Yes. The Free tier is 600 requests a month at 100 requests a minute, across every endpoint in the catalogue, with no credit card. Nothing about it expires.

What happens when I hit the quota?

Requests return 429 with the limit, what you have used, and which window you tripped — nothing is queued, and nothing is charged. The monthly quota resets on the 1st (UTC). There is no rollover: unused requests do not carry into the next month.

Do failed requests use up my quota?

A 5xx does not. If a source breaks on our side, the request is excluded from your monthly count. A 4xx does count — a wrong parameter is still a request we answered. Per-minute throttling counts everything, so a retry loop is still throttled.

Which tier do I need?

Start on Free. Every response carries the remaining quota in its headers, and the dashboard reads the same number enforcement uses, so you will see the ceiling coming rather than discovering it.

How is Zapi different from RapidAPI or Apify?

Zapi focuses on a consistent REST contract — one API key, one response format, one error pattern for every source. No need to learn per-provider quirks like on traditional marketplaces, and no need to set up scraping workflows like on Apify.

What about the legality of accessing public data?

Zapi only accesses data that is publicly available without a login. Responsibility for how it is ultimately used stays with the developer — make sure your use case complies with the original source's ToS and the regulations in your operating region.

Is there an official SDK?

One: zpi-sdk, for TypeScript and JavaScript. It carries a typed error hierarchy, retries only what is safe to retry, submits bulk jobs, and verifies webhook signatures. Everything else is plain REST — cURL or any HTTP client works.

Can I request a source that isn’t in the catalogue yet?

Yes, through the community Discord, on any tier.

PubMed

NCBI E-utilities across 37 Entrez databases — literature search, summaries, full records, cross-database links, citation metrics and clinical trials.

22 endpoints163 calls21/22 passing

Get API key

Abstract

efetch db=pubmed&rettype=abstract&retmode=text, pre-bound. The payload is one numbered block per record; the split keys each block back to its PMID so the

GET/v1/research:pubmed/abstract

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Parameters

Name	Type	In	Description
id	string	query	Comma-separated PMIDs, max 200 per call. Required.

Example response

{"project":"research:pubmed",  "data": {"db":"pubmed","count":2,    "items": [      {"pmid":"33301246","content":"1. N Engl J Med. 2020 Dec 31;383(27):2603-2615. doi: 10.1056/NEJMoa2034577. Epub \n2020 Dec 10.\n\nSafety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine.\n\nPolack FP(1), Thomas SJ(…"      },      {"pmid":"32109013","content":"2. N Engl J Med. 2020 Apr 30;382(18):1708-1720. doi: 10.1056/NEJMoa2002032. Epub \n2020 Feb 28.\n\nClinical Characteristics of Coronavirus Disease 2019 in China.\n\nGuan WJ(1), Ni ZY(1)…"      }    ],"format":"text","provider":"pubmed"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Annotation Search

PubTator3 entity-aware search. Page size is the service's own, not ours — it reports page_size back and ignores any attempt to set it.

GET/v1/research:pubmed/annotation-search

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Parameters

Name	Type	In	Description
text	string	query	Free text, or a PubTator concept id such as @DISEASE_COVID_19 to search by entity. Required.
page	number	query	Page number. Default 1.
sort	enum	query	Result order. Default relevance. One of relevance, date.

Example response

{"project":"research:pubmed",  "data": {"page":1,"text":"covid-19 vaccine","count":10,    "items": [      {"doi":"10.14423/SMJ.0000000000001576","date":"2023-07-01T00:00:00Z","pmid":"37400094","issue":"7","pages":"519-523","score":291.16425,"title":"Associations between COVID-19 Death Exposure and COVID-19 Vaccine Hesitancy and Vaccine Uptake.","volume":"116",        "authors": [          "Andersen JA"        ],"journal":"South Med J","highlight":"Associations between @DISEASE_COVID_19 @DISEASE_MESH:D000086382 @@@<m>COVID</m>-<m>19</m> Death@@@ Exposure and <m>COVID</m>-<m>19</m> <m>Vaccine</m> Hesitancy and <m>Vaccine</m> U…","citationNlm":"Andersen JA, Scott AJ, Rowland B, Willis DE, McElfish PA. Associations between COVID-19 Death Exposure and COVID-19 Vaccine Hesitancy and Vaccine Uptake. South Med J. 2023 Jul;116(…","publishedOn":"2023 Jul","citationBibTeX":"@article{37400094, title={Associations between COVID-19 Death Exposure and COVID-19 Vaccine Hesitancy and Vaccine Uptake.}, author={Andersen JA and Scott AJ and Rowland B and Willi…"      }    ],"limit":10,"total":152737,    "facets": {      "type": [        {"name":"Journal Article","count":137431        }      ],      "year": [        {"name":"2022","count":43790        }      ],      "journal": [        {"name":"Vaccines (Basel)","count":5035        }      ]    },"hasMore":true,"nextPage":2,"provider":"pubmed"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Annotations

PubTator3 BioC-JSON export. The service answers 29 KB of browsable HTML on a default Accept and still says 200, so application/json is not optional here.

GET/v1/research:pubmed/annotations

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Parameters

Name	Type	In	Description
pmids	string	query	Comma-separated PMIDs, max 100 per call. Required.
full	enum	query	Annotate the full text instead of title and abstract. Default false. One of true, false.

