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The App Definition is validated against a JSON Schema. A document that does not validate is never built and never deployed. That last row is the important one. The schema is not a file you fetch, keep in sync, or point a tool at. It ships inside the CLI, which is why the CLI can answer every question about it.

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Ask the CLI

Answers come from the schema compiled into your build, so they cannot drift from what your CLI will accept. Each answer covers one construct: block_calendar is about 5 KB against the schema’s 212 KB, so asking one question costs a fraction of the document. References are named rather than inlined. That keeps an answer small and points you at the next question instead of flattening the whole tree into one wall of output.

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Do not read the schema

This is the point of the page, and it applies to people and agents alike.
If you are opening a schema file, or scraping the binary, to work out what to write, stop and run cordango vocabulary instead.
That warning is not hypothetical. An agent working in a real workspace went looking for the settings a calendar view accepts, found no way to ask, and extracted the embedded JSON Schema by scraping strings out of the 78 MB executable. It got the right answer by the most fragile route available, and it was about to pull the whole schema in next. The agent was not misbehaving. It filled a hole. cordango vocabulary is that hole filled. If cordango vocabulary cannot answer a question about what may be written, that is a gap worth reporting rather than working around.

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Where one idea has two names

An operation is what you send. A file is what gets written. They diverged for defensible reasons at each step, and the sum is a seam. These are the pairs: cordango vocabulary prints this list too. Every one of these was found by somebody through trial and error before it was written down.

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Validating

You do not run a validator. Two commands already do it. On your source, which is what you almost always want:
Errors point at the file and line you wrote, rather than at a JSON pointer into a generated document. No model, no database, no network. On an existing App Definition, when you have one from somewhere else:
import puts the document through the same schema gate before it writes anything. A document that does not validate does not become source files.

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Versions

Three numbers: the CLI version, the source format version, and the App Definition schema version. schemaVersion in a definition names the third. They move independently.

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Maintaining the schema itself

Only relevant if you are working on Cordango rather than with it. The schema is authored as per-concern source files under schemas/src/ (domain, ui, behavior, notifications, security, and a root holding the envelope and shared primitives) and composed into the single stored contract, with a CI guard that fails if the two drift apart. That is a detail of the repository, not something the CLI asks of you.