Agent Plugins 1.0.0 ships a JSON Schema for plugin.json . It sets additionalProperties: false . So the obvious loader is four lines: const manifest = JSON . parse ( await readFile ( join ( dir , ' plugin.json ' ))); if ( ! validate ( manifest )) return reject ( ' invalid manifest ' ); That loader is wrong, and the specification says so in a sentence most people never reach. §5.2: Clients MUST report and ignore each unknown fi...