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
- 77 ms
- Server probes · 24h
- Subscribers
- 3,999
- active
- Total calls
- 76
- 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
Related APIs
Other APIs with overlapping tags.
Number Words 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
Currency Converter API
Live foreign-exchange conversion across 160+ world currencies — the plain, developer-friendly converter. Get the latest rates for any base currency, convert an amount between any two currencies, read the rate (and inverse) for a single pair, or list every supported currency. Rates are read live from an open exchange-rate source that aggregates a broad set of feeds and covers far more currencies than ECB-only data — including emerging-market and exotic currencies such as the Nigerian naira, Indian rupee or Vietnamese dong. This is the everyday convert / latest-rates utility a checkout, invoice, pricing page or travel app needs — distinct from the FX analytics APIs in the catalogue (historical date ranges, pip and position-size calculators, triangular-arbitrage path maths, currency indices), which compute on rates rather than simply converting them.
api.oanor.com/currencyconverter-api
Crypto Price & Converter API
Live crypto price and currency conversion, served from the public CoinGecko feed with no key and nothing cached. This is a conversion utility, distinct from market-overview, arbitrage and coin-profile tools: it tells you what a coin is worth right now and converts an amount between coins and fiats. The price endpoint returns the live price of one or more coins in one or more currencies at once, each with its market cap, 24-hour volume and 24-hour change — pull Bitcoin and Ethereum in USD, EUR and BTC in a single call. The convert endpoint converts an amount of a coin into a fiat currency or into another coin: two Bitcoin to euros, or one and a half Bitcoin to Ether, with the rate and the result. Coin-to-coin conversions are crossed through USD automatically. The supported endpoint lists every currency you can quote or convert into — dozens of fiats plus the major coins. Everything is read live from CoinGecko on each request, nothing stored beyond a short protective cache. Ideal for wallets, checkout and payment flows, portfolio trackers, price tickers and dashboards. Coin ids are lowercase CoinGecko ids (bitcoin, ethereum, solana). Live, no key. 3 endpoints. For prices by on-chain contract address use a token-price API.
api.oanor.com/cryptoconvert-api
HTML to Markdown API
Convert HTML into clean GitHub-Flavored Markdown. Pass an HTML string, or a live page URL to fetch and convert, and get back tidy Markdown — headings, bold/italic, links, images, lists, blockquotes, code blocks, plus GFM tables, strikethrough and task lists. Script, style and head elements are stripped automatically. Tune the output: ATX or setext headings, the bullet marker, fenced or indented code blocks, inline or referenced links, and the emphasis/strong delimiters; toggle GFM on or off. The inverse of a Markdown-to-HTML renderer. Pure local conversion (the optional URL fetch aside) — no key, no third-party service, instant. Live. 3 endpoints. Built for content migration, web clipping and "save as Markdown", scraping cleanup, CMS import and documentation pipelines.
api.oanor.com/htmltomarkdown-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
Sign in to rate.
No reviews yet.
Discussion
Ask questions, share usage tips, get answers from the provider and other developers. Public — anyone can read.
Sign in to start a thread or reply.
Sign inNew thread
📌 Pinned
🔒 Locked
·
·
·
-
Provider answer
🔒 This thread is locked — no new replies.
-
·
- No threads yet — start the discussion.
Support
Private 1:1 support with the provider — billing questions, integration issues, account problems. Only you and the provider team can see these threads.
Sign in to open a support ticket.
Sign inOpen new ticket
Describe what you need help with. The provider team gets an email and replies on the ticket page.
-
·
Urgent - No tickets yet for this API.