Work Out Token Cost and Latency Before Shipping
Added 2026-11-05
A feature more often dies on the cost curve than on a bug.
I am shipping a feature that calls a model: [feature and call pattern]. Budget cost and latency: 1) show the formula for input and output tokens per call, with unit cost; 2) compute conservative, expected, and worst cases from daily actives, call frequency, retries, and cache hit rate; 3) flag design choices that inflate cost — long context, repeated retries, serial calls; 4) list cost levers and their side effects — caching, truncation, a smaller model, batching; 5) set a latency budget with timeouts and a degraded path; 6) name the three metrics to monitor after launch, with alert thresholds. No vague "optimize the prompt" advice.
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Swap the bracketed parts for your own details before sending.
[feature and call pattern]
How to use
Price the worst-case monthly bill first, then decide whether to build it at all.
Try tweaking it
- Have it restate requirements and constraints before writing code.
- Ask for the smallest change plus a rollback path, not a full-file rewrite.
What you should get
- A minimal, runnable change with copy-ready code
- Impact list: which files and call sites must follow
Common mistakes
- Asking it to touch ten files at once, then losing track of what broke what.
- Pasting only the error, with no code or version, and getting an unfixable answer.
How to check the output
- The change runs, can be rolled back, and touches nothing unrelated.
- Edge cases (empty, oversized, concurrent) are covered or explained.
Where it works
- Good for: having it restate requirements and constraints, then propose the smallest runnable change.
- Watch out: include versions and a minimal reproduction with the error, or the fix may look plausible but not fit.