# Cometchat Core

> Shared rules for CometChat React UI Kit v6. Always loaded alongside framework + placement skills. Read this first.

- Skill: `cometchat/cometchat-core` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cometchat/cometchat-core`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cometchat/cometchat-core/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Design & Media
- License: MIT
- Author: cometchat (https://skillmd.com/u/cometchat)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/cometchat/cometchat-core

---


> **Ground truth:** the installed `@cometchat/chat-uikit-react@^6` + `@cometchat/chat-sdk-javascript@^4` package types (`node_modules/@cometchat/chat-uikit-react`) + `docs/ui-kit/react`. **Official docs:** https://www.cometchat.com/docs/ui-kit/react/overview · **Docs MCP:** `claude mcp add --transport http cometchat-docs https://www.cometchat.com/docs/mcp` (or fetch the URL directly on agents without MCP). Verify any non-obvious symbol against the installed package types before relying on it.

## Purpose

This is the foundational skill for every CometChat React UI Kit v6 integration. It teaches Claude HOW CometChat works -- initialization, login, CSS, environment variables, SSR safety, and the provider pattern -- so Claude can write project-appropriate code instead of relying on templates.

**Read this skill first, before any framework or placement skill.**

## When to use

- Any React-family integration: Vite + React, Next.js (App or Pages Router), React Router v6/v7, Astro with React islands.
- BEFORE loading any framework-specific patterns skill (`cometchat-react-patterns`, `cometchat-nextjs-patterns`, etc.) — those layer on top of this.
- When the user is asking about CometChat init, login, env vars, CSS, provider pattern, SSR safety, or production auth.

## When NOT to use

- **React Native** (Expo or bare) — load `cometchat-native-core` instead. The wrappers, env-var prefixes, and lifecycle are different.
- **Angular** — load `cometchat-angular-core`. Uses `APP_INITIALIZER` + `CUSTOM_ELEMENTS_SCHEMA` + `environment.ts`, not React's provider chain.
- **Native Android (V5 or V6)** — load `cometchat-android-v5-core` or `cometchat-android-v6-core`. Kotlin init, `local.properties` credentials.
- **Native iOS (V5)** — load `cometchat-ios-core`. Swift init, CocoaPods/SPM.
- **Flutter (V5 or V6)** — load `cometchat-flutter-v5-core` or `cometchat-flutter-v6-core`. Dart init via `pubspec.yaml`.
- **Backend-only token-mint server work** — load `cometchat-production` for the REST-API token recipes; this skill is client-side.

## Common Rationalizations — and why they're wrong

A two-column anti-skip defense. Every excuse below has been used by agents (or could plausibly be) to skip rules in this skill. The rebuttal cites the validated incident.

| Excuse the agent might invent | Reality |
|---|---|
| "StrictMode double-invocation is a dev-only quirk, so I can skip the in-flight login promise pattern (§2)" | The same race fires anywhere a parent component re-mounts (React Router v6 nested routes, Suspense boundary retries, error-boundary resets). Skipping yields the canonical `"Please wait until the previous login request ends"` error on production refreshes too. |
| "This is a quick prototype, I'll hardcode `cometchat-uid-1` instead of asking the user" | Two testers shipped apps where the default UID was a Bot in their dashboard (ENG-35717). Auth-key login refuses bot users by design; the error `Auth token creation not allowed for this bot <uid>` is opaque. **Always ask via the dispatcher's Step 3d.1 prompt.** |
| "I'll use `setError(String(e))` for now and pretty-print later" | `String(e)` on a CometChatException renders `[object Object]` — testers wasted 10-minute debugging sessions on this (ENG-35719). Always emit the §6 `formatCometChatError` helper from `cometchat/errors.ts`. "Later" never comes. |
| "The env file looks right, I don't need to run `config show --json`" | Two testers shipped code with empty `VITE_COMETCHAT_APP_ID` because the dispatcher moved on without confirming (ENG-35718). The pre-flight is 1 second; the cost of skipping is a customer-facing init failure. |
| "I know React, I can skip reading the framework-specific patterns skill" | The framework patterns carry version-pinned traps that aren't in training data: the Next.js 15+ rule `dynamic(ssr:false)` must live in a Client Component (verified by runtime smoke 2026-06-02), the Vite Visual Builder `tsconfig` patches (resolveJsonModule, jsx: react-jsx, verbatimModuleSyntax: false), the React Router v7 `appDirectory` constraint. Skipping = customer-visible build failure. |
| "I'll add the telemetry hook later; the basic provider works without it" | The telemetry prop is opt-in by design (no-op if not passed) — but the four lifecycle events (init_started / init_finished / login_started / login_finished + their _failed variants) are how customers wire analytics into onboarding funnels without monkey-patching. Skipping ENG-35715 wiring means the customer has to refactor their provider post-launch. |

