Hi,

I apologize for the confusion, we need to add better documentation to the jsreportonline.

Is it possible to test the jsreport REST api from a free account's instance?

Absolutely, there is no limitation regarding API calls.

If I try to curl this instance directly it redirects me to the sign in page.

This is probably because you are missing the authorization header.
https://jsreport.net/learn/api#authentication
It should look like this, it is common basic auth standard
Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
Where the hash is based on username and password:
base64(username:password)

With such a header, you can call for example
GET https://xxx.jsreportonline.net/odata/templates

When you want to render something, find details in the API docs
https://jsreport.net/learn/api

Is jsreport intended solely to be self-hosted from a node process? Or can it be accessed from an instance hosted by jsreport?

I am afraid I don't understand what you mean. Can you elaborate?

Jan