> ## Documentation Index
> Fetch the complete documentation index at: https://docs.symmetry.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Licensing

> How STE licensing and authentication work across the hosted API, on-premise SDK, and AI interfaces.

Access to the Symmetry Tax Engine is licensed by Symmetry. How your license is delivered — and how you authenticate — depends on which interface you use.

## How you authenticate

Each interface uses one of three credentials. Use this table to find the one you need, then see [the credentials](#the-credentials) below for details.

| Interface      | Credential                    | Notes                                      |
| -------------- | ----------------------------- | ------------------------------------------ |
| Hosted API     | API key                       | Separate staging and production keys       |
| Tax Logic API  | API key                       | Same key model as the hosted API           |
| On-premise SDK | STE license file + API key\*  | Bundled with your licensed distribution    |
| STE MCP        | Client Support Center sign-in | Symmetry hosts the licensed engine for you |
| Tax Logic Chat | Client Support Center sign-in | You sign in as yourself                    |

*\* On-premise installs also use an API key for the [Symmetry Location Service](#location-data-and-the-symmetry-location-service) (address geocoding), separate from the STE license file.*

<Note>
  For the hosted API and the hosted STE MCP, Symmetry runs the licensed engine on your behalf — you don't manage a license file yourself.
</Note>

## The credentials

<CardGroup cols={3}>
  <Card title="STE license file" icon="file-contract">
    Authorizes the engine for an on-premise install; it's part of the licensed distribution.
  </Card>

  <Card title="API key" icon="key">
    A per-client/product key issued by Symmetry, sent as the raw value of the `Authorization` header on every request.
  </Card>

  <Card title="Client Support Center credentials" icon="user">
    User-level sign-in — you authenticate as yourself, not with a shared service key.
  </Card>
</CardGroup>

## Hosted API

The STE Hosted API is accessed with an **API key**, included as an `Authorization` header on every request. You receive your keys when you sign, one per environment:

| Environment    | Purpose                   |
| -------------- | ------------------------- |
| **Staging**    | Development and testing   |
| **Production** | Live payroll calculations |

<Warning>
  Use your staging API key only against the staging environment, and your production API key only against the production environment. Mixing them will cause your requests to fail.
</Warning>

<Info>
  Unsure of your API key? [Open a support ticket](https://support.symmetry.com/hc/en-us/requests/new) and Symmetry's Client Success team can help.
</Info>

## On-premise SDK

The on-premise SDK is licensed with a **license file** named `ste-license.dat`, which you download from Symmetry's [Download Center](https://client-downloads.symmetry.com/saml) (as a ZIP file with "License" in the name). Place `ste-license.dat` in your STE directory — the root of your installation. Alternatively, set the `STE_LICENSE_KEY` environment variable to the file's contents; the engine checks that variable first.

<Warning>
  You must always include the license file as part of your distribution or installation. **The Symmetry Tax Engine will not function without a valid license file.**
</Warning>

## Location data and the Symmetry Location Service

Full street-address and geocoordinate geocoding uses the [**Symmetry Location Service (SLS)**](/ste/location-service/overview).

On the hosted API, SLS is handled for you. On an on-premise install, you set an `SLS_API_KEY` in `ste.conf` — a configuration detail, not a separate license.

## Related

<CardGroup cols={2}>
  <Card title="Hosted API vs. on-premise SDK" icon="scale-balanced" href="/ste/overview/hosted-vs-on-premise">
    Decide which delivery model fits your needs.
  </Card>

  <Card title="Hosted API quickstart" icon="cloud" href="/ste/quickstarts/hosted-api-quickstart">
    Make your first authenticated request.
  </Card>

  <Card title="AI interfaces" icon="robot" href="/ste/ai-interfaces/overview">
    Set up the STE MCP, Tax Logic Chat, and Tax Logic API.
  </Card>
</CardGroup>