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OpenAPI Specification

openapi: 3.2.0
info:
  title: Fourzerotwo Si Calculators API
  version: 1.1.0
  contact:
    url: https://fourzerotwo.si
  description: 'Operations tagged calculators across 2 of this provider''s published API definitions: openapi.json, fourzerotwo-si-openapi.json. Each path carries the servers of the definition it was published in.'
servers:
- url: https://fourzerotwo.si
tags:
- name: calculators
  description: 'Calculators: Currency conversion at ECB reference rates, UK business-day maths with official bank holidays, and postcode-to-postcode distance.'
paths:
  /v1/calculators/uk-business-days:
    get:
      operationId: calculators__uk_business_days
      summary: 'Calculators: UK business days'
      description: 'Is a date a UK business day; add or subtract N business days; count business days between dates. Uses official bank holidays per nation. Price: $0.001 USDC per call via x402. Free within the daily allowance with a free key.'
      tags:
      - calculators
      externalDocs:
        url: https://fourzerotwo.si/apis/calculators/uk-business-days
      parameters:
      - name: date
        in: query
        required: true
        description: YYYY-MM-DD
        schema:
          type: string
        example: '2026-12-23'
      - name: add
        in: query
        required: false
        description: Business days to add (negative to subtract)
        schema:
          type: integer
        example: 5
      - name: until
        in: query
        required: false
        description: Count business days until YYYY-MM-DD
        schema:
          type: string
        example: '2027-01-08'
      - name: nation
        in: query
        required: false
        description: england-and-wales, scotland, northern-ireland
        schema:
          type: string
        example: england-and-wales
      responses:
        '200':
          description: The data (paid, or free tier).
          content:
            application/json: {}
        '402':
          $ref: '#/components/responses/PaymentRequired'
        '400':
          $ref: '#/components/responses/Error'
        '404':
          $ref: '#/components/responses/Error'
        '502':
          $ref: '#/components/responses/Error'
      security:
      - {}
      - freeKey: []
      x-price-usd: '0.001000'
      x-free-tier: free
      x-mcp-tool: calculators__uk-business-days
    servers:
    - url: https://fourzerotwo.si
  /v1/calculators/postcode-distance:
    get:
      operationId: calculators__postcode_distance
      summary: 'Calculators: Distance between postcodes'
      description: 'Straight-line distance (km and miles) and compass bearing between two UK postcodes. Price: $0.002 USDC per call via x402. Free within the daily allowance with a free key.'
      tags:
      - calculators
      externalDocs:
        url: https://fourzerotwo.si/apis/calculators/postcode-distance
      parameters:
      - name: from
        in: query
        required: true
        description: Postcode
        schema:
          type: string
        example: SW1A 1AA
      - name: to
        in: query
        required: true
        description: Postcode
        schema:
          type: string
        example: CT9 1JD
      responses:
        '200':
          description: The data (paid, or free tier).
          content:
            application/json: {}
        '402':
          $ref: '#/components/responses/PaymentRequired'
        '400':
          $ref: '#/components/responses/Error'
        '404':
          $ref: '#/components/responses/Error'
        '502':
          $ref: '#/components/responses/Error'
      security:
      - {}
      - freeKey: []
      x-price-usd: '0.002000'
      x-free-tier: free
      x-mcp-tool: calculators__postcode-distance
    servers:
    - url: https://fourzerotwo.si
  /v1/calculators/currency-convert:
    get:
      operationId: calculators__currency_convert
      summary: 'Calculators: Currency conversion'
      description: 'Convert between ~30 currencies at the ECB reference rate for today or any date in the last 90 days. Price: $0.001 USDC per call via x402. Free within the daily allowance with a free key.'
      tags:
      - calculators
      externalDocs:
        url: https://fourzerotwo.si/apis/calculators/currency-convert
      parameters:
      - name: from
        in: query
        required: true
        description: ISO currency
        schema:
          type: string
          maxLength: 3
        example: GBP
      - name: to
        in: query
        required: true
        description: ISO currency
        schema:
          type: string
          maxLength: 3
        example: USD
      - name: amount
        in: query
        required: false
        description: Amount (default 1)
        schema:
          type: string
        example: '250'
      - name: date
        in: query
        required: false
        description: YYYY-MM-DD (default latest)
        schema:
          type: string
      responses:
        '200':
          description: The data (paid, or free tier).
          content:
            application/json: {}
        '402':
          $ref: '#/components/responses/PaymentRequired'
        '400':
          $ref: '#/components/responses/Error'
        '404':
          $ref: '#/components/responses/Error'
        '502':
          $ref: '#/components/responses/Error'
      security:
      - {}
      - freeKey: []
      x-price-usd: '0.001000'
      x-free-tier: free
      x-mcp-tool: calculators__currency-convert
    servers:
    - url: https://fourzerotwo.si
components:
  responses:
    PaymentRequired:
      description: x402 payment required. The body (also base64 in the PAYMENT-REQUIRED header) lists accepted payments.
      headers:
        PAYMENT-REQUIRED:
          schema:
            type: string
          description: Base64 JSON x402 v2 PaymentRequired
      content:
        application/json:
          schema:
            type: object
            properties:
              x402Version:
                type: integer
              error:
                type: string
              accepts:
                type: array
                items:
                  type: object
    Error:
      description: 400 = invalid input, 404 = not found at the source, 502 = the source failed. Never charged.
      content:
        application/json:
          schema:
            type: object
            properties:
              error:
                type: string
              charged:
                type: boolean
  securitySchemes:
    freeKey:
      type: apiKey
      in: header
      name: X-API-Key
      description: Optional free key (fzt_…) for the free tier.
x-refined-from:
- openapi.json
- fourzerotwo-si-openapi.json