Columbia University Locations API

openapi: 3.2.0
info:
  title: Columbia University Libraries Hours Locations API
  version: 1.0.0
  summary: Opening hours and open-now status for Columbia University Libraries locations.
  description: 'The public read API behind Columbia University Libraries'' hours service. It answers two questions without authentication: which library locations are open right now, and what the posted hours are for one location over a date or a date range. It is operated by Columbia University Libraries on Columbia''s own infrastructure — hours.library.columbia.edu resolves to diglib-rails-prod1.cul.columbia.edu (128.59.222.118) and is served under a TLS certificate issued to O=Columbia University by the InCommon/Internet2 CA. The application is Columbia''s own Rails codebase, published openly at github.com/cul/ldpd-hours under the cul GitHub organisation.


    This is the only institution-operated, publicly consumable, unauthenticated API surface found anywhere in Columbia University''s estate. It is small, and it is genuinely theirs.


    Columbia publishes no OpenAPI, no rate-limit policy, no terms of use and no changelog for this API. This document is a description of observed behaviour, not a contract Columbia has committed to.'
  contact:
    name: Columbia University Libraries
    url: https://library.columbia.edu/services/askalibrarian.html
  x-provenance:
    generated: '2026-08-19'
    method: probed
    source: https://hours.library.columbia.edu/api/v1/locations/open_now
    source_code: https://github.com/cul/ldpd-hours
    x-operator: institution
    x-operator-evidence: hours.library.columbia.edu -> diglib-rails-prod1.cul.columbia.edu -> 128.59.222.118 (Columbia University address space); TLS subject C=US, ST=New York, O=Columbia University, CN=library.columbia.edu; issuer C=US, O=Internet2, CN=InCommon RSA Server CA 2.
servers:
- url: https://hours.library.columbia.edu/api/v1
  description: Production. The only published deployment.
security: []
tags:
- name: Locations
  description: Library locations and their posted opening hours.
paths:
  /locations/open_now:
    get:
      operationId: getLocationsOpenNow
      tags:
      - Locations
      summary: List the library locations that are open at this moment
      description: Returns every Columbia University Libraries location whose current timetable entry is open at request time, keyed by location code. Locations flagged closed or TBD are excluded, and a sub-location is suppressed when its primary location is already open. When no location is open the `data` member is null rather than an empty object — a caller must handle both shapes.
      security: []
      responses:
        '200':
          description: A map of open location codes to their current opening window. `data` is null when nothing is open.
          headers:
            Access-Control-Allow-Origin:
              description: Always `*`; the API is browser-callable cross-origin.
              schema:
                type: string
            Cache-Control:
              description: Observed as `max-age=0, private, must-revalidate` — the service asks not to be cached.
              schema:
                type: string
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/OpenNowResponse'
              examples:
                sevenLocationsOpen:
                  summary: Observed response, 2026-08-19
                  externalValue: ../examples/columbia-library-hours-open-now-example.json
  /locations/{code}:
    get:
      operationId: getLocationHours
      tags:
      - Locations
      summary: Get posted hours for one location, for a date or a date range
      description: Returns the posted opening hours for a single location. Exactly one of `date` or the `start_date`+`end_date` pair must be supplied; `date` accepts the literal `today`. If no date parameter is supplied the request does not reach this operation at all — the Rails router falls through and an HTML page is returned instead of JSON, which is a real defect in the deployed service and is recorded in errors/columbia-errors.yml.
      security: []
      parameters:
      - name: code
        in: path
        required: true
        description: The location's short code, as returned by /locations/open_now. Observed codes include butler, butler-24, barnard, law, law-reference, social-work and lio.
        schema:
          type: string
          examples:
          - butler
      - name: date
        in: query
        required: false
        description: A single ISO-8601 date, or the literal string `today`.
        schema:
          type: string
          examples:
          - today
          - '2026-08-19'
      - name: start_date
        in: query
        required: false
        description: First date of an inclusive range. Must be supplied with `end_date`.
        schema:
          type: string
          format: date
      - name: end_date
        in: query
        required: false
