restclient.el is described as 'This is a tool to manually explore and test HTTP REST webservices. Runs queries from a plain-text query sheet, displays results as a pretty-printed XML, JSON and even images' and is a HTTP Client in the development category. There are more than 50 alternatives to restclient.el for a variety of platforms, including Mac, Windows, Linux, Web-based and Flathub apps. The best restclient.el alternative is cURL, which is both free and Open Source. Other great apps like restclient.el are Postman, Insomnia REST Client, Yaak and Hoppscotch.
Upcoming API testing tool in beta, built in GoLang, supporting HTTP/gRPC, workspaces, environments, request management, and various content types. Features include dark mode, local data storage, Postman import, environment variable setting, and request chaining.
Treblle is a federated API Intelligence platform delivering full API visibility, security, and control from one integration point.
Croatia
EU
ArdorQuery is a cross-platform tool for performing any HTTP(S) endpoints like REST API, HTML, Images, GraphQL, OData etc.
gRPC is a modern open source high performance Remote Procedure Call (RPC) framework that can run in any environment. It can efficiently connect services in and across data centers with pluggable support for load balancing, tracing, health checking and authentication.
United States
Thunder Client is a hand-crafted lightweight Http Client extension for Visual Studio Code. No separate download needed, Just install the extension from VS Code marketplace.
Milkman is a JavaFx-based workbench for crafting requests / responses. It is not limited to e.g. http (or more specifically rest) requests but can be extended in any imaginable way. It is optimized for fast startup and efficient workflow.
United States
Kreya is a GUI client for gRPC, REST and WebSocket APIs with innovative features for environments, authorizations and more.
Switzerland
API Tester is the first mobile app to test any type of API on the go. Test REST, GraphQL, WebSocket, SOAP, JSON RPC, XML, HTTP, and HTTPS APIs completely for free, on iOS or Android.
Used httpyac CLI tool underneath, which helps you execute _.http and _.rest files. This can be used to quickly execute a single *.http file, but also to execute all files in a folder. httpyac supports HTTP, Rest, GraphQL, WebSocket und gRPC...
