Citations APIs
Citation APIs answer two different questions: who cites a paper, and how to format a reference. OpenCitations is free with no key and returns references and citing works for a DOI or PMID as JSON or CSV. Semantic Scholar exposes citation graphs across its paper index. Scholar Sidekick turns DOI, PMID, ISBN and arXiv IDs into formatted citations, with fabrication and retraction checks.
| API | Pricing | Auth | Format | Free tier | Status |
|---|---|---|---|---|---|
OpenCitationsOpen scholarly citation links: references and citing works for a DOI, PMID or OMID, as JSON or CSV. Data & Knowledge › Academic | Free | None | JSON | 10k+/day | Live |
Scholar SidekickResolves DOI, PMID, ISBN and arXiv IDs into formatted citations, exports, and fabrication/retraction checks. Data & Knowledge › Academic | Freemium | None | JSON | <100/day | Live |
Semantic ScholarSearch and retrieve papers, authors and citation graphs across 200M+ scholarly works. Data & Knowledge › Academic | Freemium | API key | JSON | — | Degraded |
OpenCitationsFreeLive
Open scholarly citation links: references and citing works for a DOI, PMID or OMID, as JSON or CSV.
None · JSON
10k+/day
no machine-readable spec
Scholar SidekickFreemiumLive
Resolves DOI, PMID, ISBN and arXiv IDs into formatted citations, exports, and fabrication/retraction checks.
None · JSON
<100/day
OpenAPI spec · llms.txt
Semantic ScholarFreemiumDegraded
Search and retrieve papers, authors and citation graphs across 200M+ scholarly works.
API key · JSON
—
OpenAPI spec
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Choosing a Citations API
Is there a free Citations API?
Yes. OpenCitations is free to use, and Semantic Scholar and Scholar Sidekick have a free tier alongside paid plans.
Which Citations APIs work without an API key?
OpenCitations and Scholar Sidekick need no key or sign-up, so you can try them with a plain request.
Can I call a Citations API from front-end JavaScript?
OpenCitations and Scholar Sidekick allow cross-origin requests and need no key, so they work straight from the browser. For the others, call them from your server so your key stays private.
Can I use Citations APIs in a commercial project?
OpenCitations and Scholar Sidekick permit commercial use.
Which Citations APIs work with AI agents?
Semantic Scholar and Scholar Sidekick publish an OpenAPI spec for generating clients and tools.
Broader: Academic APIs · Data & Knowledge APIs
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