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
- 90 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
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
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
TOML API
Convert and validate TOML — the config format behind Cargo.toml, pyproject.toml, Netlify and many tools. Turn TOML into JSON, turn JSON back into clean spec-compliant TOML 1.0, and validate any TOML with a precise error message (line and column) when it is malformed. Tables, arrays of tables, inline tables, typed values and datetimes are all handled. Input via the query string or the request body (up to 4 MB). Pure local processing — no key, no third-party service, instant. Live. 4 endpoints. Completes the oanor config-format family alongside the JSON, YAML, XML and CSV APIs — built for build tooling, config editors, CI and data pipelines.
api.oanor.com/toml-api
XML API
A fast, fully-local XML toolkit: convert XML to JSON and JSON to XML with configurable attribute handling, validate XML well-formedness with line and column error details, and pretty-print XML while preserving element order. Every endpoint accepts input via the query string or the request body, up to 2 MB. Pure server-side compute, no third-party upstream, so responses are instant and always available. Ideal for system integrations, SOAP and legacy interop, RSS and sitemap processing, config tooling and data pipelines.
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
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.