Modern applications are largely API-driven. API testing should cover functional validation as well as performance, security, and contract compliance.
Postman: Easy UI, collections, and automation for API testing. CI/CD integration and Newman for command-line runs.
REST Assured (Java): Code-based, BDD-style syntax, and framework integration (JUnit, TestNG) for a developer-friendly option.
Contract testing (Pact, Spring Cloud Contract): Verifies the API contract between consumer and provider; valuable in microservices to catch mismatches early.
Strategy: Start with core functional and contract tests, then add load and security tests as needed.