Example response

{"project":"research:pubmed",  "data": {"count":2,    "items": [      {"pmid":"32109013","year":2020,"pmcid":"PMC7092819","authors":"Guan WJ, Ni ZY, Hu Y, Liang WH, Ou CQ, He JX, Liu L, Shan H, Lei CL, Hui DSC, Du B, Li LJ, Zeng G, Yuen KY, Chen RC, Tang CL, Wang T, Chen PY, Xiang J, Li SY, Wang JL, Liang ZJ, Pe…","journal":"N Engl J Med. 2020 Apr 30;382(18):1708-1720. doi: 10.1056/NEJMoa2002032. Epub ",        "passages": [          {"text":"Clinical Characteristics of Coronavirus Disease 2019 in China.","type":"title","offset":0,"section":null,            "annotations": [              {"id":"1","name":"COVID-19","text":"Coronavirus Disease 2019","type":"Disease","biotype":"disease","database":"ncbi_mesh","accession":"@DISEASE_COVID_19",                "locations": [                  {"span":24,"offset":28                  }                ],"identifier":"MESH:D000086382","normalizedId":"D000086382"              }            ]          }        ],"annotationCount":22      }    ],"fullText":false,"provider":"pubmed"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Citation Export

NCBI literature citation exporter. A PMID that does not exist answers 200 with a zero-byte body, so an empty response is a verdict here, not a transport failure.

GET/v1/research:pubmed/citation-export

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Parameters

Name	Type	In	Description
id	string	query	One PMID, or a PMC id when db is pmc. Required.
db	enum	query	Source collection. Default pubmed. One of pubmed, pmc.
format	enum	query	csl returns JSON, ris and medline return text. Default csl. One of csl, ris, medline.

Example response

{"project":"research:pubmed",  "data": {"db":"pubmed","id":"33301246","format":"csl",    "citation": {"id":"pmid:33301246","DOI":"10.1056/NEJMoa2034577","ISSN":"0028-4793","PMID":"33301246","page":"2603-2615","type":"article-journal","PMCID":"PMC7745181","issue":"27","title":"Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine",      "author": [        {"given":"Fernando P","family":"Polack"        },        {"given":"Stephen J","family":"Thomas"        },        {"given":"Nicholas","family":"Kitchin"        }      ],      "issued": {        "date-parts": [          [            2020,            12,            31          ]        ]      },"source":"PubMed","volume":"383",      "accessed": {        "date-parts": [          [            2026,            8,            29          ]        ]      },      "epub-date": {        "date-parts": [          [            2020,            12,            10          ]        ]      },"container-title":"The New England journal of medicine","publisher-place":"United States","container-title-short":"N Engl J Med"    },"provider":"pubmed"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Citation Match

ecitmatch answers plain text, one pipe-delimited line per citation, with the PMID appended after the caller's own key. A miss comes back as NOT_FOUND with a reason

GET/v1/research:pubmed/citation-match

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Parameters

Name	Type	In	Description
journal	string	query	Journal title or NLM abbreviation. Required.
year	number	query	Publication year. Required.
volume	string	query	Journal volume.
firstPage	string	query	First page of the article.
author	string	query	First author, surname and initials.
key	string	query	Your own label for this citation, echoed back on the match.

Example response

{"project":"research:pubmed",  "data": {"db":"pubmed","key":"ref1","pmid":"2014248","year":1991,"author":"mann bj","volume":"88","journal":"proc natl acad sci u s a","provider":"pubmed","firstPage":"3248"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Citation Metrics

iCite bibliometrics. It inlines cited_by[] and references[] — 841 KB for two PMIDs — so those arrays are opt-in rather than default.

GET/v1/research:pubmed/citation-metrics

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Parameters

Name	Type	In	Description
pmids	string	query	Comma-separated PMIDs, max 200 per call. Required.
includeCitationLists	enum	query	Include the full citedBy, citedByClinical and references PMID lists. They are large — two PMIDs measured 841 KB. Default false. One of true, false.

Example response

{"project":"research:pubmed",  "data": {"count":2,    "items": [      {"doi":"10.1056/NEJMoa2002032","pmid":"32109013","year":2020,"human":0.7777777777777778,"title":"Clinical Characteristics of Coronavirus Disease 2019 in China.","animal":0,"xCoord":-0.19245008972987523,"yCoord":0.6666666666666667,        "authors": [          {"name":"Guan, Wei-Jie","lastName":"Guan","firstName":"Wei-Jie"          }        ],"journal":"N Engl J Med","isClinical":false,"provisional":false,"citationCount":18784,"nihPercentile":100,"citationsPerYear":3130.6666666666665,"fieldCitationRate":5.71715931843237,"isResearchArticle":true,"molecularCellular":0.2222222222222222,"relativeCitationRatio":1178.3415335154866,"citedByClinicalArticle":true,"expectedCitationsPerYear":2.656841482389724,"approximatePotentialToTranslate":0.95      }    ],"provider":"pubmed","includeCitationLists":false  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Database Info

einfo per-database record: searchable fields, link names, build and record count.

