OpenCitations Index and Meta API

Use in your agent

Load the citations to one DOI from OpenCitations into pandas and Parquet. Checked against the provider's documentation on Nov 3, 2026.

Access

• No token needed; set OPENCITATIONS_TOKEN to send a free access token in the authorization header, as OpenCitations encourages for code.
• Index API base https://api.opencitations.net/index/v2 (operations such as citations/doi:..., references/doi:..., citation-count/doi:...).

Request

curl 'https://api.opencitations.net/index/v2/citations/doi:10.1093/rfs/hhaa009'

Format

A JSON array (or CSV with format=csv) with one row per citation: oci, citing, cited, creation, timespan, journal_sc and author_sc. citing and cited list identifiers such as omid:, doi: and pmid:, separated by spaces.

Load into pandas and Parquet

Needs Python 3 with requests, pandas and pyarrow.

"""OpenCitations Index: citations to one DOI -> pandas -> Parquet. No token needed (an optional free access token is encouraged)."""
import os
import requests
import pandas as pd

DOI = "10.1093/rfs/hhaa009"
headers = {"authorization": os.environ["OPENCITATIONS_TOKEN"]} if os.environ.get("OPENCITATIONS_TOKEN") else {}
r = requests.get(f"https://api.opencitations.net/index/v2/citations/doi:{DOI}", headers=headers, timeout=90)
r.raise_for_status()
df = pd.DataFrame(r.json())
df.to_parquet("opencitations_citations.parquet", index=False)
print(len(df), "citations to", DOI, "; columns:", ",".join(df.columns))

Run by us on 2026-11-03 (python 3.13.5 | pandas 3.1.0 | pyarrow 26.0.0 | requests 2.34.2). Result: 1940 citations to 10.1093/rfs/hhaa009 ; columns: oci,citing,cited,creation,timespan,journal_sc,author_sc

Limits

• 180 requests per minute per IP address.
• Use the database dumps at download.opencitations.net for large-scale retrieval.

Quirks

• citing and cited hold several identifiers in one string; split on spaces and pick the doi: one.
• timespan is an ISO 8601 duration such as P2Y3M, and creation can be a year or a full date.

Terms and attribution

• All OpenCitations data is CC0 and may be reused for any purpose, including commercial purposes.

Sources

• https://api.opencitations.net/index/v2: “API calls are rate-limited to 180 requests/minute per IP address to ensure fair usage and service availability.”
• https://opencitations.net/: “The data held in any of the OpenCitations datasets are available under a Creative Commons public domain dedication (CC0).”
• https://api.opencitations.net/index/v2: “All the present operations return either a JSON document (default) or a CSV document according to the mimetype specified in the Accept header of the request.”