Learn the controls and knobs

The main controls are schema strictness; required versus optional fields; enums; numeric bounds; nullable fields; additionalProperties; schema version; retry policy; validation errors; and separation between extraction and action. Each should be treated as a hypothesis: “changing X will move metric Y under workload Z.” Change one family of controls at a time, record the version, and compare against a baseline.

Start with controls that bound harm—permissions, limits, split integrity, or validation—before controls that polish average quality. Use a small sweep instead of one lucky setting. A setting that wins on one example can lose on a different length, language, class, tenant, or traffic pattern. Keep defaults explicit in configuration so a provider or library update cannot silently redefine the experiment.

A useful control sheet has five columns: control, current value, predicted benefit, predicted cost, and rollback trigger. Fill it using the tradeoff below rather than intuition alone: Strict schemas simplify downstream code but can make partial answers harder. Large nested schemas consume tokens and reduce model reliability. Retries can repair transient failures but may duplicate side effects unless generation and execution are separate.

An invoice extractor returns {invoice_id, currency, total_cents, due_date, confidence}. The schema requires integer cents and ISO dates; a business rule checks that line-item cents sum to total_cents before any payment workflow sees it.

The worked number is if 970 of 1,000 outputs parse and 930 pass the schema, parse rate = 97% but end-to-end schema-valid rate = 93%; report both. State the unit and denominator whenever you report it. A percentage without a denominator can conceal a tiny sample; a latency without a percentile can conceal slow users; a similarity score without a labeled task can conceal irrelevant neighbors. Compare the observed value with a threshold chosen before seeing the final test result.

Now test the tempting shortcut. Suppose the team optimizes only the most visible metric. The result may look better while the system becomes less trustworthy. The reason is concrete: Strict schemas simplify downstream code but can make partial answers harder. Large nested schemas consume tokens and reduce model reliability. Retries can repair transient failures but may duplicate side effects unless generation and execution are separate. This is why the decision record must include both the intended gain and the tolerated regression. If the tolerated regression is unknown, the change is not ready for a consequential workflow.

• Prefer a measured baseline over a persuasive demo.
• Keep versions, inputs, and thresholds reproducible.
• Separate syntactic success from semantic correctness and authorization.
• Escalate or abstain when evidence falls outside the contract.
• Re-evaluate when data, traffic, models, providers, or user goals change.

These rules turn the topic into an engineering decision rather than a slogan. They also make disagreement productive: another person can challenge the assumptions, rerun the evaluation, and reach a documented conclusion.

Select three plausible values for one control while freezing the others. Run the same representative cases at every value and record task quality, p95 latency, unit cost, and failure count. Do not pick the winner from the average alone: inspect the worst case and important slices. Next, repeat one run to estimate natural variation. If the difference between two settings is smaller than run-to-run variation, the evidence does not support declaring a winner. Save the configuration beside the results so the experiment is reproducible after a model or library upgrade.