PMC BioC JSON ↗

Primary full-text source. Returns pre-labeled sections (TITLE, ABSTRACT, METHODS, CONCL).

NCBI E-Utilities Search ↗

PMC article search. Returns list of PMC IDs for a query term.

NCBI E-Utilities Fetch (JATS) ↗

JATS XML fallback for articles not in BioC open-access corpus.

OpenAlex ↗

PENDING. Free scholarly graph: 200M+ works, authors, institutions, concepts. No key required. Add mailto= polite header via OPENALEX_EMAIL env var. Primary data layer — covers ~90% of scholarly literature. Endpoints: /works /sources /authors /institutions. Docs: https://docs.openalex.org

Crossref REST API ↗

PENDING. DOI registration + metadata normalization. No key required. Add User-Agent mailto: header via CROSSREF_EMAIL. Essential for DOI resolution and deduplication. Endpoint: /works?query=... Docs: https://api.crossref.org

DOAJ API ↗

PENDING. Directory of Open Access Journals — vetted OA quality filter. No key required for read endpoints. Endpoints: /search/journals /search/articles. Use for journal whitelist and license credibility check. Docs: https://doaj.org/api/v4/docs

PLOS API ↗

PENDING. PLOS publisher API — immediate access, no signup. Endpoint: /search?q=... Returns JSON. Fields: title, abstract, author, journal, DOI. ~5 min to usable. Docs: https://api.plos.org

Springer Nature Open Access API ↗

PENDING. Major publisher OA API — requires account + API key. Key goes in api_key= query param. Register at: https://dev.springernature.com ~15-30 min setup. Strongest structured OA dataset from a major publisher.

Europe PMC ↗

PENDING. Biomedical full-text + MeSH annotations. No key required. Endpoint: /search?query=... Includes full-text XML where available. Covers life sciences. Docs: https://europepmc.org/RestfulWebService

Frontiers Search API ↗

PENDING. Frontiers publisher API — auth requirements unknown; verify stability. Check Swagger UI at base_url. Fallback: use OpenAlex filter if unstable. Confidence: medium.

OAI-PMH Harvester ↗

PENDING. Universal OAI-PMH harvesting protocol. Used by OJS journals, institutional repositories, and many independent publishers. Endpoint per journal is stored in journal_registry.oai_endpoint. Typical pattern: /oai or /oai/request or /index.php/journal/oai. verb=ListRecords&metadataPrefix=oai_dc for DC metadata; Use &from=DATE for incremental sync. No key required. This is the industry-standard ingestion protocol for independent journals.

Cambridge University Press API ↗

PENDING. Cambridge journals API — register at https://api.cambridge.org/register. Publisher-level journal metadata and content access. Use case: Cambridge-published peer-reviewed journals. Confidence: high (existence confirmed).

Unpaywall ↗

PENDING. DOI → OA full-text resolver. No key required; add email param. Given a DOI, returns best available OA full-text link (PMC, publisher, preprint). Endpoint: /v2/{doi}?email=YOUR_EMAIL. Critical for DOI-to-full-text pipeline after Crossref discovery. Docs: https://unpaywall.org/products/api

Elsevier ScienceDirect API ↗

CONDITIONAL. Major publisher — API exists but more controlled than OA options. Requires institutional token for full text. Register at: https://dev.elsevier.com Good for metadata + abstracts; full-text gated by institution. Confidence: medium (access depends on subscription).

Taylor & Francis API ↗

CONDITIONAL. API token available via admin portal. Primarily institutional/admin integrations rather than open scholarly API. Verify access at: https://help.tandfonline.com — search API Token. Confidence: low as fully open scholarly API.