jq belongs in files, pipes, and CI. Input and output are text you can chain. /dev/json-format on this site is for pasting a snippet, seeing structure, and reading a parse error.
Do not paste secrets into random third-party formatters. This tool computes in the browser; still clear the tab, and do not leave production keys sitting there.
If you already have a script or many files, stay in the CLI. If you need to check brackets or show a colleague a payload, the page is faster.
For tokens open /dev/jwt. Decode is not verify. The toolbox is for reading fields; the CLI is for pipelines.