> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://developer.fortresstech.io/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://developer.fortresstech.io/_mcp/server.

# ILS Unit Availability

## Overview

Fortress provides a dedicated API endpoint for Internet Listing Services (ILS) to retrieve unit availability in real-time, following the MITS 4.1 XML standard. This documentation explains how the integration works, what to expect in the response, and how to get started.

> **Note**
>
> While the ILS endpoint provides real-time data, we recommend defining a polling interval during onboarding. This helps avoid issues with throttling and rate limits, and ensures reliable access to unit availability information.

## How Unit Availability Works

The ILS integration allows vendors (such as apartment listing services) to programmatically request up-to-date unit availability from Fortress. The process is as follows:

1. **Vendor** sends a request to the Fortress ILS endpoint.
2. **Fortress** authenticates and processes the request, gathering the latest unit data.
3. **Fortress** returns a response in MITS 4.1 XML format, containing available units, floorplans, and property details.

### Sequence Diagram

```mermaid
sequenceDiagram
    participant Vendor
    participant Fortress
    Vendor->>Fortress: GET /ils/units (with API key & auth)
    Fortress-->>Vendor: Validate request & auth
    Fortress->>Fortress: Fetch unit availability data
    Fortress-->>Vendor: Return MITS 4.1 XML response
```

## API Endpoint

| Action                | Endpoint     | Method | Response                 |
| --------------------- | ------------ | :----: | ------------------------ |
| Get Unit Availability | `/ils/units` |   GET  | XML (MITS 4.1 compliant) |

#### Base URL

`https://api-prod.fortresstech.io`

#### Request Parameters

| Parameter        | Type   | Description                       | Required | Default |
| ---------------- | ------ | --------------------------------- | -------- | ------- |
| `format`         | string | Response format (`json` or `xml`) | No       | `json`  |
| `organizationId` | string | Filter by organization            | No       |         |

#### Example Request (cURL)

```bash
curl --location --request GET 'https://api-prod.fortresstech.io/ils/units?format=xml' \
--header 'x-api-key: {api-key}'
```

## Authentication & Onboarding

* Requires a dedicated ILS API key and `x-api-key` header.
* The ILS integration can be configured to provide organization-wide information or information per property. This is determined during initial onboarding with the help of a Fortress customer success representative.

> **Note**
>
> Use your ILS API key for this integration. This key is separate from standard Fortress API keys.

## Response Structure

* The response is a MITS 4.1 XML manifest containing unit availability, property, and floorplan details.
* See the [Response Model](/ils-integration/unit-availability/response-model) for a detailed breakdown.

## Why ILS for Unit Availability?

* **Standardized:** Matches MITS 4.1, widely adopted by ILS platforms.
* **Easy Integration:** Designed for quick onboarding by ILS partners.

## Getting Started

1. Contact Fortress to begin onboarding and receive your dedicated ILS API key.
2. Make a GET request to the endpoint with required headers.
3. Parse the XML response according to the MITS 4.1 schema.

---

This section is a starting point for anyone interested in consuming Fortress unit availability for ILS services.