For API developers who appreciate open-source ecosystems and require a tool that is free and flexible, Hoppscotch is your best choice. Its capabilities for offline and on-premises deployment make it ideal if you are working in isolated environments. However, if your project requires extensive third-party integrations or advanced features, you should look elsewhere.
On the other hand, if you are developing cloud applications and need a local environment that mimics AWS functionalities, LocalStack is the way to go. It allows you to reduce cloud costs and receive immediate feedback during development, making it a strong option for building and testing. Just be aware that it may not suit your needs if you require a fully managed service or prefer open-source solutions.