GET/v1/research:pubmed/database-info

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Parameters

Name	Type	In	Description
db	enum	query	Entrez database to describe. One of pubmed, protein, nuccore, ipg, nucleotide, structure, genome, grasp, annotinfo, assembly, bioproject, biosample, blastdbinfo, books, cdd, clinvar, dbvar, gene, gds, geoprofiles, medgen, mesh, nlmcatalog, omim, orgtrack, pmc, proteinclusters, pcassay, protfam, pccompound, pcsubstance, seqannot, snp, sra, taxonomy, biocollections, gtr. Required.

Example response

{"project":"research:pubmed",  "data": {"db":"pubmed","build":"Build-2026.08.29.12.19",    "links": [      {"dbTo":"assembly","menu":"Assembly","name":"pubmed_assembly","description":"Assembly"      },      {"dbTo":"bioproject","menu":"Project Links","name":"pubmed_bioproject","description":"Related Projects"      }    ],    "fields": [      {"name":"ALL","isDate":false,"fullName":"All Fields","isHidden":false,"hierarchy":false,"termCount":null,"description":"All terms from all searchable fields","isNumerical":false,"singleToken":false      },      {"name":"UID","isDate":false,"fullName":"UID","isHidden":true,"hierarchy":false,"termCount":null,"description":"Unique number assigned to publication","isNumerical":true,"singleToken":true      }    ],"menuName":"PubMed","provider":"pubmed","linkCount":47,"fieldCount":48,"lastUpdate":"2026/08/29 12:19","description":"PubMed bibliographic record","recordCount":41081950  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Databases

NCBI's 429 body echoes our egress address back inside an `api-key` field.

GET/v1/research:pubmed/databases

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Parameters

No parameters. Call it as is.

Example response

{"project":"research:pubmed",  "data": {"count":37,    "items": [      {"db":"pubmed"      },      {"db":"protein"      },      {"db":"nuccore"      },      {"db":"ipg"      },      {"db":"nucleotide"      },      {"db":"structure"      },      {"db":"genome"      },      {"db":"grasp"      }    ],"provider":"pubmed"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Entity Autocomplete

PubTator3 concept suggestions. The `_id` it returns is the accession the search and relations endpoints take, so it is surfaced as `conceptId` rather than dropped.

GET/v1/research:pubmed/entity-autocomplete

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Parameters

Name	Type	In	Description
query	string	query	Partial entity name to complete. Required.
concept	enum	query	Restrict suggestions to one entity type. One of gene, disease, chemical, species, variant, cellline.
limit	number	query	Maximum suggestions to return. Default 10.

Example response

{"project":"research:pubmed",  "data": {"count":10,    "items": [      {"name":"COVID-19","biotype":"disease","database":"ncbi_mesh","conceptId":"@DISEASE_COVID_19","matchedOn":"Matched on name COVID-19","databaseId":"D000086382","description":null      },      {"name":"Post-Acute COVID-19 Syndrome","biotype":"disease","database":"ncbi_mesh","conceptId":"@DISEASE_Post_Acute_COVID_19_Syndrome","matchedOn":"Multiple matches","databaseId":"D000094024","description":null      },      {"name":"pediatric multisystem inflammatory disease COVID-19 related","biotype":"disease","database":"ncbi_mesh","conceptId":"@DISEASE_pediatric_multisystem_inflammatory_disease_COVID_19_related","matchedOn":"Multiple matches","databaseId":"C000705967","description":null      }    ],"query":"covid","provider":"pubmed"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Entity Relations

PubTator3 curated relations. An unfiltered e1 can answer 158 KB, so the result is capped here and the upstream length is reported alongside it.

GET/v1/research:pubmed/entity-relations

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Parameters

Name	Type	In	Description
e1	string	query	First concept id, from entity-autocomplete. Required.
type	enum	query	Relation type. Default ANY. One of ANY, treat, cause, cotreat, compare, interact, inhibit, stimulate, drug_interact, associate, prevent, positive_correlate, negative_correlate.
e2	string	query	Second concept id, to pin both ends of the relation.
limit	number	query	Maximum relations to return. Default 100.

Example response

{"project":"research:pubmed",  "data": {"e1":"@CHEMICAL_Doxorubicin","e2":"@DISEASE_Neoplasms","type":"treat","count":1,    "items": [      {"type":"treat","source":"@CHEMICAL_Doxorubicin","target":"@DISEASE_Neoplasms","publications":14872      }    ],"limit":3,"total":1,"provider":"pubmed"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Fetch Records

efetch: full records. The payload is XML, MEDLINE text or FASTA depending on rettype — never JSON — so it is handed back verbatim rather than half-parsed.

GET/v1/research:pubmed/fetch-records

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Parameters

Name	Type	In	Description
id	string	query	Comma-separated UIDs, max 200 per call. Required.
db	enum	query	Entrez database. Default pubmed. One of pubmed, protein, nuccore, ipg, nucleotide, structure, genome, grasp, annotinfo, assembly, bioproject, biosample, blastdbinfo, books, cdd, clinvar, dbvar, gene, gds, geoprofiles, medgen, mesh, nlmcatalog, omim, orgtrack, pmc, proteinclusters, pcassay, protfam, pccompound, pcsubstance, seqannot, snp, sra, taxonomy, biocollections, gtr.
rettype	enum	query	Record type. Valid values depend on the database. One of abstract, medline, uilist, fasta, gb, gp, docsum, full, native, xml.
retmode	enum	query	Payload encoding. Default xml. One of xml, text, asn.1.
retstart	number	query	Offset into the record set when fetching from history.
retmax	number	query	Maximum records to return. Upstream caps at 10000.
strand	enum	query	Sequence strand, 1 plus and 2 minus. Sequence databases only. One of 1, 2.
seqStart	number	query	First sequence base to retrieve. Sequence databases only.
seqStop	number	query	Last sequence base to retrieve. Sequence databases only.

