BoundaryML/baml · error

--manifest-base-url requires a value

Error message

--manifest-base-url requires a value

What it means

The `--manifest-base-url` flag used by `baml toolchain` subcommands consumes the next argument as its value. When the flag is the last argument and nothing follows it, `parse_manifest_base_url` throws this error instead of silently treating the missing URL as an empty string.

Solutions

  1. Append the URL value: `--manifest-base-url https://example.com/manifests/` (trailing slashes are trimmed automatically).
  2. Quote the variable and verify it is non-empty before invoking: `[ -n "$URL" ]`.
  3. Omit the flag entirely if you want the default manifest source.

Example fix

# before
URL=""
baml toolchain install nightly --manifest-base-url $URL

# after
URL="https://mirrors.example.com/baml"
baml toolchain install nightly --manifest-base-url "$URL"
Defensive patterns

Strategy: validation

Validate before calling

URL="${MANIFEST_BASE_URL:-}"
cmd=(baml toolchain install nightly)
if [ -n "$URL" ]; then
  [ "$URL" = "${URL#-}" ] || { echo "bad URL" >&2; exit 1; }
  cmd+=(--manifest-base-url "$URL")
fi
"${cmd[@]}"

Type guard

function hasFlagValue(args: string[], flag: string): boolean {
  const i = args.indexOf(flag);
  return i !== -1 && i + 1 < args.length && args[i + 1].length > 0;
}

Try / catch

try:
    subprocess.run(cmd, check=True)
except subprocess.CalledProcessError as e:
    if "--manifest-base-url requires a value" in e.stderr.decode():
        raise SystemExit("--manifest-base-url was given without a URL")

Prevention

When it happens

Trigger: Running e.g. `baml toolchain install nightly --manifest-base-url` with no value after the flag.

Common situations: Shell scripts where the URL variable is empty or unset (`--manifest-base-url $URL` expanding to nothing), copy-paste dropping the URL, or line-wrapped commands losing the last token.

Understand the failure class

Background: "--flag is required" and "must specify" CLI errors: how missing-required-flag validation works and how to fix it — this error's family across 20 libraries.

Related errors

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/da6e9be76f2ebf73. Report an issue: GitHub.

Appendix: source

Thrown at baml_language/crates/baml/src/main.rs:409

        }
        Some(other) => Err(anyhow!(
            "unknown toolchain command {other:?}\n\n{TOOLCHAIN_HELP}"
        )),
    }
}

fn is_help_arg(arg: &str) -> bool {
    matches!(arg, "--help" | "-h" | "help")
}

fn parse_manifest_base_url(mut args: Vec<String>) -> Result<(Vec<String>, Option<String>)> {
    let mut manifest_base_url = None;
    let mut i = 0;
    while i < args.len() {
        if args[i] == "--manifest-base-url" {
            let value = args
                .get(i + 1)
                .ok_or_else(|| anyhow!("--manifest-base-url requires a value"))?
                .trim_end_matches('/')
                .to_string();
            args.drain(i..=i + 1);
            manifest_base_url = Some(value);
        } else {
            i += 1;
        }
    }
    Ok((args, manifest_base_url))
}

fn pass_through(args: Vec<String>) -> Result<i32> {
    let selector = active_selector()?;
    if let Some(cli) = path_selector(&selector.selector) {
        return exec_path_toolchain(cli, &selector, args);
    }
    let version = concrete_version_for_selector(&selector)?;
    let cli = toolchain_cli_path(&version);

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