openapi: 3.2.0
info:
  title: ATF eRegulations Diffs API
  version: '2026-09-05'
  summary: Read-only JSON API over ATF's eRegulations platform (27 CFR Parts 447, 478, 479, 555, 646, 771).
  description: Machine-readable description of the public JSON API served at https://regulations.atf.gov/api/.
  contact:
    name: Bureau of Alcohol, Tobacco, Firearms and Explosives
    url: https://www.atf.gov/contact
  license:
    name: U.S. Government Work (17 U.S.C. 105)
    url: https://www.usa.gov/government-works
servers:
- url: https://regulations.atf.gov/api
  description: ATF eRegulations production API (anonymous, no key)
tags:
- name: Diffs
  description: Structural differences between two versions of a part.
paths:
  /diff/{part}/{older}/{newer}:
    get:
      operationId: getVersionDiff
      tags:
      - Diffs
      summary: Difference between two versions of a CFR part
      description: Returns a node-keyed map of changes. An empty object means the platform holds no computed diff between the two versions requested.
      parameters:
      - $ref: '#/components/parameters/Part'
      - name: older
        in: path
        required: true
        schema:
          type: string
          examples:
          - 2025-04872
      - name: newer
        in: path
        required: true
        schema:
          type: string
          examples:
          - 2026-01141
      responses:
        '200':
          description: Diff map, keyed by node label string
          content:
            application/json:
              schema:
                type: object
                additionalProperties: true
components:
  parameters:
    Part:
      name: part
      in: path
      required: true
      description: CFR part number. eRegulations carries 447, 478, 479, 555, 646 and 771.
      schema:
        type: string
        enum:
        - '447'
        - '478'
        - '479'
        - '555'
        - '646'
        - '771'
x-generated-from: live probe of https://regulations.atf.gov/api/* on 2026-09-05
x-api-evangelist-modeled: true
x-upstream-project: https://github.com/atfweb/regulations-core