OpenCitations

OpenCitations is an open science research infrastructure providing free access to scholarly bibliographic and citation data. It offers REST APIs for querying citation networks, DOI-based citation lookups, reference data, and bibliographic metadata from millions of research articles. All data is published under CC0 Public Domain Waiver for unrestricted reuse.

OpenCitations publishes 6 API contracts indexed on the APIs.io network, including Authors API, Citations API, Editors API, and 3 more. Tagged areas include Citations, Scholarly, Research, Open Science, and Bibliometrics.

The OpenCitations catalog on APIs.io includes 1 JSON-LD context and 1 Spectral governance ruleset.

OpenCitations’ developer surface includes authentication and 3 more developer resources.

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26.5/100 thin ▬ flat Agent 27/100 agent aware Front door AI 1/6 silent Heartbeat 74/100 slowing Full breakdown ↓
scored 2026-11-13 · rubric v0.28.0 · Show this score on your site →

2 published contracts

Citations Scholarly Research Open Science Bibliometrics DOI Academic

Kin Score

Kin Score How this is scored →
scored 2026-11-13 · rubric v0.28.0

Composite quality — 26.5/100 · thin

Contract Quality 12.3 / 21

Developer Ergonomics 3.6 / 17

Access Clarity 0.0 / 17

Operational Transparency 0.0 / 11

Contract Governance 1.4 / 10

Discoverability 6.2 / 9

Regulatory Posture 1.6 / 15

Agent readiness — 27/100 · agent aware

Machine-Readable Contract 18 / 18

Agentic Access Contract 10 / 10

Documented Reversibility 6 / 6

MCP Server 0 / 12

Machine-Readable Auth 10 / 10

Idempotency 9 / 9

Stable Error Semantics 0 / 8

Request/Response Examples 7 / 7

Rate-Limit Signaling 7 / 7

Typed Event Surface 0 / 6

Agent Skills 0 / 5

Well-Known Catalog 0 / 4

Consent & Bot Identity 0 / 3

A2A Agent Card 0 / 8

Dry-Run / Simulate Mode 4 / 4

Delegated User Identity 0 / 6

Protected Resource Metadata 0 / 5

Registration Without a Human 0 / 6

Agentic Commerce Well-Known Document 0 / 5

Pagination 0 / 5

Distinct Operations 3 / 3

MCP Tool Quality 6 / 6

Regulatory Posture applies to this provider. Its tags matched the Education & Research regime, so Regulatory Posture carries 15 points of the composite. If this regime is wrong for your business, say so on your provider repo — the applicability map is public and we will correct it.

Create-or-Update Ergonomics does not apply to this provider. The published contracts declare no write operations, and a read-only API cannot create-or-update. The facet is excluded from this provider's denominator entirely — not scored zero. A reference or data API is not deficient for being unable to upsert.

The six quality facets above are damped to 85 points between them, because the conditional facet above carries the other 15. That is why each facet's contribution is shown against a damped maximum: raising a quality facet moves the composite by 85% of its nominal weight, not 100%. The full arithmetic is at apis.io/rating/.

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Agent readiness — checks not met, largest first (exact, from this profile):

MCP Server +12 pts — deployment.mode + probe verdict on the mcp/ manifest, not the pointer; an unprobed slug falls back to authorship Ask about this →
Stable Error Semantics +8 pts — OpenAPI $refs a shared error schema across 4xx/5xx responses (verified), else common[].type includes ErrorCatalog / ErrorCodes / DeclineCodes Ask about this →
A2A Agent Card +8 pts — a2a/-a2a.yml manifest, graded on conformance.grade against A2A 1.0.0 Ask about this →
Registration Without a Human +6 pts — a `registration_endpoint` in the served RFC 8414 / OIDC discovery document Ask about this →
Delegated User Identity +6 pts — a served discovery document listing authorization_code in grant_types_supported (served), else an oauth2 authorizationCode flow or openIdConnect declared in an OpenAPI (documented) Ask about this →
Typed Event Surface +6 pts — AsyncAPI document, OR webhooks/callbacks objects in the as-published OpenAPI, OR common[].type includes Webhooks Ask about this →

6 more unmet checks in the Agent Readiness table above.

Kin Score — facets with the most composite points still available (weight × headroom):

Access Clarity scores 0.0 — up to +20.0 composite points Ask about this →
Developer Ergonomics scores 21.4 — up to +15.7 composite points Ask about this →
Operational Transparency scores 0.0 — up to +13.0 composite points Ask about this →

Each check links to what satisfies it. Publish the artifact, or tell us where it already lives, and the score moves on the next scoring run.

