Custom Application for React UI Bundles

Create and configure a Salesforce Custom Application that hosts a React UI bundle in Lightning Experience. This skill generates the CustomApplication metadata so the app appears in the Lightning App Launcher and can be accessed by internal users.

Custom Applications differ from Experience Sites: they don't need Networks, CustomSite, DigitalExperienceConfig, or DigitalExperienceBundle metadata. The Custom Application acts as a thin launcher entry that delegates rendering to the React UI bundle referenced by uiBundle.

Required Properties

Resolve all properties before generating any metadata. Each has a fallback chain — work through each option in order until a value is found.

The appNamespace and appName connect the Custom Application to the correct React UI bundle. In newer API versions this uses <uiBundle>{appNamespace}__{appName}</uiBundle>; in older versions it uses <webApplication>{appName}</webApplication>. Getting this wrong means the app launcher entry exists but shows a blank page. Step 2 of the workflow determines which field to use.

Generation Workflow

Step 1: Resolve All Required Properties

Determine values for all properties before constructing anything. Use the resolution strategies in the table above.

Step 2: Query API Context (Version-Aware Field Discovery)

Call salesforce-api-context MCP tools to discover which fields exist for the target org's API version. This ensures the generated metadata is compatible with the user's Salesforce version.

Required calls — use the metadataType parameter exactly as shown. Do not substitute a detail parameter or any other shape; metadataType is the only parameter this tool accepts:

1. get_metadata_type_fields({ "metadataType": "CustomApplication" }) — check whether the uiBundle field exists in the response's field list
2. get_metadata_type_fields({ "metadataType": "UIBundle" }) — check whether the target field exists in the response's field list

Field resolution based on API response:

If salesforce-api-context is unavailable after a real attempt, fall back to the newer field names (uiBundle + target).

Step 3: Create the Project Structure

Create any files and directories that don't already exist:

Note: <sourceDir> is determined from sfdx-project.json. Read packageDirectories[] and use the entry where "default": true; the full source directory is <path>/main/default. If no default is set, use the first entry. Commonly force-app/main/default, but this path is configurable.

Step 4: Populate All Metadata Fields

Use the default template in the doc below. Values in {braces} are resolved property references — substitute them with the actual values from Step 1. Apply the field resolution from Step 2 to determine which XML elements to use.

Execution Note for Step 4: Load and use the doc

• Agents MUST read the full contents of the references/*.md file referenced in Step 4 before attempting to populate metadata fields.
• Read the file in full, replace placeholders (e.g. {appName}) with the resolved values, then use the expanded template to populate the metadata XML content.
• If Step 2 determined the older field names apply, substitute <uiBundle> with <webApplication> in the generated output.

Step 5: Update UI Bundle Meta XML

This step edits an existing file — it never creates a new one. UIBundle is a bundle-style metadata type: its meta XML normally lives inside its own folder at uiBundles/{appName}/{appName}.uibundle-meta.xml, alongside the bundle's other source files (e.g. index.html, src/). Some older or hand-authored projects may instead have it at the flat path uiBundles/{appName}.uibundle-meta.xml (no subfolder).

Run node scripts/resolve-uibundle-path.mjs "{appName}" — it prints the path of the existing meta XML (preferring the nested layout, falling back to the flat layout). Always invoke via node (never as a bare executable) so this works on Windows as well as macOS/Linux. Edit that exact file in place; do not create a second file at the other path or migrate it to a different layout as part of this skill.

If Step 2 confirmed the target field exists on UIBundle, add <target>CustomApplication</target> inside the existing <UIBundle> element of that file, preserving every other existing element and value untouched (skip this step entirely if the field doesn't exist in the org's API version — do not create the file or add <target> in that case).

Do NOT:

• Create a new .uibundle-meta.xml file
• Create a second .uibundle-meta.xml file at a different path when one already exists (nested or flat) — edit the existing one in place, wherever it is
• Leave the original uiBundles/{appName}/{appName}.uibundle-meta.xml (or uiBundles/{appName}.uibundle-meta.xml, if that's the existing layout) unmodified while adding <target> somewhere else

The only files this skill produces or modifies are applications/{appName}.app-meta.xml (new) and the existing {appName}.uibundle-meta.xml (edited in place, only if <target> applies). Any other UI-bundle-related file appearing in the output is a bug.

Example of the fully updated file (at uiBundles/{appName}/{appName}.uibundle-meta.xml, or the flat path if that's the existing layout) — this illustrates the end state of the existing file, not a new file to create:

<?xml version="1.0" encoding="UTF-8"?>
<UIBundle xmlns="http://soap.sforce.com/2006/04/metadata">
    <masterLabel>{appName}</masterLabel>
    <description>A Salesforce UI Bundle.</description>
    <isActive>true</isActive>
    <version>1</version>
    <target>CustomApplication</target>
</UIBundle>

Step 6: Do Not Modify Non-Templated Properties

Do not modify any default property values for CustomApplication metadata that are not expressed as variables wrapped in {braces}.

Verification Checklist

Before deploying, confirm:

• All required properties are resolved
• API context was queried to determine available fields (Step 2)
• applications/{appName}.app-meta.xml exists with correct content
• The bundle reference field matches the org's API version (<uiBundle> or <webApplication>)
• If target field is supported: the existing {appName}.uibundle-meta.xml (nested at uiBundles/{appName}/, or flat at uiBundles/, whichever already existed) has <target>CustomApplication</target>
• No extra .uibundle-meta.xml file was created — exactly one {appName}.uibundle-meta.xml exists, at whichever path it already lived at
• Deployment validates successfully:

sf project deploy validate --metadata CustomApplication UIBundle --target-org ${usernameOrAlias}