GraphQL is a query language for APIs and a runtime for executing those queries by using a type system you define for your data. It was developed by Facebook in 2012 and released publicly in 2015. GraphQL provides a more efficient, powerful, and flexible alternative to REST. Here are some scenarios and reasons when and why you might choose GraphQL over REST: [1] **Efficient Data Loading**: With REST, you often have to make multiple requests to different endpoints to fetch related data. GraphQL allows you to fetch all the data you need in a single request. This reduces the number of network round trips and can significantly improve performance, especially on slow mobile networks. [2] **Over-fetching and Under-fetching**: REST APIs often return more data than you need (over-fetching) or require additional requests to get related data (under-fetching). GraphQL lets you specify exactly what data you need, which can reduce the amount of data transferred over the network and improve the performance of your application. [3] **Rapid Product Iterations**: With REST, any changes to the data requirements often require a new version of the API or additional endpoints. GraphQL's flexible nature allows front-end developers to request new fields and types without requiring changes to the backend. This can speed up product development and iteration. [4] **Strongly Typed Schema**: GraphQL APIs are organized in terms of types and fields, not endpoints. Accessing the full capabilities of your data from a single endpoint and having a strongly typed schema means you can validate queries at build time, and you can use tools to generate documentation and API explorers automatically. [5] **Real-time Data with Subscriptions**: GraphQL supports real-time updates through subscriptions. When data changes on the server, the server pushes the update to the client. This is something that REST does not natively support and would require additional setup, such as WebSockets. [6] **Versioning**: Versioning in REST APIs can lead to a proliferation of endpoints and can be a headache to maintain. GraphQL eliminates the need for versioning by allowing you to add new fields and types without impacting existing queries. [7] **Complex Systems and Microservices**: In a microservices architecture, GraphQL can act as a unified gateway that aggregates data from multiple services. This can simplify the client-side code and reduce the complexity of managing multiple REST endpoints. [8] **Tooling and Ecosystem**: GraphQL has a rich ecosystem of tools and libraries that can help with development, such as Apollo and Relay. These tools can help with state management, caching, and more. However, it's important to note that GraphQL is not always the best choice. REST has its own advantages, such as simplicity, caching benefits, and widespread adoption. The decision to use GraphQL or REST should be based on the specific requirements of your project, the complexity of your data, and the needs of your clients. In some cases, a combination of both might be the most pragmatic approach.