API cookbook

Historical replay — reprice as of a prior moment

Reprice any loan using the ratesheet that was active at a given timestamp. Useful for disputes, audit, and lock-day reconstruction.

RTBy RateStack TeamPublished2026-03-15Reviewed2026-03-15

intermediatecURL

curl -fsS -X POST https://api.ratestack.com/v1/pricing/explain \
  -H "X-API-Key: $KEY" \
  -H "Content-Type: application/json" \
  -H "Idempotency-Key: $(uuidgen)" \
  -d '{
    "borrowers":  [{ "fico": 752 }],
    "loan":       { "loanAmount": 425000, "loanType": "CONFORMING", "amortizationType": "FIXED" },
    "property":   { "attachmentType": "DETACHED", "constructionMethod": "SITE_BUILT", "projectLegalStructureType": "NONE", "projectClassificationIdentifier": "NA", "pudIndicator": false, "financedNumberOfUnits": 1, "propertyEstateType": "FEE_SIMPLE", "occupancy": "PRIMARY", "state": "CA", "appraisedValue": 532000 },
    "transaction":{ "type": "PURCHASE" },
    "execution":  { "lockPeriodDays": 30 },
    "asOf": "2025-09-15T14:32:00Z"
  }'

The engine resolves the ratesheet that was ACTIVE at that timestamp and uses it. Comp / margin layers also resolve as of that timestamp. The response includes the resolved ratesheet version and the as-of timestamp so audit can verify.

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