Postman has long been, and continues to be, an industry standard for API testing. Numerous beginner courses for QA engineers dedicate sections to explaining how to use it. Software developers, product owners, database administrators, and many others often have Postman installed as well. Another prominent tool is Insomnia.
Both, unfortunately, push their users to create accounts and share often commercial information with their cloud services. I don't mind online collaboration, it can be really helpful, especially in large teams. However, I dislike when perfectly capable products start introducing artificial barriers that persuade customers to use features they don't need and never asked for. Do I need a cloud workspace to work on a course project? No. There's a term for that: enshittification.

A few months ago, I discovered another API client called Bruno, which offers a healthy alternative.