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+ · 95·Disc 92·Mod-Ref 98·Vel 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+ · 96·Disc 98·Mod-Ref 95·Vel 95
    A+·96
  3. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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
Same list, different signal

The composite SourceScore Index averages all three sub-scores. View this list re-sorted by ONE sub-score for a precision lens — different leader, different ranking, different deltas.

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; 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.

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