The User Interface (UI) API is specifically designed for building native mobile applications and custom web applications that require the look and feel of the Salesforce Lightning Experience. It is the only API that provides both data and the necessary metadata (such as layouts, themes, and field-level details) in a single, streamlined response. This allows the custom UI to automatically adapt to administrative changes made within the Salesforce org, ensuring a consistent user experience without requiring code changes in the mobile app.

1. Salesforce Developer Documentation

User Interface API Developer Guide

"Get Started with User Interface API": "User Interface API is the API for building Salesforce UI. To build a Salesforce-like UI

you need more than data—you need metadata... UI API gives you data and metadata in a single response. It’s the key to building a native mobile app or a custom web app that feels like the Salesforce you know and love."

2. Salesforce Developer Documentation

"Which API Should I Use?": This guide explicitly recommends the UI API for the use case: "Build a native mobile app or a custom web app that has the Salesforce look and feel." It contrasts this with the REST API

which is recommended for general data integration.

3. Salesforce Developer Documentation

REST API Developer Guide

"Introduction": The guide defines the REST API's purpose as providing "a powerful

convenient

and simple REST-based web services interface for interacting with Salesforce." This interaction is focused on data records

not UI metadata.

4. Salesforce Developer Documentation

Streaming API Developer Guide

"Streaming API": This document states

"Use Streaming API to receive notifications for changes to Salesforce data that match a SOQL query you define." This confirms its purpose is event-based

not UI construction.