Adobe Express Add-on Development Skill

Expert knowledge and tooling for developing Adobe Express add-ons. This skill leverages the Adobe Express MCP server to provide accurate, up-to-date API references, documentation, and best practices.

When to Use This Skill

Use this skill when:

• Building add-ons for Adobe Express
• Creating or modifying document content (shapes, text, images, media)
• Implementing UI panels with Spectrum Web Components
• Setting up communication between iframe runtime and document sandbox
• Troubleshooting add-on development issues
• Understanding project structure and file organization
• Accessing API documentation for Express Document SDK or Add-on UI SDK
• Working with OAuth, client storage, or add-on permissions
• User mentions: "Adobe Express", "add-on", "express-document-sdk", "document sandbox", "iframe runtime", "Spectrum Web Components"

Prerequisites

• Adobe Express MCP Server must be configured in

  .vscode/mcp.json

  or IDE settings
• Node.js 18+ for local development
• Basic understanding of HTML, CSS, and JavaScript
• Adobe Express account for testing add-ons

Key Concepts

Two-Runtime Architecture

Adobe Express add-ons run in two separate environments:

1. Iframe Runtime

   • Runs your UI (HTML, CSS, JavaScript)
   • Has access to Add-on UI SDK (

     addOnUISdk

     )
   • Can use standard Web APIs and DOM
   • Handles user interactions, OAuth, file imports/exports

2. Document Sandbox (optional)

   • Runs document manipulation code
   • Has access to Express Document SDK (

     editor

     ,

     colorUtils

     ,

     constants

     , etc.)
   • Limited Web APIs for security
   • Creates/modifies shapes, text, images, audio, video

Communication: Use Document Sandbox SDK (

runtime.exposeApi()

runtime.apiProxy()

Import Patterns

Always follow these patterns:

// Iframe Runtime (index.html, index.js, ui/ folder)
import addOnUISdk from "https://express.adobe.com/static/add-on-sdk/sdk.js";

// Document Sandbox (code.js, sandbox/code.js)
import addOnSandboxSdk from "add-on-sdk-document-sandbox";
import { editor, colorUtils, constants, fonts, viewport } from "express-document-sdk";

Critical:

• Add-on UI SDK and Document Sandbox SDK are default imports (no curly braces)
• Express Document SDK uses named imports (with curly braces)
• All SDKs use singleton pattern - never create new instances

Step-by-Step Workflows

Workflow 1: Access API Documentation

When you need: API references, type definitions, or documentation for Adobe Express add-on development.

Steps:

1. Use

   mcp_adobe-express_get_relevant_documentations

   tool with your query
2. Review the returned documentation snippets
3. For TypeScript definitions, use

   mcp_adobe-express_get_typedefinitions

   with appropriate

   api_type

   :

   • express-document-sdk

     - Document manipulation APIs

   • add-on-sdk-document-sandbox

     - Communication between runtimes

   • iframe-ui

     - UI SDK and iframe runtime APIs

Example queries:

• "How to create text in Adobe Express"
• "Document sandbox communication APIs"
• "Add-on manifest configuration"
• "Spectrum Web Components usage in add-ons"

Workflow 2: Understand Project Structure

When you need: To organize files, understand folder structure, or set up a new add-on.

Key principles:

• UI code (HTML, CSS, JS) → Iframe runtime (

  src/index.html

  ,

  src/ui/

  )
• Document manipulation → Document sandbox (

  src/sandbox/code.js

  )
• Never mix: UI code cannot go in sandbox, sandbox code cannot access DOM

Typical structure:

my-addon/
├── src/
│   ├── index.html              # UI entry point
│   ├── manifest.json           # Add-on config
│   ├── ui/
│   │   ├── index.js           # UI logic
│   │   └── styles.css         # Styles
│   └── sandbox/
│       └── code.js            # Document manipulation
├── webpack.config.js           # Build config (if using build templates)
└── package.json

Manifest configuration:

• UI-only:

  "main": "index.html"

• With document sandbox: Add

  "documentSandbox": "code.js"

  (build) or

  "sandbox/code.js"

  (no-build)

Workflow 3: Create Document Content

When you need: To add shapes, text, images, audio, or video to Adobe Express documents.

