Version 1

Small API. Exact contract.

Send the API key in the Authorization header. Dates must be ISO YYYY-MM-DD. Supported range is 2000-01-01 through 2100-12-31.

Single date

curl -X POST https://YOUR-ORIGIN/api/v1/date \
  -H 'Authorization: Bearer fg_live_…' \
  -H 'Content-Type: application/json' \
  --data '{"date":"2026-08-11","config":{"pattern":"454","anchor_rule":"saturday_nearest_jan31","week53_mode":"clamp"}}'

Date range

POST /api/v1/range
{"start":"2026-08-01","end":"2026-08-31","format":"json","config":{"pattern":"454"}}

Ranges are capped at 400 dates. Set format to csv for a downloadable table.

Error contract

{"ok":false,"error":{"code":"INVALID_DATE"}}

Invalid input is 400; missing or invalid authentication is 401; inactive access is 403; quota exhaustion is 429; inactive commercial configuration is 503.

Calendar basis

The default follows the retail convention in which a fiscal year starts on the Sunday after the Saturday nearest January 31. Alternative patterns and the last-Saturday-in-January rule are explicit inputs. Validate the selected rule against your organization’s accounting policy.