Example response

{"project":"research:pubmed",  "data": {"db":"pubmed",    "ids": [      "33301246",      "32109013"    ],"type":"medline","bytes":206336,"format":"xml","content":"<?xml version=\"1.0\" ?>\n<!DOCTYPE PubmedArticleSet PUBLIC \"-//NLM//DTD PubMedArticle, 1st January 2025//EN\" \"https://dtd.nlm.nih.gov/ncbi/pubmed/out/pubmed_250101.dtd\">\n<PubmedArtic…","provider":"pubmed"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Gene Report

NCBI Datasets v2 gene record. A symbol that does not exist answers 200 with an empty object, so an empty body is the not-found signal.

GET/v1/research:pubmed/gene-report/:symbol/:taxon

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Parameters

Name	Type	In	Description
symbol	string	path	Official gene symbol. Required.
taxon	string	path	NCBI taxonomy id or organism name. Default 9606, human.
includeGeneOntology	enum	query	Include the full GO term set, which dominates the payload. Default false. One of true, false.

Example response

{"project":"research:pubmed",  "data": {"type":"PROTEIN_CODING","query":"TP53","taxId":"9606","taxon":"9606","geneId":"7157","symbol":"TP53",    "omimIds": [      "191170"    ],    "summary": [      {"source":null,"description":"This gene encodes a tumor suppressor protein containing transcriptional activation, DNA binding, and oligomerization domains. The encoded protein responds to diverse cellular stres…"      }    ],"taxName":"Homo sapiens","provider":"pubmed",    "synonyms": [      "P53"    ],"commonName":"human",    "geneGroups": [      {"id":"7157","method":"NCBI Ortholog"      }    ],"matchCount":1,    "annotations": [      {"releasedOn":"2025-08-01","assemblyName":"GRCh38.p14","annotationName":"GCF_000001405.40-RS_2025_08",        "genomicLocations": [          {"sequenceName":"17","accessionVersion":"NC_000017.11"          }        ],"assemblyAccession":"GCF_000001405.40"      }    ],    "chromosomes": [      "17"    ],"description":"tumor protein p53","orientation":"minus",    "mapLocations": [      {"type":"Cytogenetic","value":"17p13.1"      }    ],"proteinCount":25,    "alternateNames": [      "antigen NY-CO-13"    ],    "ensemblGeneIds": [      "ENSG00000141510"    ],"nomenclatureId":"HGNC:11998","transcriptCount":26,    "referenceStandards": [      {"type":"REFSEQ_GENE",        "range": [          {"end":"24149","begin":"5001","orientation":"plus"          }        ],"accessionVersion":"NG_017013.2"      }    ],    "swissProtAccessions": [      "P04637"    ],    "transcriptTypeCounts": [      {"type":"PROTEIN_CODING","count":25      }    ],"nomenclatureAuthority":"HGNC"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Id Convert

PMC ID converter. It rejects a mixed batch with a 400, so the id type is declared and every value checked against it before the call. Its `email is missing` warning

GET/v1/research:pubmed/id-convert

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Parameters

Name	Type	In	Description
ids	string	query	Comma-separated ids, all of the same type, max 200. Required.
idtype	enum	query	Type of every id in the batch — mixed types are rejected. One of pmid, pmcid, doi, mid. Required.
versions	enum	query	Include every PMC version of the record. Default false. One of true, false.

Example response

{"project":"research:pubmed",  "data": {"count":2,    "items": [      {"doi":"10.1056/NEJMoa2034577","mid":null,"pmid":"33301246","pmcid":"PMC7745181","reason":null,"status":null,"requestedId":"33301246"      },      {"doi":"10.1056/NEJMoa2002032","mid":null,"pmid":"32109013","pmcid":"PMC7092819","reason":null,"status":null,"requestedId":"32109013"      }    ],"idType":"pmid","provider":"pubmed"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Link Check

elink acheck/ncheck/lcheck: which link types exist for a UID, without pulling the links themselves. acheck answers with a per-id catalogue, ncheck and lcheck

GET/v1/research:pubmed/link-check

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Parameters

Name	Type	In	Description
id	string	query	Comma-separated source UIDs, max 100 per call. Required.
dbfrom	enum	query	Source database. Default pubmed. One of pubmed, protein, nuccore, ipg, nucleotide, structure, genome, grasp, annotinfo, assembly, bioproject, biosample, blastdbinfo, books, cdd, clinvar, dbvar, gene, gds, geoprofiles, medgen, mesh, nlmcatalog, omim, orgtrack, pmc, proteinclusters, pcassay, protfam, pccompound, pcsubstance, seqannot, snp, sra, taxonomy, biocollections, gtr.
cmd	enum	query	acheck lists every link type, ncheck reports whether related records exist, lcheck whether external LinkOut providers exist. Default acheck. One of acheck, ncheck, lcheck.

