CoplayDev/unity-mcp · error · ValueError

No version found in package.json

Error message

No version found in package.json

What it means

Raised as ValueError by load_package_version() when MCPForUnity/package.json exists and parses as valid JSON, but either has no "version" key at all or the key's value is falsy (null, empty string). The script cannot proceed without a version to propagate to the other files.

Source

Thrown at tools/update_versions.py:54

REPO_ROOT = Path(__file__).resolve().parents[1]
PACKAGE_JSON = REPO_ROOT / "MCPForUnity" / "package.json"
MANIFEST_JSON = REPO_ROOT / "manifest.json"
PYPROJECT_TOML = REPO_ROOT / "Server" / "pyproject.toml"
SERVER_README = REPO_ROOT / "Server" / "README.md"
ROOT_README = REPO_ROOT / "README.md"
ZH_README = REPO_ROOT / "docs" / "i18n" / "README-zh.md"


def load_package_version() -> str:
    """Load version from package.json."""
    if not PACKAGE_JSON.exists():
        raise FileNotFoundError(f"Package file not found: {PACKAGE_JSON}")

    package_data = json.loads(PACKAGE_JSON.read_text(encoding="utf-8"))
    version = package_data.get("version")

    if not version:
        raise ValueError("No version found in package.json")

    return version


def update_package_json(new_version: str, dry_run: bool = False) -> bool:
    """Update version in MCPForUnity/package.json."""
    if not PACKAGE_JSON.exists():
        print(f"Warning: {PACKAGE_JSON.relative_to(REPO_ROOT)} not found")
        return False

    package_data = json.loads(PACKAGE_JSON.read_text(encoding="utf-8"))
    current_version = package_data.get("version", "unknown")

    if current_version == new_version:
        print(f"✓ {PACKAGE_JSON.relative_to(REPO_ROOT)} already at v{new_version}")
        return False

    print(

View on GitHub (pinned to c21bf496bc)

Solutions

1. Open MCPForUnity/package.json and confirm a top-level "version" key exists with a semver string, e.g. "version": "9.2.0".
2. If the field is missing, add it. If it is null/empty, set it to the current release version.
3. Validate the JSON with python3 -c "import json; print(json.load(open('MCPForUnity/package.json')).get('version'))" to confirm the key resolves.
4. Alternatively, pass --version to update_versions.py to bypass auto-detection entirely.

Example fix

// before — MCPForUnity/package.json
{
  "name": "io.coplay.mcpforunity"
}

// after
{
  "name": "io.coplay.mcpforunity",
  "version": "9.2.0"
}

import json
from pathlib import Path

data = json.loads(Path("MCPForUnity/package.json").read_text())
version = data.get("version")
if not version:
    raise SystemExit("package.json has no 'version' field. Set it before running.")
print(f"Detected version: {version}")

def has_valid_version(package_path: Path) -> bool:
    try:
        data = json.loads(package_path.read_text(encoding="utf-8"))
    except (OSError, json.JSONDecodeError):
        return False
    return bool(data.get("version"))

When it happens

Trigger: package.json was hand-edited and the version field was deleted or commented out (JSON has no comments, but a broken edit can leave it absent); a code generator or merge conflict produced a package.json without the version field; the field exists but is set to null or "".

Common situations: A merge conflict in package.json left the version field unresolved or removed; an automated tool rewrote package.json and dropped the version key; the file is a template or stub that was never populated.

Related errors

• Package file not found: {PACKAGE_JSON}
• Failed to write config file '{path}': {ex.Message}
• The selected uvx executable does not exist
• The selected Claude CLI executable does not exist
• Invalid MCP base URL: {baseUrl}

AI-assisted analysis of CoplayDev/unity-mcp@c21bf496bc (2026-08-13). Data as JSON: /api/errors/22db0bc89b3637fa. Report an issue: GitHub.