Steps:

1. Ensure code runs in document sandbox (not iframe runtime)
2. Import necessary modules from

   express-document-sdk

3. Use

   editor

   singleton for document operations
4. Wrap operations in async functions

Common APIs:

// Text
import { editor, text } from "express-document-sdk";
const textNode = text.createText({content: "Hello", fontSize: 24});
editor.context.insertionParent.children.append(textNode);

// Shapes
import { editor, RectangleNode } from "express-document-sdk";
const rect = editor.createRectangle();
rect.width = 100;
rect.height = 50;

// Images
import addOnUISdk from "https://express.adobe.com/static/add-on-sdk/sdk.js";
const blob = await fetch(imageUrl).then(r => r.blob());
await addOnUISdk.app.document.addImage(blob);

// Audio (title is MANDATORY)
await addOnUISdk.app.document.addAudio(audioBlob, {
  title: "Audio Title"
});

// Video (title is OPTIONAL)
await addOnUISdk.app.document.addVideo(videoBlob, {
  title: "Video Title"
});

Workflow 4: Build Add-on UI with Spectrum

When you need: To create user interfaces that match Adobe Express design language.

Steps:

1. Use Spectrum Web Components
2. Import components in HTML or via npm
3. Follow UX Guidelines

Common components:

• <sp-button>

  - Buttons

• <sp-textfield>

  - Input fields

• <sp-dropdown>

  - Dropdowns

• <sp-divider>

  - Dividers

• <sp-progress-circle>

  - Loading indicators

Example:

<sp-theme theme="express" scale="medium" color="light">
  <sp-button variant="primary" onclick="handleClick()">
    Click Me
  </sp-button>
  <sp-textfield placeholder="Enter text..."></sp-textfield>
</sp-theme>

Workflow 5: Implement OAuth Authentication

When you need: To connect to cloud storage services (Dropbox, OneDrive, Google Drive) or authenticate users.

Quick start:

1. Read

   references/oauth-implementation.md

   for complete guide
2. Copy OAuthUtils.js from import-images-using-oauth sample
3. See

   references/code-samples.md

   → "import-images-using-oauth" for full example

Steps:

1. Configure OAuth provider (e.g., Dropbox Developer Console)

   • Create web application
   • Add redirect URIs:

     https://express.adobe.com/static/oauth-redirect.html

     AND

     https://new.express.adobe.com/static/oauth-redirect.html

   • Note Client ID

2. Update manifest.json:

{
  "permissions": {
    "oauth": ["www.dropbox.com", "login.microsoftonline.com"]
  }
}

3. Implement PKCE flow:

import addOnUISdk from "https://express.adobe.com/static/add-on-sdk/sdk.js";
// Import OAuthUtils helper (copy from sample)

// Generate PKCE challenge
const challenge = await oauthUtils.generateChallenge();

// Authorize with provider
const { id, code, redirectUri, result } = await addOnUISdk.app.oauth.authorize({
  authorizationUrl: "https://www.dropbox.com/oauth2/authorize",
  clientId: "YOUR_CLIENT_ID",
  scope: "files.content.read",
  codeChallenge: challenge.codeChallenge
});

// Exchange for access token
await oauthUtils.generateAccessToken({
  id, clientId: "YOUR_CLIENT_ID",
  codeVerifier: challenge.codeVerifier,
  code, tokenUrl: "https://api.dropboxapi.com/oauth2/token",
  redirectUri
});

// Get token (always valid - handles refresh)
const accessToken = await oauthUtils.getAccessToken(id);

4. Store tokens persistently:

await addOnUISdk.instance.clientStorage.setItem("oauth_token", accessToken);

Reference: See

references/oauth-implementation.md

Workflow 6: Implement Iframe ↔ Sandbox Communication

When you need: To pass data between UI and document manipulation code.

Pattern:

In Document Sandbox (code.js):

import addOnSandboxSdk from "add-on-sdk-document-sandbox";

const api = {
  async addTextToDocument(text) {
    // Document manipulation logic
  }
};

addOnSandboxSdk.instance.runtime.exposeApi(api);

In Iframe Runtime (index.js):

import addOnUISdk from "https://express.adobe.com/static/add-on-sdk/sdk.js";

const sandboxApi = await addOnUISdk.instance.runtime.apiProxy("documentSandbox");
await sandboxApi.addTextToDocument("Hello World");

Workflow 6: Implement Iframe ↔ Sandbox Communication

When you need: To pass data between UI and document manipulation code.

Pattern:

In Document Sandbox (code.js):

import addOnSandboxSdk from "add-on-sdk-document-sandbox";

const api = {
  async addTextToDocument(text) {
    // Document manipulation logic
  }
};

addOnSandboxSdk.instance.runtime.exposeApi(api);

In Iframe Runtime (index.js):

import addOnUISdk from "https://express.adobe.com/static/add-on-sdk/sdk.js";

const sandboxApi = await addOnUISdk.instance.runtime.apiProxy("documentSandbox");
await sandboxApi.addTextToDocument("Hello World");

Workflow 7: Use Code Samples as Starting Points

When you need: Implementation examples, starter code, or best practices.

