What causes "ACP source.packageJson must not be empty." in vercel/ai?

Populate source.packageJson with the actual package.json file contents before calling createACPV1.

ACP source.packageJson must not be empty.

Error message

ACP source.packageJson must not be empty.

What it means

validateACPV1Implementation checks an ACPImplementation of type 'npm-locked' for required source artifacts. It throws when source.packageJson is an empty string, since launching the agent from a locked npm workspace requires package.json contents.

Source

Thrown at packages/harness-acp/src/v1/implementation.ts:60

    credentialEnv: settings.credentialEnv,
    env: settings.env,
  };
}

const EXACT_SEMVER_REGEXP =
  /^(0|[1-9]\d*)\.(0|[1-9]\d*)\.(0|[1-9]\d*)(?:-[0-9A-Za-z-]+(?:\.[0-9A-Za-z-]+)*)?(?:\+[0-9A-Za-z-]+(?:\.[0-9A-Za-z-]+)*)?$/;
const PACKAGE_NAME_REGEXP =
  /^(?:@[a-z0-9][a-z0-9._-]*\/)?[a-z0-9][a-z0-9._-]*$/;
const EXECUTABLE_NAME_REGEXP = /^[A-Za-z0-9][A-Za-z0-9._-]*$/;
const ENVIRONMENT_VARIABLE_NAME_REGEXP = /^[A-Za-z_][A-Za-z0-9_]*$/;

export function validateACPV1Implementation(
  implementation: ACPImplementation,
): void {
  const { source } = implementation;
  if (source.type === 'npm-locked') {
    if (source.packageJson.length === 0) {
      throw new Error('ACP source.packageJson must not be empty.');
    }
    if (source.pnpmLockYaml.length === 0) {
      throw new Error('ACP source.pnpmLockYaml must not be empty.');
    }
    if (source.pnpmWorkspaceYaml?.length === 0) {
      throw new Error('ACP source.pnpmWorkspaceYaml must not be empty.');
    }
  } else if (source.type === 'npm-simple') {
    validateNpmSimpleSource({ source });
  } else if (source.command.trim().length === 0) {
    throw new Error('ACP source.command must not be empty.');
  }
  if (!EXECUTABLE_NAME_REGEXP.test(implementation.executable)) {
    throw new Error(
      `ACP executable must be a bare command name without a path; received ${JSON.stringify(implementation.executable)}.`,
    );
  }

View on GitHub (pinned to 69428b1f8b)

Solutions

Populate source.packageJson with the actual package.json file contents before calling createACPV1.
Fix the file-read step so failures surface instead of silently yielding an empty string.
If no lockfile workspace is needed, use a different source.type (e.g. 'npm-simple') with its required fields.

Example fix

// before
createACPV1({ implementation: { source: { type: 'npm-locked', packageJson: '', pnpmLockYaml: lock } } });
// after
const packageJson = await fs.readFile('package.json', 'utf8');
createACPV1({ implementation: { source: { type: 'npm-locked', packageJson, pnpmLockYaml: lock } } });

Defensive patterns

Strategy: validation

Validate before calling

if (source.type === 'npm-locked' && source.packageJson.length === 0) {
  throw new Error('source.packageJson is empty; load package.json contents before createACPV1');
}

Try / catch

try {
  createACPV1({ implementation });
} catch (error) {
  if (error instanceof Error && error.message.includes('packageJson must not be empty')) {
    throw new Error('Implementation packaging failed: package.json was not embedded');
  }
  throw error;
}

Prevention

Read package.json with error-throwing file APIs (never default to '').
Assert all npm-locked source fields are non-empty in CI before launching.
Bundle required artifacts (package.json, pnpm-lock.yaml) in your packaging step and verify their sizes.

When it happens

Trigger: Calling createACPV1 with a 'npm-locked' source whose packageJson field is '' (empty string), typically from an unread/failed file load or a placeholder config.

Common situations: Build/packaging step that omitted package.json; reading the file with a helper that returned '' on error; hand-written config with an empty placeholder.

Related errors

AI-assisted analysis of vercel/ai@69428b1f8b (2026-08-30). Data as JSON: /api/errors/5f7ff02be180b599. Report an issue: GitHub.