You'll need your page and workspace IDs to connect to pages in your workspace from an external tool. Both can be found in the URL of a page, which take the form:
https://app.calctree.com/edit/workspaceID/pageID
Page ID
As well as in the page URL, you can find your pageID on the RHS integrations pane of your page.
Workspace ID
Your workspaceID can be found in the URL of the page you're in, in a given workspace.
For example, for this URL:
The workspaceID would be ae3d7998-a4c7-41c1-abfd-fb3f07a80f21.
Queries and Mutations
The API allows for two different types of calls, queries and mutations.
Queries
Query API calls let you inspect elements in CalcTree, mainly data and calculations (pages). See this page for details and examples of available queries.