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Insomnia REST - Design, debug, test, and mock APIs locally, on Git, or cloud. Build better APIs collaboratively for the most popular protocols with a dev‑friendly UI, built-in automation, and an extensible plugin ecosystem.

JSONFormatter.org - Online JSON Formatter and JSON Validator will format JSON data, and helps to validate, convert JSON to XML, JSON to CSV. Save and Share JSON

Appbase.io - Search stack for building modern apps

JSON Editor Online - View, edit and format JSON online