#roman-numerals

Roman numeral conversion as an API, computed locally and deterministically. The encode endpoint turns an integer from 1 to 3999 into its Roman numeral using standard subtractive notation, so 1994 becomes MCMXCIV and 2024 becomes MMXXIV. The decode endpoint turns a Roman numeral back into an integer with strict validation — it rejects malformed forms such as IIII or VV and also returns the canonical way to write the same value, accepting any letter case. The arithmetic endpoint adds, subtracts or multiplies two values given as either integers or Roman numerals and returns the result as a Roman numeral and as an integer, provided the result stays within the classic 1–3999 range. The standard subtractive pairs are IV, IX, XL, XC, CD and CM. Everything is computed locally and deterministically, so it is instant and private. Ideal for typesetting, publishing, education, clock-face, game and document-processing app developers, numbering and chapter tools, and history teaching. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is Roman numeral conversion; for binary, octal and hexadecimal number-base conversion use a base-conversion API.

api.oanor.com/roman-api

Format numbers in human-readable forms as an API. Spell any number in English words — handling thousands through quintillions, negatives and decimals (e.g. 1,234,567 → "one million two hundred thirty-four thousand five hundred sixty-seven", 12.56 → "twelve point five six"). Turn a whole number into its ordinal, both short (21 → 21st, 113 → 113th) and written out (twenty-first, one hundred thirteenth). And convert any whole number from 1 to 3999 to Roman numerals and back (2024 ⇄ MMXXIV), with strict validation. Everything runs locally, so it is fast and always available. Ideal for invoices, cheques and accounting, legal documents, internationalisation, accessibility (screen readers), education and any UI that turns digits into words.

api.oanor.com/numberwords-api