Electron Desktop Applications

Quick Guide: Electron apps run two process types: a main process (Node.js, manages windows and system APIs) and renderer processes (Chromium, one per window). All communication between them flows through IPC via a preload script that uses contextBridge to expose a minimal, typed API surface. Never disable contextIsolation. Never enable nodeIntegration in renderers. Package with Electron Forge or Electron Builder. Auto-update via autoUpdater (Squirrel on macOS/Windows) or electron-updater for all platforms.

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<critical_requirements>

CRITICAL: Before Using This Skill

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST keep contextIsolation: true (the default) -- disabling it exposes the entire preload scope to untrusted renderer code)

(You MUST use contextBridge.exposeInMainWorld() in preload scripts -- never expose ipcRenderer directly)

(You MUST NOT enable nodeIntegration: true in any BrowserWindow -- it gives renderers full Node.js access, which is a critical security vulnerability)

(You MUST validate and sanitize ALL data received via IPC in the main process -- treat renderer messages as untrusted input)

(You MUST use ipcMain.handle() / ipcRenderer.invoke() for request-response IPC -- avoid sendSync which blocks the renderer)

(You MUST NOT load remote URLs with nodeIntegration or disabled contextIsolation -- this is equivalent to giving the remote site full system access)

</critical_requirements>

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Auto-detection: Electron, electron, BrowserWindow, ipcMain, ipcRenderer, contextBridge, preload, webPreferences, electron-builder, electron-forge, app.whenReady, electronAPI, mainWindow, autoUpdater, nativeTheme, safeStorage, Tray, Menu, dialog, protocol, shell

When to use:

• Building cross-platform desktop applications
• Configuring main process / renderer process architecture
• Setting up secure IPC communication patterns
• Integrating with native OS features (tray, menus, dialogs, notifications, file system)
• Packaging and distributing desktop applications
• Implementing auto-update functionality
• Registering custom protocol handlers / deep links

When NOT to use:

• Choosing a UI framework for the renderer (use the appropriate web framework skill)
• Styling the renderer UI (use the appropriate styling skill)
• Server-side or backend logic not related to the main process
• Mobile applications (Electron is desktop-only)
• CLI tools that do not need a GUI

---

Key Patterns

Pattern 1: Secure BrowserWindow Creation

Every BrowserWindow must use a preload script and rely on the secure defaults: contextIsolation: true, sandbox: true, nodeIntegration: false.

const mainWindow = new BrowserWindow({
  width: 1200,
  height: 800,
  webPreferences: {
    preload: path.join(__dirname, "preload.js"),
    // contextIsolation: true  -- default since Electron 12
    // sandbox: true           -- default since Electron 20
    // nodeIntegration: false  -- default since Electron 5
  },
});

Key point: Never override the security defaults. The preload script is the ONLY bridge between main and renderer. See examples/core.md.

---

Pattern 2: Preload with contextBridge

The preload script exposes a narrow, explicitly typed API to the renderer. Never expose ipcRenderer directly.

// preload.js
const { contextBridge, ipcRenderer } = require("electron");

contextBridge.exposeInMainWorld("electronAPI", {
  readFile: (filePath) => ipcRenderer.invoke("read-file", filePath),
  onUpdateAvailable: (callback) => {
    ipcRenderer.on("update-available", (_event, data) => callback(data));
  },
});

Key point: Each exposed method wraps a single IPC channel. The renderer calls window.electronAPI.readFile(path) with no knowledge of IPC internals. See examples/core.md.

---

Pattern 3: IPC Request-Response (invoke/handle)

Use ipcMain.handle() in main and ipcRenderer.invoke() in preload for async two-way communication.

// main process
ipcMain.handle("read-file", async (_event, filePath) => {
  const content = await fs.readFile(filePath, "utf-8");
  return { success: true, content };
});

Key point: handle/invoke returns a Promise. Always validate filePath in the handler -- never trust renderer input. See examples/ipc.md for all IPC patterns.

---

Pattern 4: Main-to-Renderer Messages

Use webContents.send() from main and listen in the preload with a callback pattern.

// main: send to specific window
mainWindow.webContents.send("update-progress", { percent: 45 });

// preload: expose listener
onUpdateProgress: (callback) => {
  ipcRenderer.on("update-progress", (_event, data) => callback(data));
},

Key point: The renderer cannot pull from main -- main must push. Always scope listeners to specific channels. See examples/ipc.md.

---

Pattern 5: App Lifecycle

The main process manages the app lifecycle with platform-specific conventions.

app.whenReady().then(() => {
  createWindow();
  app.on("activate", () => {
    if (BrowserWindow.getAllWindows().length === 0) createWindow();
  });
});

app.on("window-all-closed", () => {
  if (process.platform !== "darwin") app.quit();
});

Key point: macOS apps stay alive when all windows close (window-all-closed should not quit). The activate event recreates a window when the dock icon is clicked. See examples/core.md.

