openapi: 3.2.0
info:
  title: Chessigma Public Elo Calculator API
  version: 1.0.0
  description: 'Free, no-auth API for the Chessigma chess analysis platform. Submit games (PGN) for analysis, read analysis results, compute Elo rating changes, and fetch the daily puzzle. Chess engine analysis runs client-side in the browser (Stockfish WebAssembly), so this API is compute-free: GET /game/{gameId} returns analysis only after a user has opened the game page and triggered it. No signup, no API key, no paywall. Global rate limit: 30 requests/minute across all callers.'
  contact:
    name: Chessigma
    url: https://www.chessigma.com/developers
  license:
    name: Terms of Service
    url: https://www.chessigma.com/tos
servers:
- url: https://www.chessigma.com/public-api/v1
  description: Production
security: []
tags:
- name: Elo Calculator
paths:
  /elo-calculator:
    get:
      operationId: calculateElo
      summary: Compute an Elo rating change for a single game
      description: Pure arithmetic. Returns the new rating, point change, and expected score.
      parameters:
      - name: yourRating
        in: query
        required: true
        schema:
          type: integer
          minimum: 100
          maximum: 4000
        example: 1500
      - name: opponentRating
        in: query
        required: true
        schema:
          type: integer
          minimum: 100
          maximum: 4000
        example: 1400
      - name: result
        in: query
        required: true
        schema:
          type: string
          enum:
          - win
          - draw
          - loss
        example: win
      - name: system
        in: query
        required: false
        schema:
          type: string
          enum:
          - fide
          - chesscom
          - lichess
          default: fide
      - name: kFactor
        in: query
        required: false
        description: Override the default K-factor for the chosen system.
        schema:
          type: integer
          minimum: 1
          maximum: 100
      responses:
        '200':
          description: Computed rating change
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/EloResponse'
              example:
                yourRating: 1500
                opponentRating: 1400
                result: win
                system: fide
                kFactor: 20
                expectedScore: 0.6401
                newRating: 1507
                change: 7
        '400':
          description: Invalid query parameters
          content:
            application/json:
              schema:
                $ref: '#/components/schemas/Error'
        '429':
          description: Rate limit exceeded
      tags:
      - Elo Calculator
components:
  schemas:
    Error:
      type: object
      properties:
        error:
          type: string
        details:
          description: Optional validation detail.
      required:
      - error
    EloResponse:
      type: object
      properties:
        yourRating:
          type: integer
        opponentRating:
          type: integer
        result:
          type: string
          enum:
          - win
          - draw
          - loss
        system:
          type: string
          enum:
          - fide
          - chesscom
          - lichess
        kFactor:
          type: integer
        expectedScore:
          type: number
          description: Probability of scoring (0–1).
        newRating:
          type: integer
        change:
          type: integer