Roman arithmetic
API · /roman-api
Roman Numeral API
healthy
3,999 Subscribers
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
API health
healthy- Uptime
- 100.00%
- Server probes · 24h
- Avg latency
- 88 ms
- Server probes · 24h
- Subscribers
- 3,999
- active
- Total calls
- 28
- last 7 days
Pricing
Pick a tier — billed monthly, cancel anytime.
Free
Free
- 5,000 calls / month
- 2 requests / second
- Hard cap (429 above quota, no overage)
- 5,000 calls/month
- 2 req/sec
- Encode + decode + arithmetic
- No credit card
Starter
€5.00 /month
- 47,000 calls / month
- 6 requests / second
- Hard cap (429 above quota, no overage)
- 47,000 calls/month
- 6 req/sec
- Strict validation, canonical form
- Email support
Pro
€13.00 /month
- 225,000 calls / month
- 15 requests / second
- Hard cap (429 above quota, no overage)
- 225,000 calls/month
- 15 req/sec
- Publishing & document pipelines
- Priority support
Mega
€41.00 /month
- 1,320,000 calls / month
- 40 requests / second
- Hard cap (429 above quota, no overage)
- 1,320,000 calls/month
- 40 req/sec
- Platform scale
- Dedicated SLA
Built by
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api.oanor.com/xml-api
Frequently asked questions
Quick answers about pricing, quotas, and integration.
How do I get an API key for Roman Numeral API?
Sign up for free at oanor.com, generate an API key from the developer dashboard, and call Roman Numeral API with the x-oanor-key header. No credit card needed for the free tier.
What's the rate limit for Roman Numeral API?
Free tier allows 1 request per second. Paid plans scale up to 50 requests per second on the Mega tier. Hard limits return HTTP 429 above the quota — no surprise overage charges.
How much does Roman Numeral API cost?
Roman Numeral API has a free tier with 100 calls / month. Paid plans start at €5.00 / month with higher quotas and faster rate limits.
Can I cancel my subscription anytime?
Yes. Plans are billed monthly and you can cancel anytime from your billing dashboard. No long-term contracts and no cancellation fee.
Is Roman Numeral API GDPR-compliant?
All requests to Roman Numeral API go through our EU-based gateway. Your upstream API key never leaves our server and no personal data is shared with the upstream provider beyond the request you send.
Pick an endpoint from the list on the left to see its details and try it.
Code snippets
Sign up to get an API key, then call any path under your slug.
curl https://api.oanor.com/roman-api/SOME_PATH \
-H "x-oanor-key: oanor_test_..."const res = await fetch("https://api.oanor.com/roman-api/SOME_PATH", {
headers: { "x-oanor-key": "oanor_test_..." }
});
const data = await res.json();$ch = curl_init("https://api.oanor.com/roman-api/SOME_PATH");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, ["x-oanor-key: oanor_test_..."]);
$response = curl_exec($ch);import requests
r = requests.get(
"https://api.oanor.com/roman-api/SOME_PATH",
headers={"x-oanor-key": "oanor_test_..."},
)
print(r.json())Ratings
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