---

Pattern 6: Native OS Integration

Electron exposes native APIs for dialogs, menus, tray icons, notifications, and more -- all accessed from the main process.

const { dialog } = require("electron");

const result = await dialog.showOpenDialog(mainWindow, {
  properties: ["openFile", "multiSelections"],
  filters: [{ name: "Documents", extensions: ["txt", "md", "json"] }],
});

Key point: Native dialogs are modal to a window when passed mainWindow as the first argument. See examples/native-apis.md.

---

Pattern 7: Custom Protocol / Deep Linking

Register your app to handle myapp:// URLs for deep linking from browsers or other apps.

if (process.defaultApp) {
  app.setAsDefaultProtocolClient("myapp", process.execPath, [
    path.resolve(process.argv[1]),
  ]);
} else {
  app.setAsDefaultProtocolClient("myapp");
}

Key point: In development (process.defaultApp is true), you must pass the script path as an argument. On macOS, handle the open-url event on the app object. On Windows/Linux, handle via second-instance event. See examples/native-apis.md.

---

<decision_framework>

Decision Framework

IPC Pattern Selection

Which IPC pattern?
+-- Renderer needs a response from main?
|   +-- YES --> ipcMain.handle() + ipcRenderer.invoke()
+-- Renderer sends data, no response needed?
|   +-- YES --> ipcMain.on() + ipcRenderer.send()
+-- Main needs to push data to renderer?
|   +-- YES --> webContents.send() + ipcRenderer.on() (in preload)
+-- Two renderers need to communicate?
|   +-- YES --> Route through main process (never direct renderer-to-renderer)
+-- High-frequency data transfer (streaming)?
    +-- YES --> MessageChannelMain / MessagePort pair

Window Architecture

How many windows?
+-- Single window app?
|   +-- One BrowserWindow, one preload script
+-- Multi-window (e.g., preferences, about)?
|   +-- Separate BrowserWindow per view, each with its own preload
+-- Frameless / custom title bar?
|   +-- frame: false + custom drag regions via CSS (-webkit-app-region: drag)
+-- Persistent background work?
    +-- Use a hidden BrowserWindow or utilityProcess (Electron 22+)

</decision_framework>

---

Detailed resources:

• examples/core.md - App lifecycle, BrowserWindow, preload, contextBridge fundamentals
• examples/ipc.md - All IPC patterns: invoke/handle, send/on, main-to-renderer, MessagePort
• examples/security.md - Security hardening, CSP, permission handlers, safe defaults
• examples/native-apis.md - Dialogs, menus, tray, notifications, protocol handlers, auto-updater
• examples/packaging.md - Electron Forge, Electron Builder, code signing, distribution
• reference.md - API quick-reference tables, version history, security checklist

---

<red_flags>

RED FLAGS

Critical Security Issues:

• Disabling contextIsolation (contextIsolation: false) -- exposes preload globals to renderer
• Enabling nodeIntegration: true -- gives renderer full Node.js access (fs, child_process, etc.)
• Exposing ipcRenderer directly via contextBridge instead of wrapping individual channels
• Loading remote/untrusted URLs without sandbox: true
• Disabling webSecurity in production (webSecurity: false disables same-origin policy)
• Not validating IPC arguments in main process handlers (path traversal, injection attacks)
• Using shell.openExternal() with unvalidated URLs (can execute arbitrary commands)

Architecture Issues:

• Using ipcRenderer.sendSync() -- blocks the renderer process, causes UI freezes
• Putting business logic in the renderer instead of the main process
• Direct renderer-to-renderer communication (bypassing main)
• Using remote module (removed in Electron 14+, was a security and performance hazard)
• Creating BrowserWindows from the renderer process
• Not handling window-all-closed per-platform (macOS apps should not quit)

Packaging Issues:

• Shipping devDependencies in production builds (bloated app size)
• Not code-signing the application (OS warnings, auto-update failures on macOS)
• Bundling node_modules without pruning or using ASAR archive
• Hardcoding absolute paths that differ between dev and packaged environments
• Using __dirname in renderer code (unavailable in sandboxed renderers)

Common Mistakes:

• Forgetting app.whenReady() -- APIs are unavailable before the ready event
• Not re-creating window on activate event (macOS dock click does nothing)
• Using require() in renderer scripts loaded via <script> tags (not available in sandboxed renderers)
• Setting nodeIntegrationInSubFrames: true for iframes loading external content
• Not setting proper Content-Security-Policy headers for renderer HTML

</red_flags>

---

<critical_reminders>

CRITICAL REMINDERS

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST keep contextIsolation: true (the default) -- disabling it exposes the entire preload scope to untrusted renderer code)

(You MUST use contextBridge.exposeInMainWorld() in preload scripts -- never expose ipcRenderer directly)

(You MUST NOT enable nodeIntegration: true in any BrowserWindow -- it gives renderers full Node.js access, which is a critical security vulnerability)

(You MUST validate and sanitize ALL data received via IPC in the main process -- treat renderer messages as untrusted input)

(You MUST use ipcMain.handle() / ipcRenderer.invoke() for request-response IPC -- avoid sendSync which blocks the renderer)

Failure to follow these rules will create severe security vulnerabilities or broken desktop applications.

</critical_reminders>