What causes "`{}` is not a file." in BoundaryML/baml?

Pass a path to an actual file, not a directory: `--file baml_src/main.baml`.

`{}` is not a file.

Error message

`{}` is not a file.

What it means

resolve_standalone_file canonicalizes the --file path and verifies it is a regular file. If the path exists (canonicalize succeeded) but is a directory or special file (not `is_file()`), the CLI bails with this message. It catches the common mistake of passing a directory to --file.

Source

Thrown at baml_language/crates/baml_cli/src/project_load.rs:70

    }

    let loaded = match reporter {
        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

View on GitHub (pinned to bd85ce9dee)

Solutions

Pass a path to an actual file, not a directory: `--file baml_src/main.baml`.
If you intended to load a whole directory, use --project instead of --file.
Check the path printed in the error and confirm with `ls -la` that it is a regular file.
Fix broken symlinks pointing at directories.

Example fix

// before
baml dev --file ./baml_src

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

Defensive patterns

Strategy: validation

Validate before calling

#!/usr/bin/env bash
F="$1"
if [ -d "$F" ] || [ ! -f "$F" ]; then echo "--file needs a regular file, got: $F"; exit 1; fi

Prevention

Always pass a concrete .baml file path to --file, never a directory.
Use --project for directories.
Verify with `test -f` in scripts before invoking the CLI.

When it happens

Trigger: Calling --file with a path that canonicalizes successfully but is a directory (e.g. `--file ./baml_src`) or a socket/fifo, from load_standalone, resolve_source_location, or load_and_compile_standalone.

Common situations: Pointing --file at the baml_src directory instead of a file inside it; a trailing-slash directory path; expecting --file to accept project roots like --project does; a broken symlink resolving to a directory.

Related errors

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/9261faeafaee0533. Report an issue: GitHub.