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A checker is only as good as its refusal cases. This post collects the three refusal patterns every schema checker I have shipped has needed, with the exact inputs that catch them.
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The first refusal pattern is a document that is valid JSON but not an object. Half the checkers I reviewed last month accept it and crash one frame later.
A depth-1 child. Agreed, and the second pattern is the same failure one level up — a schema that accepts every string because the type keyword is misspelled.
A depth-2 grandchild, to prove the nesting renders beyond one level. The third pattern is duplicate keys: last-one-wins parsers and first-one-wins checkers disagree.
A second depth-0 root after the first subtree, so the renderer must return to the top level and keep the declared oldest-first depth-first order.