SourceScore
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. 1
    DOI (CrossRef Resolver)doi.org·Academic

    International standard identifier resolver for academic citations (~150M+ DOIs).

    SourceScore A+ · 95Discipline 92Modern Reference 98Velocity 95
    A+·95
  2. 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+ · 96Discipline 98Modern Reference 95Velocity 95
    A+·96
  3. 3
    arXivarxiv.org·Academic

    Open-access preprint server for physics, mathematics, computer science; ~2.4M papers since 1991.

    SourceScore A · 89Discipline 78Modern Reference 95Velocity 93
    A·89
  4. 4
    MDN Web Docsdeveloper.mozilla.org·Reference

    Mozilla-stewarded web-platform reference since 2005; default citation for HTML, CSS, JS, Web APIs.

    SourceScore A · 93Discipline 92Modern Reference 95Velocity 92
    A·93
  5. 5
    U.S. National Institutes of Healthnih.gov·Government

    U.S. federal medical research agency operating PubMed, NCBI, MedlinePlus, and trial registries.

    SourceScore A+ · 95Discipline 95Modern Reference 94Velocity 96
    A+·95
  6. 6
    U.S. Census Bureaucensus.gov·Government

    Federal statistical agency for U.S. demographic + economic data; primary-source decennial census + ACS surveys.

    SourceScore A · 94Discipline 95Modern Reference 94Velocity 93
    A·94
  7. 7
    Federal Reserve Systemfederalreserve.gov·Government

    U.S. central bank; primary source for monetary policy + economic data + financial-system statistics.

    SourceScore A+ · 95Discipline 96Modern Reference 94Velocity 95
    A+·95
  8. 8
    NASAnasa.gov·Government

    U.S. space agency; primary source for space exploration + Earth science + aeronautics research.

    SourceScore A · 93Discipline 94Modern Reference 94Velocity 92
    A·93
  9. 9
    U.S. Bureau of Labor Statisticsbls.gov·Government

    Federal statistical agency for U.S. labor + price data; CPI, employment, unemployment, productivity.

    SourceScore A · 94Discipline 95Modern Reference 93Velocity 94
    A·94
  10. 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 · 94Discipline 95Modern Reference 93Velocity 94
    A·94
  11. 11
    Wikipedia (English)en.wikipedia.org·Reference

    Crowd-edited encyclopedia with ~7M articles and per-article inline citation discipline.

    SourceScore A · 94Discipline 96Modern Reference 92Velocity 95
    A·94
  12. 12
    PubMedpubmed.ncbi.nlm.nih.gov·Academic

    U.S. National Library of Medicine literature index covering ~36M biomedical citations.

    SourceScore A · 94Discipline 96Modern Reference 92Velocity 94
    A·94
  13. 13
    Semantic Scholarsemanticscholar.org·Academic

    AI-powered academic search engine by Allen Institute for AI; ~200M+ papers indexed.

    SourceScore B · 83Discipline 86Modern Reference 92Velocity 72
    B·83
  14. 14
    U.S. Food and Drug Administrationfda.gov·Government

    Federal agency for food + drug + medical-device safety; primary-source approvals + safety alerts.

    SourceScore A · 94Discipline 96Modern Reference 92Velocity 94
    A·94
  15. 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 · 93Discipline 95Modern Reference 92Velocity 91
    A·93
Same list, different signal

The SourceScore Index combines all three sub-scores. You can also see this list sorted by just one of them, which can change the order and the source at the top.

By Discipline →By Modern Reference →By Velocity →

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; tap any source to see its full breakdown across the three sub-scores and the overall Index. The list is regenerated automatically on every dataset update — no editorial promotion or reorder beyond the ranking signal above.

Frequently asked questions

Best paywall-free sources for citation?

By the SourceScore Index, the top 5: 1. DOI (CrossRef Resolver) (A+ 95/100); 2. U.S. Securities and Exchange Commission (A+ 96/100); 3. arXiv (A 89/100); 4. MDN Web Docs (A 93/100); 5. U.S. National Institutes of Health (A+ 95/100). Each is hand-scored on Citation Discipline, Modern Reference, and Citation Velocity — full ranking + breakdowns below.

Which source tops this list, and why?

DOI (CrossRef Resolver) ranks #1, scoring A+ (95/100) on the SourceScore Index — the highest composite citation-quality score here. International standard identifier resolver for academic citations (~150M+ DOIs).

How is this list ranked?

Ranked by Modern Reference sub-score, descending, scored against the SourceScore methodology v0.1 across Citation Discipline, Modern Reference (AI-era fitness), and Citation Velocity. Regenerated automatically on every dataset update — no paid placement or editorial promotion.

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