paper-fetch

Fetch the legal open-access PDF for a paper given a DOI (or title). Tries multiple OA sources in priority order and stops at the first hit.

Agent-native. Structured JSON envelope on stdout, NDJSON progress on stderr, stable exit codes, machine-readable schema, TTY-aware format default, idempotent retries.

Resolution order

1. Unpaywall — https://api.unpaywall.org/v2/{doi}?email=$UNPAYWALL_EMAIL, read best_oa_location.url_for_pdf (skipped if UNPAYWALL_EMAIL not set)
2. Semantic Scholar — https://api.semanticscholar.org/graph/v1/paper/DOI:{doi}?fields=openAccessPdf,externalIds
3. arXiv — if externalIds.ArXiv present, https://arxiv.org/pdf/{arxiv_id}.pdf
4. PubMed Central OA — if PMCID present, https://www.ncbi.nlm.nih.gov/pmc/articles/{pmcid}/pdf/
5. bioRxiv / medRxiv — if DOI prefix is 10.1101, query https://api.biorxiv.org/details/{server}/{doi} for the latest version PDF URL
6. Otherwise → report failure with title/authors so the user can request via ILL

If only a title is given, resolve to a DOI first via Semantic Scholar search_paper_by_title (asta MCP) or Crossref.

Usage