API security encompasses the strategies and measures designed to protect Application Programming Interfaces (APIs) from threats, vulnerabilities, and attacks, as APIs are crucial for software systems' communication and often involve sensitive data exchange. Unlike traditional web security, which relies on a "castle and moat" model, API security faces unique challenges due to the complexity and rapid evolution of modern applications, necessitating constant updates to security tools. Essential API security practices include penetration testing, fuzz testing, authentication and authorization testing, and input validation to address vulnerabilities like SQL injection and cross-site scripting. Various tools such as OWASP ZAP, Postman, and Burp Suite assist in testing and securing APIs, while standards like OAuth 2.0, TLS, and OWASP API Security Top 10 provide frameworks for consistent security implementations. Shadow APIs, often ungoverned and undocumented, pose significant security risks as they can bypass key enforcement layers, highlighting the need for comprehensive API lifecycle governance and observability. Effective API security requires a combination of robust testing methods, adherence to established security standards, and proactive management of shadow APIs to prevent potential breaches and ensure data protection.