Steps:

1. Read

   references/code-samples.md

   to find relevant sample
2. Clone sample repo:

   git clone https://github.com/AdobeDocs/express-add-on-samples.git

3. Navigate to sample:

   cd express-add-on-samples/samples/<sample-name>

4. Install and run:

   npm install && npm run build && npm run start

5. Study the code and adapt to your needs

Recommended samples:

• OAuth/Cloud Storage:

  import-images-using-oauth

  (copy OAuthUtils.js!)
• Data Persistence:

  use-client-storage

• Export Renditions:

  export-sample

• Audio Handling:

  audio-recording-addon

• React + Spectrum:

  swc-react-theme-sampler

• Vanilla JS:

  swc

Workflow 8: Debug Common Issues

Issue:

undefined

• Solution: Check import pattern (default vs named)
• Verify you're using the correct SDK for the runtime environment

Issue: "Cannot access DOM" in document sandbox

• Solution: Move DOM code to iframe runtime; pass data via communication APIs

Issue: API not working as expected

• Solution: Query MCP server for latest documentation
• Check if API is marked as experimental (requires manifest permissions)

Issue: Manifest errors

• Solution: Verify

  "documentSandbox"

  path matches your build setup
• No-build:

  "sandbox/code.js"

  (full path)
• Build:

  "code.js"

  (webpack output)

Best Practices

1. Always query MCP server for latest API documentation before implementing features
2. Separate concerns: UI in iframe runtime, document manipulation in sandbox
3. Use TypeScript definitions for better IDE support and error catching
4. Follow Spectrum design for consistent user experience
5. Test in Adobe Express development mode early and often
6. Handle errors gracefully with user-friendly messages
7. Respect permissions - request only what you need in manifest.json
8. Cache intelligently - use ClientStorage for user preferences

MCP Server Tools Available

get_relevant_documentations

get_typedefinitions

api_type: "express-document-sdk"

Common File Paths

• Manifest:

  src/manifest.json

• Iframe UI:

  src/index.html

  ,

  src/ui/index.js

• Document Sandbox:

  src/sandbox/code.js

• Styles:

  src/ui/styles.css

  (never in sandbox)
• Config:

  webpack.config.js

  ,

  tsconfig.json

Troubleshooting

.vscode/mcp.json

Bundled References

This skill includes detailed reference documentation in the

references/

OAuth Implementation Guide

File:

references/oauth-implementation.md

Complete OAuth 2.0 implementation guide with:

• PKCE flow step-by-step
• OAuthUtils.js helper module documentation
• Provider configurations (Dropbox, OneDrive, Google Drive, Box)
• Token storage patterns
• Login/logout UI examples
• Error handling patterns

Use when: Implementing OAuth authentication, cloud storage integration, or user authentication.

Code Samples Index

File:

references/code-samples.md

Comprehensive catalog of 13 official Adobe Express add-on samples:

• import-images-using-oauth ⭐ - Complete OAuth + cloud storage example (COPY OAuthUtils.js from here!)
• use-client-storage - Data persistence patterns
• export-sample - Export renditions in multiple formats
• audio-recording-addon - Media handling
• pix - Advanced canvas-based editor
• Plus 8 more samples covering React, Vue, Spectrum, and more

Use when: Looking for implementation examples, starter code, or best practices.

External References

• Adobe Express Add-ons Docs: developer.adobe.com/express/add-ons
• Spectrum Web Components: opensource.adobe.com/spectrum-web-components
• Code Samples Repository: github.com/AdobeDocs/express-add-on-samples
• OAuthUtils.js Source: OAuthUtils.js
• Code Playground: Test add-on code directly in Adobe Express
• CLI Tool:

  npx @adobe/create-express-add-on

  for scaffolding projects

Quick Tips

• Global await: Only works in Code Playground Script Mode, not in actual add-ons
• CSS location: ALWAYS in iframe runtime, NEVER in document sandbox
• Singleton SDKs: Import once, use throughout - never instantiate
• OAuth domains: Add to

  manifest.json

  permissions before using
• Audio API:

  title

  parameter is MANDATORY
• Video API:

  title

  parameter is OPTIONAL
• Build vs No-build: Build templates support JSX, TypeScript, modern JavaScript