BoundaryML/baml · error

baml.media.image.from_url expects 1 argument, got {} at {:?}

Error message

baml.media.image.from_url expects 1 argument, got {} at {:?}

What it means

Thrown by the BAML interpreter's builtin-function evaluator when `baml.media.image.from_url` is called with an argument count other than exactly 1. The builtin constructs an image BamlMedia from a URL and requires exactly one string argument.

Source

Thrown at engine/baml-compiler/src/thir/interpret.rs:2716

                }
                Ok(BamlValueWithMeta::Map(baml_map, meta.clone()))
            }
        }
    }

    json_to_baml(&json_value, target_type, meta)
}

async fn evaluate_builtin_function(
    fn_name: &str,
    args: &[BamlValueWithMeta<ExprMetadata>],
    type_args: &[baml_types::TypeIR],
    meta: &ExprMetadata,
) -> Result<BamlValueWithMeta<ExprMetadata>> {
    match fn_name {
        "baml.media.image.from_url" => {
            if args.len() != 1 {
                bail!(
                    "baml.media.image.from_url expects 1 argument, got {} at {:?}",
                    args.len(),
                    meta.0
                );
            }
            let url = match &args[0] {
                BamlValueWithMeta::String(s, _) => s.clone(),
                _ => bail!(
                    "baml.media.image.from_url expects a string argument at {:?}",
                    meta.0
                ),
            };
            Ok(BamlValueWithMeta::Media(
                baml_types::BamlMedia::url(baml_types::BamlMediaType::Image, url, None),
                meta.clone(),
            ))
        }
        "baml.fetch_as" => {

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Call baml.media.image.from_url with exactly one string URL argument
2. Move any extra configuration (headers, alt text) out of the builtin call; it only accepts a URL
3. Check arity at the call site; count arguments if they are generated dynamically (e.g. spread from a list)
4. Consult the builtin registry for media builtins that accept extra parameters if you need them

Example fix

// before (BAML)
let img = baml.media.image.from_url(url, "logo");
// after
let img = baml.media.image.from_url(url);

function validateImageFromUrlArgs(args: unknown[]): void {
  if (args.length !== 1) {
    throw new Error(`baml.media.image.from_url expects 1 argument, got ${args.length}`);
  }
  if (typeof args[0] !== 'string') {
    throw new Error('baml.media.image.from_url expects a string URL');
  }
}

try {
  img = evaluate(call);
} catch (e) {
  if (String(e).includes('baml.media.image.from_url expects 1 argument')) {
    // trim extra args at the call site
  }
  throw e;
}

When it happens

Trigger: Calling baml.media.image.from_url with 0 arguments, or with 2+ arguments (e.g. trying to pass url plus alt-text or dimensions, which this builtin does not accept).

Common situations: Copying a media-helper signature from another API that accepts options, adding extra positional parameters, or forgetting the url argument entirely when constructing dynamic media in prompt expressions.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

• env.get expects exactly one argument
• baml.media.image.from_url expects a string argument at {:?}
• baml.fetch_as expects 1 argument (url), got {} at {:?}
• env.get argument must be a string
• length() method takes no arguments at {:?}

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/8d01cd6aeb69a414. Report an issue: GitHub.