BoundaryML/baml · error

`{}` is not a BAML source file. Use a `.baml` file with `--f

Error message

`{}` is not a BAML source file. Use a `.baml` file with `--file`.

What it means

After confirming the --file path is a regular file, resolve_standalone_file checks its extension is `.baml`. A non-`.baml` file is rejected because --file only accepts BAML source files. This prevents compiling config files, generated code, or unrelated sources as BAML.

Source

Thrown at baml_language/crates/baml_cli/src/project_load.rs:73

        Some(reporter) => load_project_from_reporting(from, reporter)?,
        None => load_project_from(from)?,
    };
    let root = loaded.root().to_path_buf();
    Ok(SourceLocation::Project {
        root,
        files: loaded.files,
    })
}

pub(crate) fn resolve_standalone_file(file_path: &Path) -> Result<PathBuf> {
    let display = file_path.display().to_string();
    let canonical =
        std::fs::canonicalize(file_path).with_context(|| format!("file not found: {display}"))?;
    if !canonical.is_file() {
        anyhow::bail!("`{}` is not a file.", canonical.display());
    }
    if canonical.extension().and_then(|ext| ext.to_str()) != Some("baml") {
        anyhow::bail!(
            "`{}` is not a BAML source file. Use a `.baml` file with `--file`.",
            canonical.display()
        );
    }
    Ok(canonical)
}

/// Resolve `from` (or cwd when omitted) and load all discovered `.baml` files
/// into a fresh
/// [`ProjectDatabase`]. Returns the database, the canonical project root,
/// and the list of loaded files. Used by the build/execute commands
/// (`run`/`test`/`generate`/`pack`).
///
/// **`baml.toml` is opt-in.** A directory is a BAML project if it has
/// *either* a `baml.toml` *or* a `baml_src/` directory — `baml.toml` is
/// only needed when you actually use one of its features (dependencies,
/// version locks, `[scripts]`, multiple packages). The two cases:
///

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Rename the file to have a `.baml` extension if it truly is BAML source.
2. Point --file at the actual `.baml` source file (e.g. baml_src/main.baml), not generated client code or config.
3. If you meant a whole project/config directory, use --project instead.
4. Check the canonical path printed in the error to identify which file was rejected.

Example fix

// before
baml dev --file ./generated_baml_client.py

// after
baml dev --file ./baml_src/main.baml

#!/usr/bin/env bash
F="$1"
case "$F" in
  *.baml) ;;
  *) echo "--file requires a .baml source file, got: $F"; exit 1 ;;
esac

When it happens

Trigger: Passing a file whose canonical path extension is not `baml` (e.g. .txt, .json, main.py, generated .ts) to --file via load_standalone, resolve_source_location, or load_and_compile_standalone.

Common situations: Passing a generated client file (e.g. baml_client/.../main.py) instead of the source; passing baml.config or a manifest file; files renamed to .bak/.txt; forgetting the .baml extension on a newly created source file.

Understand the failure class

Background: "is not a compatible type" / "cannot merge" errors: when a value's type doesn't match what the library requires — this error's family across 65 libraries.

Related errors

• `{}` is not a file.
• compilation failed: {e:?}
• no `.baml` files found in {}
• could not find packaged playground assets. For local debuggi
• `--file` and `--project` are mutually exclusive; `--file` al

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/51e78e816cf64d5c. Report an issue: GitHub.