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Improve this rating by publishing the missing artifacts — every area above can be raised, and the full rubric is at apis.io/rating/. Every facet and dimension name above is a link: it opens that measurement's own page — what it means, the exact checks that feed it, how the whole catalog distributes on it, and the providers at the top of it. This rating is computed from the provider profile at artifacts.apis.io/opencitations/apis.yml: open an issue on github.com/api-evangelist/opencitations to ask a question or point us at an artifact you publish. Submit an artifact on GitHub — free → Manage your own listing — the Influence plan, $499/mo →

Standards implemented 2

Standards this provider implements or carries. De facto ones are profiled and measured by the API Commons; formal ones come from the standards directory and are linked by the provider's own tags. The evidence column says how each claim was established — not that it was made.

DOI

tagged — the provider's own APIs.json carries the standard as a tag; implementation not verified

OpenAPI

measured — observed by APIs.io (published)

APIs 6

Individual APIs this provider publishes, each with its own machine-readable definition.

OpenCitations SPARQL Endpoint

SPARQL endpoints for structured queries against the OpenCitations Meta and Index datasets. Provides access to the full Linked Open Data graph for both bibliographic metadata and...

OpenCitations Authors API

Operations for retrieving works by author

OpenCitations Citations API

Operations for retrieving citation metadata and counts

OpenCitations Editors API

Operations for retrieving works by editor

OpenCitations Metadata API

Operations for retrieving bibliographic metadata

OpenCitations References API

Operations for retrieving outgoing reference data

Open Collections 5

Open, tool-agnostic API collections (OpenAPI-derived and Bruno).

OpenCitations Index REST Authors API

OPEN COLLECTION

OpenCitations Index REST Authors Citations API

OPEN COLLECTION

OpenCitations Index REST Authors Editors API

OPEN COLLECTION

OpenCitations Index REST Authors Metadata API

OPEN COLLECTION

OpenCitations Index REST Authors References API

OPEN COLLECTION

Semantic Vocabularies 1

JSON-LD contexts and semantic vocabularies used across these APIs.

Opencitations Context

24 classes · 13 properties

JSON-LD

Spectral Rules 1

Spectral governance rulesets for linting and validating these APIs. Counts are the severity each rule declares, not results of running them.

OpenCitations API Rules

68 rules · 66 error-severity 1 warn-severity 1 info-severity

SPECTRAL

Examples 5

Example request and response payloads for these APIs.

Author Works

4 fields

EXAMPLE

Citation By Oci

4 fields

EXAMPLE

Citation Count

4 fields

EXAMPLE

Incoming Citations

5 fields

EXAMPLE

Metadata Lookup

4 fields

EXAMPLE

Security Posture 2

Authentication, domain security, vulnerability disclosure, and trust-center signals.

OpenCitations Authentication

apiKey · 1 scheme

SECURITY

OpenCitations Domain Security

TLSv1.3

SECURITY

Agentic Access (API Evangelist recommendations) 1

Recommended x-agentic-access execution contracts for AI agents.

OpenCitations Agentic Access

9 operations

9 operations · 0 acting

AGENTIC

Resources

Agent Surfaces 1

MCP servers, agent skills, and machine-readable catalogs

AgenticAccess

AgenticAccess

Access & Security 2

Authentication, authorization, and security posture

DomainSecurity

DomainSecurity

Authentication

Authentication

Company 1

The organization behind the API

Website

Website

Source (apis.yml)