        description: Last date of an inclusive range. Must be supplied with `start_date` and must not be earlier than it, or the service answers 400.
        schema:
          type: string
          format: date
      responses:
        '200':
          description: Posted hours for the requested location across the requested dates.
          headers:
            Access-Control-Allow-Origin:
              schema:
                type: string
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/LocationHoursResponse'
              examples:
                singleDay:
                  summary: Observed response for butler?date=today
                  externalValue: ../examples/columbia-library-hours-location-day-example.json
                dateRange:
                  summary: Observed response for a three-day range
                  externalValue: ../examples/columbia-library-hours-location-range-example.json
        '400':
          description: 'An unparseable date, or a start_date later than end_date. Observed body `{"error":{"msg":"400: invalid date"},"data":null}`.'
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
              examples:
                invalidDate:
                  externalValue: ../examples/columbia-library-hours-error-400-example.json
        '404':
          description: 'No location exists with the supplied code. Observed body `{"error":{"msg":"404: location not found"},"data":null}`.'
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/ErrorResponse'
              examples:
                unknownLocation:
                  externalValue: ../examples/columbia-library-hours-error-404-example.json
components:
  schemas:
    OpenWindow:
      type: object
      required:
      - open_time
      - close_time
      - formatted_date
      properties:
        open_time:
          type: string
          pattern: ^[0-2][0-9]:[0-5][0-9]$
          description: Local opening time, 24-hour HH:MM. America/New_York; the API states no timezone.
          examples:
          - 09:00
        close_time:
          type: string
          pattern: ^[0-2][0-9]:[0-5][0-9]$
          description: Local closing time, 24-hour HH:MM.
          examples:
          - '21:00'
        formatted_date:
          type: string
          description: Human display string. Named `formatted_date` but carries a time, not a date.
          examples:
          - Until 09:00PM
    ErrorResponse:
      type: object
      required:
      - error
      - data
      properties:
        error:
          type: object
          required:
          - msg
          properties:
            msg:
              type: string
              description: Human-readable message. Carries the HTTP status as a text prefix rather than a machine-readable code; there is no error identifier an agent can branch on.
              examples:
              - '404: location not found'
        data:
          type: 'null'
    LocationHoursResponse:
      type: object
      required:
      - data
      properties:
        data:
          type: object
          description: Single-key map of the requested location code to its list of daily entries.
          additionalProperties:
            type: array
            items:
              $ref: '#/components/schemas/DayHours'
    DayHours:
      type: object
      required:
      - date
      - closed
      - tbd
      - formatted_date
      properties:
        date:
          type: string
          format: date
          examples:
          - '2026-08-19'
        open_time:
          type:
          - string
          - 'null'
          pattern: ^[0-2][0-9]:[0-5][0-9]$
          description: Absent or null when the location is closed or its hours are TBD.
        close_time:
          type:
          - string
          - 'null'
          pattern: ^[0-2][0-9]:[0-5][0-9]$
        closed:
          type: boolean
          description: True when the location is posted as closed for that date.
        tbd:
          type: boolean
          description: True when hours for that date have not yet been decided.
        note:
          type:
          - string
          - 'null'
          description: Free-text note on the day, e.g. the academic period.
          examples:
          - Intersession
        short_note:
          type:
          - string
          - 'null'
        short_note_url:
          type:
          - string
          - 'null'
          description: Link accompanying short_note. Empty string when unset, not null.
        formatted_date:
          type: string
          description: Human display string for the day's window.
          examples:
          - 09:00AM-09:00PM
    OpenNowResponse:
      type: object
      required:
      - data
      properties:
        data:
          description: Map of location code to the current opening window, or null when no location is open.
          oneOf:
          - type: 'null'
          - type: object
            additionalProperties:
              $ref: '#/components/schemas/OpenWindow'