GeoJSON.io was developed by Mapbox and is "a quick, simple tool for creating, viewing, and sharing spatial data."
It is a perfect way to visualize, test or learn how GeoJSON data is created, formatted, styled or inspected.
We have made updates to GeoJSON.io with Mapbox styles from the Public Domain.
Say you want to visualize this GeoJSON from Joshua Tree. You can open a version of GeoJSON.io with Public Domain Styles.
Once you have opened the app, then paste your GeoJSON URL by tapping Meta, New Window. This will open a new browser tab with your GeoJSON data.
Then you can use the usual tools such as inspecting geometries or view GeoJSON properties in a table.