situations: Typo in the class name; class deleted or renamed; class defined in a .baml file not picked up by the BAML project; invoking a function whose output type was removed; client-side dynamic classes not passed as overrides.

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

• Enum {} not found
• Class with name {name} does not exist
• function `{function_name}` not found
• function `{target_name}` not found
• Schema inconsistency: {message}

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/749e728ef27518be. Report an issue: GitHub.