# Aspire Type System

Term type: API contract

A portable contract that exposes Aspire's .NET hosting APIs to supported guest languages through generated SDKs.

Also known as: ATS

The Aspire Type System (ATS) describes the types and operations that can cross the boundary between Aspire's .NET host and a guest-language AppHost.

Integration authors mark their .NET APIs for export. Aspire scans that metadata and generates language-specific SDKs, allowing guest code to use hosting integrations without reimplementing their orchestration behavior.

ATS includes portable representations for values, callbacks, and handles to host-side objects. A guest SDK uses those contracts to communicate with the host.

ATS support for an **AppHost language** is separate from support for a **workload language**. Your services do not need an ATS SDK to be orchestrated by Aspire.

## Practical example

In a TypeScript AppHost, adding Redis calls a generated SDK method that invokes the exported hosting API in Aspire's .NET host.

## Learn more

- [Understand the Aspire Type System](https://aspire.dev/architecture/multi-language-architecture/#aspire-type-system)

- [Export integrations for guest languages](https://aspire.dev/extensibility/multi-language-integration-authoring/)

## Related terms

- [AppHost](https://aspire.dev/hub/glossary/apphost/)

- [Hosting integration](https://aspire.dev/hub/glossary/hosting-integration/)

- [Polyglot](https://aspire.dev/hub/glossary/polyglot/)