vocabulary:
  - term: base_code
    definition: >
      The ISO 4217 three-letter currency code used as the reference currency for exchange
      rate calculations. All rates in the response are expressed as units of the target
      currency per one unit of the base currency.
    type: field
    example: USD

  - term: target_code
    definition: >
      The ISO 4217 three-letter currency code for the destination currency in a pair
      conversion request.
    type: field
    example: GBP

  - term: conversion_rates
    definition: >
      A JSON object mapping ISO 4217 currency codes to their exchange rate values
      relative to the base currency. Each value represents how many units of that
      currency equal one unit of the base currency.
    type: field

  - term: conversion_rate
    definition: >
      The exchange rate from a base currency to a target currency in a pair conversion
      response. Expressed as units of target currency per one unit of base currency.
    type: field
    example: 0.8412

  - term: conversion_result
    definition: >
      The result of multiplying the requested amount by the conversion_rate. Returned
      only when an amount is specified in a pair conversion request.
    type: field
    example: 5.8884

  - term: supported_codes
    definition: >
      An array of two-element arrays, each containing an ISO 4217 currency code and
      the full English name of that currency. Lists all 165 currencies supported by
      the API.
    type: field

  - term: time_last_update_unix
    definition: >
      Unix epoch timestamp (seconds since January 1, 1970 UTC) indicating when the
      current set of exchange rates was last updated.
    type: field
    example: 1585267200

  - term: time_last_update_utc
    definition: >
      Human-readable UTC datetime string indicating when the exchange rates were last
      updated.
    type: field
    example: "Fri, 27 Mar 2020 00:00:00 +0000"

  - term: time_next_update_unix
    definition: >
      Unix epoch timestamp indicating when the exchange rates will next be updated,
      depending on the subscription plan (daily, hourly, or every 5 minutes).
    type: field

  - term: time_next_update_utc
    definition: >
      Human-readable UTC datetime string indicating when the next exchange rate update
      will occur.
    type: field

  - term: plan_quota
    definition: >
      The total number of API requests allowed per billing period under the current
      subscription plan. The free tier provides 1,500 requests per month.
    type: field
    example: 1500

  - term: requests_remaining
    definition: >
      The number of API requests that can still be made within the current billing period
      before the quota is reached.
    type: field
    example: 1243

  - term: refresh_day_of_month
    definition: >
      The day of the month (1–31) on which the request quota resets for the current
      billing period.
    type: field
    example: 1

  - term: result
    definition: >
      A field present in all API responses indicating whether the request was successful
      ("success") or failed ("error").
    type: field
    values:
      - success
      - error

  - term: error-type
    definition: >
      A machine-readable string returned in error responses that identifies the specific
      reason the request failed.
    type: field
    values:
      - unsupported-code: The provided currency code is not supported
      - malformed-request: The request URL structure is invalid
      - invalid-key: The API key is not recognized
      - inactive-account: The email address associated with the account has not been confirmed
      - quota-reached: The monthly request quota for the plan has been exhausted

  - term: ISO 4217
    definition: >
      The international standard defining three-letter codes for world currencies
      (e.g. USD for US Dollar, EUR for Euro, GBP for British Pound Sterling). All
      currency codes used by ExchangeRate-API follow this standard.
    type: concept

  - term: exchange rate
    definition: >
      The value of one currency expressed in terms of another currency. For example,
      an exchange rate of 0.84 for EUR/GBP means 1 Euro buys 0.84 British Pounds.
    type: concept

  - term: base currency
    definition: >
      The reference or starting currency in an exchange rate calculation. Exchange rates
      for all other currencies are expressed relative to one unit of the base currency.
    type: concept

  - term: pair conversion
    definition: >
      A currency exchange operation involving exactly two currencies (a base and a target).
      The pair conversion endpoint provides a focused response with only the rate between
      those two currencies rather than all 165 supported currencies.
    type: concept

  - term: historical data
    definition: >
      Exchange rates recorded on past dates. ExchangeRate-API provides historical data
      back to January 1, 1990. Access to historical data requires a paid subscription plan.
    type: concept

  - term: quota
    definition: >
      The maximum number of API requests allowed per billing period. Quotas vary by
      subscription plan, from 1,500 per month on the free tier to higher limits on
      paid plans.
    type: concept

  - term: API key
    definition: >
      A unique alphanumeric token assigned to each account that authenticates API
      requests. Can be passed either embedded in the URL path or as a Bearer token
      in the Authorization HTTP header.
    type: concept