Example response

{"project":"research:pubmed",  "data": {"cmd":"acheck",    "ids": [      "33301246",      "32109013"    ],"count":2,    "items": [      {"id":"33301246","count":13,        "links": [          {"dbTo":"books","htmlTag":"Cited in Books","menuTag":"Cited in Books","linkName":"pubmed_books_refs","priority":185          },          {"dbTo":"medgen","htmlTag":"MedGen","menuTag":"MedGen","linkName":"pubmed_medgen","priority":128          },          {"dbTo":"pmc","htmlTag":null,"menuTag":"PMC Links","linkName":"pubmed_pmc","priority":175          }        ]      },      {"id":"32109013","count":12,        "links": [          {"dbTo":"books","htmlTag":"Cited in Books","menuTag":"Cited in Books","linkName":"pubmed_books_refs","priority":185          },          {"dbTo":"pmc","htmlTag":null,"menuTag":"PMC Links","linkName":"pubmed_pmc","priority":175          },          {"dbTo":"pmc","htmlTag":"Free in PMC","menuTag":null,"linkName":"pubmed_pmc_local","priority":175          }        ]      }    ],"dbFrom":"pubmed","provider":"pubmed"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Link Provider

elink llinks/prlinks: LinkOut provider URLs. Icon paths come back host-relative, so they are resolved against NCBI's own host to stay usable.

GET/v1/research:pubmed/link-provider

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Parameters

Name	Type	In	Description
id	string	query	Comma-separated source UIDs, max 100 per call. Required.
dbfrom	enum	query	Source database. Default pubmed. One of pubmed, protein, nuccore, ipg, nucleotide, structure, genome, grasp, annotinfo, assembly, bioproject, biosample, blastdbinfo, books, cdd, clinvar, dbvar, gene, gds, geoprofiles, medgen, mesh, nlmcatalog, omim, orgtrack, pmc, proteinclusters, pcassay, protfam, pccompound, pcsubstance, seqannot, snp, sra, taxonomy, biocollections, gtr.
cmd	enum	query	llinks returns every LinkOut provider, prlinks only the publisher full-text links. Default llinks. One of llinks, prlinks.

Example response

{"project":"research:pubmed",  "data": {"cmd":"llinks",    "ids": [      "33301246"    ],"count":1,    "items": [      {"id":"33301246","count":9,        "links": [          {"url":"https://www.nejm.org/doi/10.1056/NEJMoa2034577?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub  0pubmed","iconUrl":"https://www.ncbi.nlm.nih.gov/corehtml/query/egifs/https:--www.nejm.org-pb-assets-images-editorial-icons-nejm-full-text.gif","linkName":null,            "attributes": [              "subscription/membership/fee required"            ],            "categories": [              "Full Text Sources"            ],"providerId":"4487","providerAbbr":"ATYPON","providerName":"Atypon"          },          {"url":"https://clinicaltrials.gov/search?term=AREA%5BReferencePMID%5D33301246","iconUrl":null,"linkName":null,            "attributes": [              "free resource"            ],            "categories": [              "Medical"            ],"providerId":"3654","providerAbbr":"CTgov","providerName":"ClinicalTrials.gov"          }        ]      }    ],"dbFrom":"pubmed","provider":"pubmed"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Link

elink neighbour modes. cmd=neighbor_score returned 310 KB for a single PMID, so maxLinks caps each link array before the payload rather than after it.

GET/v1/research:pubmed/link

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Parameters

Name	Type	In	Description
id	string	query	Comma-separated source UIDs, max 100 per call. Required.
dbfrom	enum	query	Source database. Default pubmed. One of pubmed, protein, nuccore, ipg, nucleotide, structure, genome, grasp, annotinfo, assembly, bioproject, biosample, blastdbinfo, books, cdd, clinvar, dbvar, gene, gds, geoprofiles, medgen, mesh, nlmcatalog, omim, orgtrack, pmc, proteinclusters, pcassay, protfam, pccompound, pcsubstance, seqannot, snp, sra, taxonomy, biocollections, gtr.
db	enum	query	Target database. Defaults to dbfrom. One of pubmed, protein, nuccore, ipg, nucleotide, structure, genome, grasp, annotinfo, assembly, bioproject, biosample, blastdbinfo, books, cdd, clinvar, dbvar, gene, gds, geoprofiles, medgen, mesh, nlmcatalog, omim, orgtrack, pmc, proteinclusters, pcassay, protfam, pccompound, pcsubstance, seqannot, snp, sra, taxonomy, biocollections, gtr.
cmd	enum	query	Link mode. neighbor_score adds a relatedness score. Default neighbor. One of neighbor, neighbor_score, neighbor_history.
linkname	string	query	Restrict to one named link set.
maxLinks	number	query	Cap on links kept per link set. Default 200.

Example response

{"project":"research:pubmed",  "data": {"db":"pmc","cmd":"neighbor",    "ids": [      "33301246"    ],"count":1,    "items": [      {"dbTo":"pmc","count":1,        "links": [          {"id":"7745181"          }        ],"dbFrom":"pubmed","linkName":"pubmed_pmc",        "sourceIds": [          "33301246"        ],"truncated":false      }    ],"dbFrom":"pubmed","webEnv":null,"maxLinks":3,"provider":"pubmed"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Post

epost stores a UID set on the history server and answers XML. The webEnv and queryKey it returns are what search, summary and fetch chain against for sets

GET/v1/research:pubmed/post

slow · 0.7s5m cache

Parameters

Name	Type	In	Description
id	string	query	Comma-separated UIDs to store, max 5000 per call. Required.
db	enum	query	Entrez database. Default pubmed. One of pubmed, protein, nuccore, ipg, nucleotide, structure, genome, grasp, annotinfo, assembly, bioproject, biosample, blastdbinfo, books, cdd, clinvar, dbvar, gene, gds, geoprofiles, medgen, mesh, nlmcatalog, omim, orgtrack, pmc, proteinclusters, pcassay, protfam, pccompound, pcsubstance, seqannot, snp, sra, taxonomy, biocollections, gtr.
webEnv	string	query	Append to an existing history session.

