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API · /opencitations-api

OpenCitations API

healthy 4,375 Subscribers

Scholarly citations as open data — powered by OpenCitations (COCI), the open citation index. Unlike a metadata lookup, OpenCitations treats every citation as a first-class object: given a DOI you can list the papers that cite it (incoming citations) and the papers it references (outgoing), each annotated with its OpenCitations Identifier (OCI), the date the citation was created, the timespan between the two works, and whether it is a journal- or author-self-citation. Plus quick citation and reference counts for any DOI. It is built for citation-network and bibliometric work — research-impact analysis, self-citation detection, citation-timespan studies and science mapping — and is distinct from scholarly-metadata services (Crossref, OpenAlex). From a single paper to a whole reference graph, ideal for bibliometrics, research-analytics and reference-management tools. Open data from OpenCitations (CC0).

#citations #bibliometrics #research #scholarly #doi #science
api.oanor.com/opencitations-api
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Machine-readable spec so AI agents can integrate this API.

/api/opencitations-api/openapi.json
/api/opencitations-api/llms.txt

Discovery: GET /api/index.json lists every API.

API health

healthy
Uptime
100.00%
Server probes · 24h
Avg latency
634 ms
Server probes · 24h
Subscribers
4,375
active
Total calls
10
last 7 days
status Full status page → · 14 probes/24h

Pricing

Pick a tier — billed monthly, cancel anytime.

Free

Free

  • 2,800 calls / month
  • 2 requests / second
  • Hard cap (429 above quota, no overage)
  • 2,800 calls/month
  • 2 req/sec
  • Citations + references + counts
  • No credit card
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Starter

€7.60 /month

  • 58,000 calls / month
  • 8 requests / second
  • Hard cap (429 above quota, no overage)
  • 58k calls/month
  • 8 req/sec
  • Timespan + self-citation flags
  • Email support
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Pro

€24.00 /month

  • 270,000 calls / month
  • 20 requests / second
  • Hard cap (429 above quota, no overage)
  • 270k calls/month
  • 20 req/sec
  • Bibliometrics & analytics apps
  • Priority support
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Mega

€63.00 /month

  • 950,000 calls / month
  • 50 requests / second
  • Hard cap (429 above quota, no overage)
  • 950k calls/month
  • 50 req/sec
  • Research-impact platform
  • Dedicated SLA
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Related APIs

Other APIs with overlapping tags.

Europe PMC API

Europe PMC as an API, powered by EMBL-EBI — an open repository of biomedical and life-sciences literature covering 45 million+ abstracts and 9 million+ full-text articles drawn from PubMed, PubMed Central, preprint servers (bioRxiv and medRxiv), patents and Agricola. Search the literature with rich field syntax (by author, title, journal, MeSH term, publication year or open-access status), ordering results by relevance, date or citation count, and optionally restricting to preprints only; read an article's full metadata and abstract — its authors, journal, volume and pages, DOI, PubMed and PMC identifiers, MeSH terms, keywords, funding grants and links to the free full text; and walk the citation network in both directions: the articles that cite a given paper, and the works that paper itself references. Together these let you measure scholarly impact, build citation graphs, track a research topic across preprints and peer-reviewed papers, and feed evidence into bibliometric, systematic-review and research-intelligence tools. Article identifiers are PubMed ids (numeric), PMC ids (PMC…) or preprint ids (PPR…); the source defaults to PubMed (MED). Data from EMBL-EBI Europe PMC.

api.oanor.com/europepmc-api

OpenAlex Scholarly API

Open scholarly analytics as an API, powered by OpenAlex — the open index of the world\x27s research covering over 250 million works and 90 million authors. Look up researcher profiles with their total works, citation counts, h-index, i10-index and current affiliation, fetch any author by OpenAlex id or ORCID, rank institutions (universities and labs) by research output and citations, search hundreds of millions of scholarly works complete with citation counts, open-access status, venue and author lists (sortable by citations or date), and explore the full topic taxonomy of science by domain, field and subfield. Perfect for research-intelligence and bibliometrics tools, university and grant dashboards, literature-discovery apps, science maps and citation analysis. All data is CC0 and live. No accounts, no upstream key. For DOI metadata use the Crossref API and for preprints the arXiv API.

api.oanor.com/openalex-api

Crossref API

Search scholarly literature and look up rich publication metadata from Crossref, the DOI registry behind millions of journal articles, books, chapters, conference papers and datasets. Full-text search across 150+ million works with relevance or citation sorting and optional filters, retrieve any work by its DOI (plain, doi: or URL form accepted), and search journals and publishers. Every work comes back as a clean record with title, authors and ORCIDs, journal/container, publisher, publication date, volume/issue/page, ISSN/ISBN, abstract, subjects, license and citation count. Authoritative open scholarly metadata delivered through a fast, reliable API — ideal for reference managers, repositories, research analytics, discovery tools and academic apps.

api.oanor.com/crossref-api

Research Organizations API

Every research organization in the world as an API — powered by ROR, the Research Organization Registry. ROR assigns a persistent open identifier (a ROR ID) to universities, government labs, companies, nonprofits, hospitals, archives and research facilities, with rich, curated metadata and crosswalks to GRID, ISNI, Wikidata and the Crossref Funder Registry. Search the registry by name (and filter by country or organization type); resolve any ROR ID to its full record — names, acronyms and aliases, types, location (city, country, coordinates), website, domains, external identifiers and relationships to parent and child organizations; and match a messy free-text affiliation string ("Dept. of Physics, Heidelberg University, Germany") to the most likely organizations with a confidence score — perfect for cleaning and disambiguating author-affiliation data. It is a research-organization identifier registry, distinct from a plain university directory, and a natural companion to ORCID (for people) in any scholarly-metadata stack. Open data from ROR (CC0).

api.oanor.com/ror-api

Frequently asked questions

Quick answers about pricing, quotas, and integration.

How do I get an API key for OpenCitations API?
Sign up for free at oanor.com, generate an API key from the developer dashboard, and call OpenCitations API with the x-oanor-key header. No credit card needed for the free tier.
What's the rate limit for OpenCitations 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 OpenCitations API cost?
OpenCitations API has a free tier with 100 calls / month. Paid plans start at €7.60 / 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 OpenCitations API GDPR-compliant?
All requests to OpenCitations 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/opencitations-api/SOME_PATH \
  -H "x-oanor-key: oanor_test_..."
const res = await fetch("https://api.oanor.com/opencitations-api/SOME_PATH", {
  headers: { "x-oanor-key": "oanor_test_..." }
});
const data = await res.json();
$ch = curl_init("https://api.oanor.com/opencitations-api/SOME_PATH");
curl_setopt($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/opencitations-api/SOME_PATH",
    headers={"x-oanor-key": "oanor_test_..."},
)
print(r.json())

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