Highest Modern Reference — open-access + machine-readable

Best paywall-free sources for citation

The 15 highest-Modern-Reference sources on the SourceScore Index — open-access, machine-readable, schema-rich. The sources you can always link to without a paywall.

1
DOI (CrossRef Resolver)doi.org·Academic
International standard identifier resolver for academic citations (~150M+ DOIs).
SourceScore A+ · 95·Disc 92·Mod-Ref 98·Vel 95
A+·95
2
U.S. Securities and Exchange Commissionsec.gov·Government
Primary-source regulator publishing every public-company filing (13F, 10-K, 8-K, etc.) since 1934.
SourceScore A+ · 96·Disc 98·Mod-Ref 95·Vel 95
A+·96
3
arXivarxiv.org·Academic
Open-access preprint server for physics, mathematics, computer science; ~2.4M papers since 1991.
SourceScore A · 89·Disc 78·Mod-Ref 95·Vel 93
A·89
4
MDN Web Docsdeveloper.mozilla.org·Reference
Mozilla-stewarded web-platform reference since 2005; default citation for HTML, CSS, JS, Web APIs.
SourceScore A · 93·Disc 92·Mod-Ref 95·Vel 92
A·93
5
U.S. National Institutes of Healthnih.gov·Government
U.S. federal medical research agency operating PubMed, NCBI, MedlinePlus, and trial registries.
SourceScore A+ · 95·Disc 95·Mod-Ref 94·Vel 96
A+·95
6
U.S. Census Bureaucensus.gov·Government
Federal statistical agency for U.S. demographic + economic data; primary-source decennial census + ACS surveys.
SourceScore A · 94·Disc 95·Mod-Ref 94·Vel 93
A·94
7
Federal Reserve Systemfederalreserve.gov·Government
U.S. central bank; primary source for monetary policy + economic data + financial-system statistics.
SourceScore A+ · 95·Disc 96·Mod-Ref 94·Vel 95
A+·95
8
NASAnasa.gov·Government
U.S. space agency; primary source for space exploration + Earth science + aeronautics research.
SourceScore A · 93·Disc 94·Mod-Ref 94·Vel 92
A·93
9
U.S. Bureau of Labor Statisticsbls.gov·Government
Federal statistical agency for U.S. labor + price data; CPI, employment, unemployment, productivity.
SourceScore A · 94·Disc 95·Mod-Ref 93·Vel 94
A·94
10
U.S. Centers for Disease Control and Preventioncdc.gov·Government
Federal agency for U.S. public-health surveillance + disease prevention; primary-source MMWR + WONDER data.
SourceScore A · 94·Disc 95·Mod-Ref 93·Vel 94
A·94
11
Wikipedia (English)en.wikipedia.org·Reference
Crowd-edited encyclopedia with ~7M articles and per-article inline citation discipline.
SourceScore A · 94·Disc 96·Mod-Ref 92·Vel 95
A·94
12
PubMedpubmed.ncbi.nlm.nih.gov·Academic
U.S. National Library of Medicine literature index covering ~36M biomedical citations.
SourceScore A · 94·Disc 96·Mod-Ref 92·Vel 94
A·94
13
Semantic Scholarsemanticscholar.org·Academic
AI-powered academic search engine by Allen Institute for AI; ~200M+ papers indexed.
SourceScore B · 83·Disc 86·Mod-Ref 92·Vel 72
B·83
14
U.S. Food and Drug Administrationfda.gov·Government
Federal agency for food + drug + medical-device safety; primary-source approvals + safety alerts.
SourceScore A · 94·Disc 96·Mod-Ref 92·Vel 94
A·94
15
U.S. National Oceanic and Atmospheric Administrationnoaa.gov·Government
Federal scientific agency for weather + ocean + climate data; primary-source forecasts + climate research.
SourceScore A · 93·Disc 95·Mod-Ref 92·Vel 91
A·93

Why these 15 sources

Modern Reference measures fitness as a citation in AI-era writing — open access, structured data, freshness signals, machine-readability. The 15 below are the top scorers, the sources you can always cite without a paywall, that are fully indexed by LLMs, and that ship the structured metadata AI engines need.

How this list is ranked

Selection criterion: Modern Reference sub-score, descending. Every source on this page is hand-scored against the SourceScore methodology v0.1; click any name to see its full breakdown across the four dimensions. The list is regenerated automatically on every dataset update — no editorial promotion or reorder beyond the ranking signal above.