# Concepts [#concepts]

Use this section when you need a mental model before choosing an API, writing
input values or reviewing calculator output.

## Pages [#pages]

* [Calculators](/concepts/calculators)
* [Facts](/concepts/facts)
* [Rules](/concepts/rules)
* [Jurisdictions and tax years](/concepts/jurisdictions-and-tax-years)
* [Money and branded values](/concepts/money-and-branded-values)
* [Reports](/concepts/reports)
* [Diagnostics](/concepts/diagnostics)
* [SDK, HTTP API and calculators service boundary](/concepts/sdk-http-api-and-calculators-service-boundary)

## Related sections [#related-sections]

* [SDK](/sdk)
* [Guides](/guides)
* [Contributing](/contributing)