name: OpenCitations
description: OpenCitations is an open science research infrastructure providing free access to scholarly bibliographic and
  citation data. It offers REST APIs for querying citation networks, DOI-based citation lookups, reference data, and bibliographic
  metadata from millions of research articles. All data is published under CC0 Public Domain Waiver for unrestricted reuse.
deliveryModel:
  model: unknown
  open_source: false
  commercial: false
  callable_host: true
  label: Delivery model not determined — needs a product licence on record
  confidence: low
  source:
  - openapi
  generated: '2026-08-28'
  method: derived
accessModel:
  pricing: unknown
  onboarding: unknown
  trial: false
  try_now: false
  public: false
  label: Unknown
  confidence: low
  source:
  - authentication
  - security
  generated: '2026-11-13'
  method: derived
image: https://opencitations.net/static/favicon.ico
url: https://opencitations.net
created: '2024-01-01'
modified: '2026-09-16'
specificationVersion: '0.23'
tags:
- Citations
- Scholarly
- Research
- Open Science
- Bibliometrics
- DOI
- Academic
apis:
- name: OpenCitations SPARQL Endpoint
  description: SPARQL endpoints for structured queries against the OpenCitations Meta and Index datasets. Provides access
    to the full Linked Open Data graph for both bibliographic metadata and citation entity data using the SPARQL query language.
  image: https://opencitations.net/static/favicon.ico
  humanURL: https://sparql.opencitations.net
  baseURL: https://sparql.opencitations.net
  tags:
  - SPARQL
  - Linked Open Data
  - RDF
  - Scholarly
  properties:
  - type: Documentation
    url: https://sparql.opencitations.net
  contact:
  - FN: OpenCitations
    email: contact@opencitations.net
    X-website: https://opencitations.net
- aid: opencitations:opencitations-authors-api
  name: OpenCitations Authors API
  description: Operations for retrieving works by author
  humanURL: https://api.opencitations.net/index/v2
  baseURL: https://api.opencitations.net/meta/v1
  baseurl_source: contract
  tags:
  - Authors
  properties:
  - type: OpenAPI
    url: openapi/opencitations-authors-api-openapi.yml
  - type: Documentation
    url: https://api.opencitations.net/index/v2
  - type: RateLimits
    url: https://kinlane.github.io/all/opencitations/rate-limits/index-api.html
  - type: Documentation
    url: https://api.opencitations.net/meta/v1
  - type: RateLimits
    url: https://kinlane.github.io/all/opencitations/rate-limits/meta-api.html
- aid: opencitations:opencitations-citations-api
  name: OpenCitations Citations API
  description: Operations for retrieving citation metadata and counts
  humanURL: https://api.opencitations.net/index/v2
  baseURL: https://api.opencitations.net/index/v2
  tags:
  - Citations
  properties:
  - type: OpenAPI
    url: openapi/opencitations-citations-api-openapi.yml
  - type: Documentation
    url: https://api.opencitations.net/index/v2
  - type: RateLimits
    url: https://kinlane.github.io/all/opencitations/rate-limits/index-api.html
  - type: Documentation
    url: https://api.opencitations.net/meta/v1
  - type: RateLimits
    url: https://kinlane.github.io/all/opencitations/rate-limits/meta-api.html
- aid: opencitations:opencitations-editors-api
  name: OpenCitations Editors API
  description: Operations for retrieving works by editor
  humanURL: https://api.opencitations.net/index/v2
  baseURL: https://api.opencitations.net/meta/v1
  baseurl_source: contract
  tags:
  - Editor
  tags_raw:
  - Editors
  properties:
  - type: OpenAPI
    url: openapi/opencitations-editors-api-openapi.yml
  - type: Documentation
    url: https://api.opencitations.net/index/v2
  - type: RateLimits
    url: https://kinlane.github.io/all/opencitations/rate-limits/index-api.html
  - type: Documentation
    url: https://api.opencitations.net/meta/v1
  - type: RateLimits
    url: https://kinlane.github.io/all/opencitations/rate-limits/meta-api.html
- aid: opencitations:opencitations-metadata-api
  name: OpenCitations Metadata API
  description: Operations for retrieving bibliographic metadata
  humanURL: https://api.opencitations.net/index/v2
  baseURL: https://api.opencitations.net/meta/v1
  baseurl_source: contract
  tags:
  - Metadata
  properties:
  - type: OpenAPI
    url: openapi/opencitations-metadata-api-openapi.yml
  - type: Documentation
    url: https://api.opencitations.net/index/v2
  - type: RateLimits
    url: https://kinlane.github.io/all/opencitations/rate-limits/index-api.html
  - type: Documentation
    url: https://api.opencitations.net/meta/v1
  - type: RateLimits
    url: https://kinlane.github.io/all/opencitations/rate-limits/meta-api.html
- aid: opencitations:opencitations-references-api
  name: OpenCitations References API
  description: Operations for retrieving outgoing reference data
  humanURL: https://api.opencitations.net/index/v2
  baseURL: https://api.opencitations.net/index/v2
  tags:
  - References
  properties:
  - type: OpenAPI
    url: openapi/opencitations-references-api-openapi.yml
  - type: Documentation
    url: https://api.opencitations.net/index/v2
  - type: RateLimits
    url: https://kinlane.github.io/all/opencitations/rate-limits/index-api.html
  - type: Documentation
    url: https://api.opencitations.net/meta/v1
  - type: RateLimits
    url: https://kinlane.github.io/all/opencitations/rate-limits/meta-api.html
maintainers:
- FN: OpenCitations
  email: contact@opencitations.net
  X-website: https://opencitations.net
common:
- type: Website
  url: https://opencitations.net
- type: AgenticAccess
  url: agentic-access/opencitations-agentic-access.yml
- type: DomainSecurity
  url: security/opencitations-domain-security.yml
- type: Authentication
  url: authentication/opencitations-authentication.yml

OpenCitations API — frequently asked questions

Does OpenCitations have an API?

Yes. APIs.io lists 6 APIs from OpenCitations, including OpenCitations SPARQL Endpoint, OpenCitations Authors API and OpenCitations Citations API, and 3 more.

Is there an OpenAPI specification for the OpenCitations API?

Yes. APIs.io indexes 5 OpenAPI specifications for OpenCitations, each linked for download from this page.

How do I authenticate with the OpenCitations API?

OpenCitations uses bearer-token authentication (apiKey · 1 scheme). The details are profiled on APIs.io as OpenCitations Authentication.

Is the OpenCitations API ready for AI agents?

OpenCitations has a Kin Score of 26.5 out of 100 (thin) and an Agent Readiness score of 26.6 (agent-aware), scored by API Evangelist on 2026-11-13.

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