Prove the batch fits before you start it

Some free tiers have a strange, exploitable shape: a painfully low rate ceiling paired with a huge monthly token budget (Mistral's free Experiment tier, as of 2026-06: about 2 requests/minute but around a billion tokens/month). Useless for anything live; ideal for a patient overnight grind. The failure mode is starting the job unsized and finding it stalled, or 12% done, in the morning. Your job is the arithmetic, up front.

Steps

1. Count the backlog: how many items, and a realistic esttokensper_item (input + output; when unsure, run 3 samples and measure rather than guessing).
2. Look up the tier's actual limits (the rate ceiling in requests/minute and any monthly token budget) from the provider's current docs, not from memory or this file.
3. Compute two numbers and show both:

- Budget fit: items x tokens/item vs. the monthly budget. Over budget means shrink the job or split it across months. - ETA: items / (rpm x 60) hours at the ceiling. This tells the user whether "overnight" is 8 hours or 3 days; both are fine, but only if known in advance.

1. Run the proof below; it fails on a job that doesn't fit its budget.
2. Only then queue it, with a runner that actually paces to the rate limit (bursting past it gets throttled or banned, which destroys the ETA you just computed).

Prove it

```bash verify cat > batch.json <<'JSON' { "provider": "mistral", "items": 3000, "ratelimitrpm": 2, "esttokensperitem": 1200, "monthlytokenbudget": 1000000000 } JSON node -e ' const c = JSON.parse(require("fs").readFileSync("batch.json", "utf8")); function bad(m) { console.error("BAD: " + m); process.exit(1); } if (!c.items || c.items < 1) bad("no items to process"); if (!c.ratelimitrpm || c.ratelimitrpm < 1) bad("ratelimitrpm must be at least 1"); if (!c.esttokensperitem || c.esttokensperitem < 1) bad("esttokensperitem must be set (measure 3 samples if unsure)"); const used = c.items c.esttokensperitem; if (c.monthlytokenbudget && used > c.monthlytokenbudget) bad("job needs " + used + " tokens but the monthly budget is " + c.monthlytokenbudget); const etaH = (c.items / (c.ratelimitrpm 60)).toFixed(1); console.log("batch OK: " + c.items + " item(s) at " + c.ratelimitrpm + " req/min = ~" + etaH + "h, using " + used + " of " + c.monthlytoken_budget + " monthly tokens"); '

## Guardrails

- Nothing live or interactive belongs on a 2-requests/minute tier. This pattern is for a one-time backlog with nobody waiting on it.
- Free tiers often use prompts to improve models. Sensitive or confidential material goes on a paid tier; still pennies, and worth it.
- This pays off for a single big grind, not recurring work. If the same batch runs weekly, price a paid lane and compare honestly.

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<sub>Backed by a machine-verified recipe, re-checked by CI: [Grind a huge one-time job overnight on a free tier](https://flowstacks.xyz/workflows/free-tier-overnight-batch)</sub>