Example response

{"project":"research:pubmed",  "data": {"db":"pubmed",    "ids": [      "33301246",      "32109013"    ],"count":2,"webEnv":"MCID_6a93083700b9b9ef110c4022","provider":"pubmed","queryKey":"1","invalidIds":[]  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Search

esearch: term -> UID list. The 10,000-record window is upstream's, not ours; past it the history server (usehistory + epost) is the only way through.

GET/v1/research:pubmed/search

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Parameters

Name	Type	In	Description
term	string	query	Entrez query. Supports field tags such as [au], [ti], [mesh] and boolean operators. Required.
db	enum	query	Entrez database. Default pubmed. One of pubmed, protein, nuccore, ipg, nucleotide, structure, genome, grasp, annotinfo, assembly, bioproject, biosample, blastdbinfo, books, cdd, clinvar, dbvar, gene, gds, geoprofiles, medgen, mesh, nlmcatalog, omim, orgtrack, pmc, proteinclusters, pcassay, protfam, pccompound, pcsubstance, seqannot, snp, sra, taxonomy, biocollections, gtr.
page	number	query	Page number. Default 1.
limit	number	query	UIDs per page. Default 20, max 500.
sort	enum	query	Sort order. Default is the database default. One of relevance, pubDate, author, journalName, mostRecent.
field	string	query	Limit the whole term to one search field.
datetype	enum	query	Date field the range applies to. One of pdat, edat, mdat.
mindate	string	query	Range start, YYYY/MM/DD.
maxdate	string	query	Range end, YYYY/MM/DD.
reldate	number	query	Limit to the last N days instead of a range.
usehistory	enum	query	Store the result set on the history server and return webEnv/queryKey. One of true, false.

Example response

{"project":"research:pubmed",  "data": {"db":"pubmed","page":1,"term":"covid-19 vaccine","count":0,"items":[],"limit":3,"total":0,"webEnv":"MCID_6a937c9f6cbc51515203019e","hasMore":false,"nextPage":null,"provider":"pubmed","queryKey":"1",    "warnings": [      "No items found."    ],"translations":[],"queryTranslation":"\"covid-19\"[Title] AND \"vaccine\"[Title] AND 2020/01/01:2021/12/31[Date - Publication] AND 2026/07/30:2026/08/29[Date - Publication]"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Spell

espell is XML-only: retmode=json answers HTTP 500 with a zero-byte body, so the response is parsed by regex rather than asked for in another format.

GET/v1/research:pubmed/spell

passing · 0.3s5m cache

Parameters

Name	Type	In	Description
term	string	query	Query to spell-check against the database index. Required.
db	enum	query	Entrez database. Default pubmed. One of pubmed, protein, nuccore, ipg, nucleotide, structure, genome, grasp, annotinfo, assembly, bioproject, biosample, blastdbinfo, books, cdd, clinvar, dbvar, gene, gds, geoprofiles, medgen, mesh, nlmcatalog, omim, orgtrack, pmc, proteinclusters, pcassay, protfam, pccompound, pcsubstance, seqannot, snp, sra, taxonomy, biocollections, gtr.

Example response

{"project":"research:pubmed",  "data": {"db":"pubmed","term":"fiberblast cell grwth",    "items": [      {"text":"","type":"original"      },      {"text":"fibroblast","type":"replaced"      },      {"text":" cell ","type":"original"      },      {"text":"growth","type":"replaced"      }    ],"provider":"pubmed","corrected":true,"correctedTerm":"fibroblast cell growth","replacementCount":2  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Summary

esummary: document summaries by UID. NCBI's summary keys are all-lowercase and db-specific, so the whole record is renamed rather than cherry-picked — dropping

GET/v1/research:pubmed/summary

failed last check5m cache

Parameters

Name	Type	In	Description
id	string	query	Comma-separated UIDs, max 200 per call. Required.
db	enum	query	Entrez database. Default pubmed. One of pubmed, protein, nuccore, ipg, nucleotide, structure, genome, grasp, annotinfo, assembly, bioproject, biosample, blastdbinfo, books, cdd, clinvar, dbvar, gene, gds, geoprofiles, medgen, mesh, nlmcatalog, omim, orgtrack, pmc, proteinclusters, pcassay, protfam, pccompound, pcsubstance, seqannot, snp, sra, taxonomy, biocollections, gtr.
version	enum	query	Summary schema version. Default 2.0. One of 1.0, 2.0.

