Insomnia API Client alternatives include RapidAPI Client, Postman, Hoppscotch, Advanced Rest Client (ARC), APIRequest.io, RESTer, Reqbin, and REST ninja. Each has its own installation type and user interface, performance characteristics, documentation quality, and pricing models. For example, RapidAPI Client is an online alternative with a simple pricing model, while Postman is a complex application with a steep learning curve and various add-ons. Hoppscotch is a fast and free online API client, while ARC is a Chrome extension with a detailed but overwhelming feature list. APIRequest.io and RESTer are also free online tools, whereas Reqbin offers a premium product for API debugging. REST ninja is a simple and free online tool without any advertisements or premium products. The best API Client depends on individual needs and preferences, as each alternative has its strengths and weaknesses.