Contract testing is a fast and lightweight form of API testing that checks the content and format of API requests and responses. It's designed to monitor the API conversation between the consumer and producer, ensuring both sides respect the contract, which is a formal description of the rules governing the interaction. This approach helps teams accelerate API-first development while reducing costs by minimizing false-negatives, rollbacks, test bottlenecks, errors in production, and more. By automating contract test writing and maintenance, contract testing provides instant feedback during early stages of design and development, allowing developers to gain confidence in sending releases to production and quickly diagnose and repair issues. It's particularly beneficial for microservices programs with exponentially increased test cases, enabling teams to scale contract testing without disrupting workflows and providing isolation of the consumer side to reduce the scope of an issue.