windmill-labs/windmill · error

Unknown language '${language}'. Valid languages: ${validLang

Error message

Unknown language '${language}'. Valid languages: ${validLanguages}

What it means

`wmill script bootstrap` resolves the requested language through `languageAliases`, then looks up starter code in `scriptBootstrapCode`. If no bootstrap template exists for the (resolved) language, it throws with the sorted list of valid languages.

Source

Thrown at cli/src/commands/script/script.ts:1634

const languageAliases: Record<string, ScriptLanguage> = {
  python: "python3",
};

async function bootstrap(
  opts: GlobalOptions & { summary: string; description: string },
  scriptPath: string,
  language: ScriptLanguage | string
) {
  if (!validatePath(scriptPath)) {
    return;
  }

  const resolvedLanguage = (languageAliases[language] ?? language) as ScriptLanguage;

  const scriptInitialCode = scriptBootstrapCode[resolvedLanguage];
  if (scriptInitialCode === undefined) {
    const validLanguages = Object.keys(scriptBootstrapCode).sort().join(", ");
    throw new Error(
      `Unknown language '${language}'. Valid languages: ${validLanguages}`
    );
  }

  const config = await readConfigFile();

  const extension = filePathExtensionFromContentType(
    resolvedLanguage,
    config.defaultTs
  );
  const scriptCodeFileFullPath = scriptPath + extension;
  const scriptMetadataFileFullPath = scriptPath + ".script.yaml";

  try {
    await stat(scriptCodeFileFullPath);
    throw new Error("File already exists: " + scriptCodeFileFullPath);
  } catch (e: any) {
    if (e.message?.startsWith("File already exists")) throw e;

View on GitHub (pinned to e474e8803c)

Solutions

1. Use one of the languages listed in the error message.
2. Check for a language alias (e.g. `deno` for typescript-deno) supported by your CLI version.
3. Update the CLI (`npm i -g windmill-cli` or `brew upgrade wmill`) if the language is newer than your installed version.
4. Run `wmill script bootstrap --help` to see accepted values.

Example fix

// before
wmill script bootstrap f/my_script js
// after
wmill script bootstrap f/my_script typescript

const valid = ['python','typescript','go','shell','bun','deno','ansible','bash','powershell','php','rust','sql','nunjucks','graphql'];
if (!valid.includes(lang)) {
  throw new Error(`Language '${lang}' not supported; use one of: ${valid.join(', ')}`);
}

function isSupportedLanguage(l: string): l is SupportedLanguage {
  return ['python','typescript','go','shell','bun','deno'].includes(l);
}

try {
  await wmill.script.bootstrap(path, lang);
} catch (e) {
  if (String(e.message).startsWith('Unknown language')) {
    console.error(e.message); // message lists valid languages
  }
  throw e;
}

When it happens

Trigger: `wmill script bootstrap my_script <lang>` with a misspelled or unsupported language value, e.g. `python3` when only `python` is aliased, `js` instead of `typescript`, or `bash` instead of `shell`/`bun`.

Common situations: Typing a language name from another tool's vocabulary (`golang` vs `go`, `py` vs `python`); copying a command from docs for a Windmill version that doesn't support that language yet; shell tab-completion inserting the file extension (`.ts`) instead of the language name.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• Invalid migration name '${name}': use only letters, digits,
• Unknown workspace dependencies file format: ${path}. Valid f
• Cannot push flow ${remotePath}: step(s) reference non-worksp
• Completed jobs file must contain an array of jobs
• Queued jobs file must contain an array of jobs

AI-assisted analysis of windmill-labs/windmill@e474e8803c (2026-09-03). Data as JSON: /api/errors/f6b1fdc1b139c7dc. Report an issue: GitHub.