Stoplight Studio is a powerful GUI/text editor with linting and mocking built right in. The desktop version has been discontinued, but it runs in the browser, powered by your existing GitHub, GitLab, or BitBucket repos.
This is a REPL OpenAPI3 description document text editor. It provides both a CLI and and a REPL you can use to test your APIs, but you can also test database queries, start and stop database (containers), generate fake data automatically, start your test microservice and much more. You don't have to exit from your REPL! Or you can use the CLI to do the same if you want, giving you the option to automatize your contract-first based dev cycles.