Example response

{"project":"research:pubmed",  "data": {"db":"pubmed","count":2,    "items": [      {"uid":"33301246","essn":"1533-4406","issn":"0028-4793","issue":"27","pages":"2603-2615","title":"Safety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine.","medium":"","source":"N Engl J Med","volume":"383",        "authors": [          {"name":"Polack FP","authType":"Author","clusterId":""          }        ],"chapter":"","docDate":"","docType":"citation","edition":"",        "history": [          {"date":"2020/12/11 06:00","pubStatus":"pubmed"          }        ],"pubDate":"2020 Dec 31","srcDate":"","bookName":"","ePubDate":"2020 Dec 10",        "pubTypes": [          "Clinical Trial, Phase II"        ],"bookTitle":"",        "languages": [          "eng"        ],"pubStatus":"256","sortTitle":"safety and efficacy of the bnt162b2 mrna covid 19 vaccine",        "articleIds": [          {"value":"33301246","idType":"pubmed","idTypeNum":1          }        ],        "attributes": [          "Has Abstract"        ],"lastAuthor":"Gruber WC",        "references": [          {"note":"","pmid":33301245,"refType":"Comment in","refSource":"N Engl J Med. 2020 Dec 31;383(27):2677-2678. doi: 10.1056/NEJMe2034717."          }        ],"eLocationId":"doi: 10.1056/NEJMoa2034577","nlmUniqueId":"0255562","pmcRefCount":13,"sortPubDate":"2020/12/31 00:00","recordStatus":"PubMed - indexed for MEDLINE","reportNumber":"","locationLabel":"","publisherName":"","fullJournalName":"The New England journal of medicine","sortFirstAuthor":"Polack FP","vernacularTitle":"","availableFromUrl":"","publisherLocation":""      }    ],"provider":"pubmed"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Trials Detail

One ClinicalTrials.gov v2 study. The single-study record carries 140 scalar paths across four sections; the heavy repeated blocks (arms, outcomes, locations) are

GET/v1/research:pubmed/trials-detail/:nctId

passing · 0.4s5m cache

Parameters

Name	Type	In	Description
nctId	string	path	ClinicalTrials.gov registry id. Required.

Example response

{"project":"research:pubmed",  "data": {"sex":"ALL","nctId":"NCT04280705",    "phases": [      "PHASE3"    ],"status":"COMPLETED","acronym":null,"masking":"DOUBLE",    "keywords": [      "Adaptive"    ],"provider":"pubmed",    "armGroups": [      {"type":"PLACEBO_COMPARATOR","label":"Placebo","description":"200 mg of Remdesivir placebo administered intravenously on Day 1, followed by a 100 mg once-daily maintenance dose of Remdesivir placebo while hospitalized for up to a 10 days tota…",        "interventionNames": [          "Other: Placebo"        ]      }    ],    "locations": [      {"zip":"35233","city":"Birmingham","state":"Alabama","status":null,"country":"United States","facility":"University of Alabama at Birmingham School of Medicine - Infectious Disease","latitude":33.52066,"longitude":-86.80249      }    ],"startDate":"2020-02-21","studyType":"INTERVENTIONAL",    "whoMasked": [      "PARTICIPANT"    ],"allocation":"RANDOMIZED","briefTitle":"Adaptive COVID-19 Treatment Trial (ACTT)",    "conditions": [      "COVID-19"    ],"enrollment":1062,"hasResults":true,"ipdSharing":null,"maximumAge":"99 Years","minimumAge":"18 Years","orgStudyId":"20-0006",    "references": [      {"pmid":"38657001","type":"DERIVED","citation":"Singh K, Rubenstein K, Callier V, Shaw-Saliba K, Rupert A, Dewar R, Laverdure S, Highbarger H, Lallemand P, Huang ML, Jerome KR, Sampoleo R, Mills MG, Greninger AL, Juneja K, Porte…"      }    ],"whyStopped":null,"leadSponsor":"National Institute of Allergy and Infectious Diseases (NIAID)","briefSummary":"This study is an adaptive, randomized, double-blind, placebo-controlled trial to evaluate the safety and efficacy of novel therapeutic agents in hospitalized adults diagnosed with …","organization":"National Institute of Allergy and Infectious Diseases (NIAID)","secondaryIds":[],    "standardAges": [      "ADULT"    ],"collaborators":[],"firstPostedOn":"2020-02-21",    "interventions": [      {"name":"Placebo","type":"OTHER","description":"The supplied placebo lyophilized formulation is identical in physical appearance to the active lyophilized formulation and contains the same inactive ingredients. Alternatively, a …",        "armGroupLabels": [          "Placebo"        ]      }    ],"lastUpdatedOn":"2022-03-14","locationCount":60,"officialTitle":"A Multicenter, Adaptive, Randomized Blinded Controlled Trial of the Safety and Efficacy of Investigational Therapeutics for the Treatment of COVID-19 in Hospitalized Adults","otherOutcomes":[],"completionDate":"2020-05-21","enrollmentType":"ACTUAL",    "meshConditions": [      {"id":"D000086382","term":"COVID-19"      }    ],"primaryPurpose":"TREATMENT","oversightHasDmc":null,    "primaryOutcomes": [      {"measure":"Time to Recovery","timeFrame":"Day 1 through Day 29","description":"Day of recovery is defined as the first day on which the subject satisfies one of the following three categories from the ordinal scale: 1) Hospitalized, not requiring supplemental…"      }    ],"leadSponsorClass":"NIH","responsibleParty":"SPONSOR","statusVerifiedOn":"2020-04","healthyVolunteers":false,"interventionModel":"PARALLEL",    "meshInterventions": [      {"id":"C000606551","term":"remdesivir"      }    ],"organizationClass":"NIH",    "secondaryOutcomes": [      {"measure":"Change From Baseline in Alanine Transaminase (ALT)","timeFrame":"Days 1, 3, 5, 8, 11, 15 and 29","description":"Blood to evaluate ALT was collected at Days 1, 3, 5, 8, and 11 while participants were inpatient, and at Days 15 and 29, with the Day 1 assessment serving as baseline. Participants…"      }    ],"isFdaRegulatedDrug":true,"detailedDescription":"This study is an adaptive, randomized, double-blind, placebo-controlled trial to evaluate the safety and efficacy of novel therapeutic agents in hospitalized adults diagnosed with …","eligibilityCriteria":"Inclusion Criteria:\n\n1. Admitted to a hospital with symptoms suggestive of COVID-19 infection.\n2. Subject (or legally authorized representative) provides informed consent prior to …","isFdaRegulatedDevice":false,"resultsFirstPostedOn":"2020-09-25","primaryCompletionDate":"2020-05-21"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Trials Search

