openapi: 3.2.0
info:
  title: NCBI E-Utilities Link API
  description: The NCBI E-Utilities (Entrez Programming Utilities) are the public API to the NCBI Entrez system providing access to all 41 Entrez databases including PubMed (biomedical literature), PMC (full-text articles), Gene, Nuccore (nucleotide sequences), Protein, SNP, and more. Supports search, retrieval, linking, posting, and spelling operations. API keys from https://www.ncbi.nlm.nih.gov/account/ increase the rate limit from 3 to 10 requests per second.
  version: 1.0.0
  contact:
    name: NCBI
    url: https://www.ncbi.nlm.nih.gov/home/develop/api/
    email: info@ncbi.nlm.nih.gov
  license:
    name: Public Domain
    url: https://www.usa.gov/government-works
servers:
- url: https://eutils.ncbi.nlm.nih.gov/entrez/eutils
  description: NCBI E-Utilities API
tags:
- name: Link
  description: Find linked records across databases
paths:
  /elink.fcgi:
    get:
      operationId: getLinkages
      summary: Get Linked Records
      description: Find records related to a set of input UIDs in any Entrez database. Supports finding related articles, linked sequences, gene-to-protein links, and other cross-database connections.
      tags:
      - Link
      parameters:
      - name: dbfrom
        in: query
        description: Source database
        required: true
        schema:
          type: string
        example: pubmed
      - name: db
        in: query
        description: Target database (leave empty for related records in same db)
        required: false
        schema:
          type: string
      - name: id
        in: query
        description: Comma-separated source UIDs
        required: true
        schema:
          type: string
        example: '33515491'
      - name: api_key
        in: query
        required: false
        schema:
          type: string
      - name: cmd
        in: query
        description: Link command (neighbor, prlinks, llinks, acheck, ncheck, lcheck)
        required: false
        schema:
          type: string
          default: neighbor
      - name: linkname
        in: query
        description: Named link to follow (e.g. pubmed_pubmed_citedin)
        required: false
        schema:
          type: string
      - name: retmode
        in: query
        required: false
        schema:
          type: string
          default: json
      responses:
        '200':
          description: Linked record UIDs and link names
          content:
            application/json:
              schema:
                type: object
components:
  securitySchemes:
    ApiKeyAuth:
      type: apiKey
      in: query
      name: api_key
      description: NCBI API key from https://www.ncbi.nlm.nih.gov/account/