This paper highlights the need for a standardized registry system for autonomous AI agents scaling in cloud, enterprise, and distributed environments. It examines three leading registry approaches: MCP's mcp.json, A2A's Agent Card, and NANDA's AgentFacts. Each approach utilizes a unique metadata model, featuring a centralized metaregistry (MCP), decentralized interaction (A2A), and a cryptographically verifiable and privacy-preserving metadata model (NANDA). The paper compares and analyzes the three approaches across four dimensions: security, scalability, authentication, and maintainability, and offers suggestions and recommendations for the future design and adoption of registry systems for the Internet of AI agents.