ClinicalTrials.gov v2 study search. v2 paginates by an opaque token, not a page number, so the cursor is passed through instead of being faked into a page index.

GET/v1/research:pubmed/trials-search

passing · 0.3s5m cache

Parameters

Name	Type	In	Description
condition	string	query	Condition or disease being studied.
term	string	query	Free-text terms matched across the whole record.
status	enum	query	Restrict to one recruitment status. One of NOT_YET_RECRUITING, RECRUITING, ENROLLING_BY_INVITATION, ACTIVE_NOT_RECRUITING, SUSPENDED, TERMINATED, COMPLETED, WITHDRAWN, AVAILABLE, NO_LONGER_AVAILABLE, TEMPORARILY_NOT_AVAILABLE, APPROVED_FOR_MARKETING, WITHHELD, UNKNOWN.
limit	number	query	Studies per page. Default 20, max 100.
cursor	string	query	Page token from nextCursor of a previous call.

Example response

{"project":"research:pubmed",  "data": {"term":null,"count":3,    "items": [      {"nctId":"NCT01128829",        "phases": [          "NA"        ],"status":"COMPLETED","acronym":"SIR","masking":"NONE",        "keywords": [          "obesity"        ],"startDate":"2010-05","studyType":"INTERVENTIONAL","allocation":"RANDOMIZED","briefTitle":"Sugar-replacement Sweeteners, and Blood Sugar Control",        "conditions": [          "Obesity"        ],"enrollment":17,"hasResults":true,"leadSponsor":"Washington University School of Medicine","briefSummary":"Several sugar-replacement sweeteners are currently on the market, including saccharine (ex. Sweet'N Low), aspartame (ex. Equal), and sucralose (ex. Splenda). The purpose of this st…","organization":"Washington University School of Medicine","firstPostedOn":"2010-05-24","lastUpdatedOn":"2014-12-22","officialTitle":"Regulation of Incretin Release by Non-nutritive Sweeteners in Humans","completionDate":"2012-10","enrollmentType":"ACTUAL","primaryPurpose":"BASIC_SCIENCE","leadSponsorClass":"OTHER","statusVerifiedOn":"2014-12","interventionModel":"CROSSOVER","primaryCompletionDate":"2012-02"      }    ],"limit":3,"total":15144,"cursor":null,"status":"COMPLETED","hasMore":true,"provider":"pubmed","condition":"diabetes","nextCursor":"ZVt07cGHkvI2wRk2CJf6_LLt25GeMN8wd7KrgP4Ymj2e"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Try it

Live request with your key

const data = await client.run(  "research:pubmed",  "abstract",  { id: "33301246,32109013" });

PubMed

NCBI E-utilities across 37 Entrez databases — literature search, summaries, full records, cross-database links, citation metrics and clinical trials.

22 endpoints163 calls21/22 passing

Get API key

efetch db=pubmed&rettype=abstract&retmode=text, pre-bound. The payload is one numbered block per record; the split keys each block back to its PMID so the

GET/v1/…pubmed/abstract

passing · 0.8s5m cache

Try it

Parameters

string · query · required

Comma-separated PMIDs, max 200 per call.

Example response

{"project":"research:pubmed",  "data": {"db":"pubmed","count":2,    "items": [      {"pmid":"33301246","content":"1. N Engl J Med. 2020 Dec 31;383(27):2603-2615. doi: 10.1056/NEJMoa2034577. Epub \n2020 Dec 10.\n\nSafety and Efficacy of the BNT162b2 mRNA Covid-19 Vaccine.\n\nPolack FP(1), Thomas SJ(…"      },      {"pmid":"32109013","content":"2. N Engl J Med. 2020 Apr 30;382(18):1708-1720. doi: 10.1056/NEJMoa2002032. Epub \n2020 Feb 28.\n\nClinical Characteristics of Coronavirus Disease 2019 in China.\n\nGuan WJ(1), Ni ZY(1)…"      }    ],"format":"text","provider":"pubmed"  },"timestamp":"2026-08-30T00:49:24Z"}

Errors

401Missing or invalid x-api-key
404Not found or private
429Rate limit or monthly quota reached

Code

const data = await client.run(  "research:pubmed",  "abstract",  { id: "33301246,32109013" });