OpenCitations API Guide

Overview

OpenCitations is an independent infrastructure organization dedicated to open scholarship and the publication of open bibliographic and citation data. Its main product, the OpenCitations Index of Crossref open DOI-to-DOI citations (COCI), contains over 1.6 billion citation relationships harvested from CrossRef metadata. This makes it the largest fully open citation dataset in the world.

The OpenCitations API allows researchers to programmatically access citation and reference data for any DOI in the index. This is valuable for citation network analysis, bibliometric research, impact assessment, and building literature discovery tools. Unlike proprietary citation databases (Web of Science, Scopus), OpenCitations data is fully open under a CC0 public domain dedication.

The API is free, requires no authentication, and has no published rate limits. It returns data in JSON or CSV format, making it easy to integrate into data analysis pipelines.

Authentication

No authentication required. The OpenCitations API is fully open and free. No API key, registration, or email is needed. There are no published rate limits, but users should implement reasonable request pacing for large-scale queries. For bulk data access, download the complete COCI dataset from https://opencitations.net/download.

Core Endpoints

Citations: Find Papers That Cite a DOI

• URL: GET https://api.opencitations.net/index/v1/citations/{doi}