Sure, Insomnia is awesome.

But have you considered these open source alternatives?

They are free, self-hostable and community-driven.

Check by yourself: Hoppscotch , Sparrow .

So is Hoppscotch

Postman-like API client
★ 80.1K API Testing License: MIT
Hoppscotch is a lightweight, web-based API development suite.

Read more about Hoppscotch
So is Sparrow

Next-gen API testing
★ 2.6K API Testing License: AGPL-3.0
Sparrow is your next go-to API development buddy which can help you test, debug, and distribute better APIs while collaborating with your colleagues and making you a better programmer.

Read more about Sparrow