parcel-bundler/parcel · error · ThrowableDiagnostic

Could not determine version of ${pluginName} in ${path.relat

Error message

Could not determine version of ${pluginName} in ${path.relative(process.cwd(), resolveFrom)}. Either include it in "dependencies" or "parcelDependencies".

What it means

When Parcel auto-installs a plugin referenced by a config package, it needs a version range. It looks up the plugin name in the config package's `dependencies` and `parcelDependencies` (and `optionalParcelDependencies`). If none of these provide a range and the plugin isn't optional, Parcel cannot decide which version to install and reports the config file as the source.

Source

Thrown at packages/core/core/src/loadParcelPlugin.js:92

      options.projectRoot,
    );
    if (
      configPkg != null &&
      configPkg.config.dependencies?.[pluginName] == null
    ) {
      // If not in the config's dependencies, the plugin will be auto installed with
      // the version declared in "parcelDependencies".
      range = configPkg.config.parcelDependencies?.[pluginName];
      isOptional =
        Array.isArray(configPkg.config.optionalParcelDependencies) &&
        configPkg.config.optionalParcelDependencies.includes(pluginName);

      if (range == null && !isOptional) {
        let contents = await options.inputFS.readFile(
          configPkg.files[0].filePath,
          'utf8',
        );
        throw new ThrowableDiagnostic({
          diagnostic: {
            message: md`Could not determine version of ${pluginName} in ${path.relative(
              process.cwd(),
              resolveFrom,
            )}. Either include it in "dependencies" or "parcelDependencies".`,
            origin: '@parcel/core',
            codeFrames:
              configPkg.config.dependencies ||
              configPkg.config.parcelDependencies
                ? [
                    {
                      filePath: configPkg.files[0].filePath,
                      language: 'json5',
                      code: contents,
                      codeHighlights: generateJSONCodeHighlights(contents, [
                        {
                          key: configPkg.config.parcelDependencies
                            ? '/parcelDependencies'

View on GitHub (pinned to 59484858a1)

Solutions

Add the plugin to `parcelDependencies` (recommended for config packages) with a semver range.
Or add it to `dependencies` so it ships with the config package.
Re-run the build after editing package.json so the version is resolved.

Example fix

// before (config package package.json)
{ "dependencies": {} }

// after
{ "parcelDependencies": { "@parcel/transformer-image": "^2.0.0" } }

Defensive patterns

Strategy: validation

Validate before calling

// Validate that every plugin referenced by the config is declared.
const declared = new Set([
  ...Object.keys(pkg.dependencies ?? {}),
  ...Object.keys(pkg.parcelDependencies ?? {}),
]);
for (const p of referencedPlugins) {
  if (!declared.has(p)) throw new Error(`declare ${p} in parcelDependencies`);
}

Type guard

function isDeclaredPlugin(name: string, pkg: any): boolean {
  return Boolean(
    pkg.dependencies?.[name] ?? pkg.parcelDependencies?.[name],
  );
}

Prevention

Add every plugin to parcelDependencies when authoring a config package.
Run a config-lint step in CI that cross-checks .parcelrc vs package.json.

When it happens

Trigger: A config package references a plugin by name but its `package.json` omits that plugin from both `dependencies` and `parcelDependencies`.

Common situations: Authoring a config package and forgetting to declare the plugin dependency; adding a pipeline entry without updating package.json.

Related errors

AI-assisted analysis of parcel-bundler/parcel@59484858a1 (2026-08-13). Data as JSON: /api/errors/ac312f6bb2acbfae. Report an issue: GitHub.