## Red flags — signs you're misapplying this skill

- The agent emitted `setError(String(e))` anywhere in code — should be `setError(formatCometChatError(e))` per §6 (ENG-35719).
- The agent's plan (Step 3f) doesn't include `cometchat/errors.ts` as a created file.
- The agent emitted bare `CometChatUIKit.login(uid)` without the in-flight-promise guard (`ensureLoggedIn`) — guaranteed StrictMode race in dev.
- A `<style>` or CSS rule targets internal class names like `.cometchat-conversation-list-item` (anti-pattern §8.3) instead of the `--cometchat-*` CSS variables.
- The agent picked `cometchat-uid-1` without asking the user (ENG-35717 — the bot-flag failure mode).
- The agent's env file uses the wrong framework prefix (e.g., `VITE_*` in a Next.js project, or `EXPO_PUBLIC_*` in a Vite project).
- The provider doesn't gate `{children}` on `isReady` — chat components mount before init completes and throw `CometChat is not initialized` errors.

## Verification — before declaring this skill applied

Run through this checklist before saying "done" for any task that touched cometchat-core territory:

- [ ] `grep -nE "setError\(String\(" src/` returns ZERO matches (ENG-35719 — must use `formatCometChatError`).
- [ ] `src/cometchat/errors.ts` exists and exports `formatCometChatError` + `logCometChatError`.
- [ ] The provider has an `ensureLoggedIn`-style in-flight guard (no bare `CometChatUIKit.login` calls).
- [ ] `tsc --noEmit` passes against the project's existing `tsconfig`.
- [ ] Env vars use the **detected framework's prefix** (`VITE_*` / `NEXT_PUBLIC_*` / `PUBLIC_*` / `EXPO_PUBLIC_*`), and `.env` (or `.env.local` for Next.js) is in `.gitignore`.
- [ ] CSS imports happen once at the entry / root (per framework section in §3).
- [ ] If the user is on Next.js: the page that owns CometChat components has `"use client"` (App Router) or is dynamic-imported with `ssr: false` (App Router only inside another Client Component, per the Next.js 15+ rule verified 2026-06-02).
- [ ] The user confirmed the dev-mode UID via the dispatcher's Step 3d.1 prompt — NOT silently picked.

---

## 1. Initialization

CometChat must be initialized exactly once before any UI component renders. Initialization is asynchronous and must complete fully before mounting any `CometChat*` component.

### File-based init with `cometchat-settings.json` (recommended)

> **Version requirement (ENG-35866 — Skills Telemetry).** `CometChatUIKit.initFromSettings(settings)` reads a `cometchat-settings.json` object and lets the SDK self-report `integrationSource = "ai-agent"` to `/user_sessions`. It ships GA in **`@cometchat/chat-uikit-react >= 6.5.2`** + **`@cometchat/chat-sdk-javascript >= 4.1.11`** (npm `latest`). On an older UI Kit the method does not exist — use the **`UIKitSettingsBuilder` fallback** below.

**Step 1 — create `cometchat-settings.json` at the project root.** Fill `appId` / `region` / `credentials.authKey` from the CLI `provision setup` output; leave everything else at the defaults below. This is the single source of credentials — no second copy to keep in sync.

```json
{
  "appId": "APP_ID_HERE",
  "region": "us",
  "credentials": {
    "authKey": "AUTH_KEY_HERE"
  },
  "chatSDK": {
    "presenceSubscription": {
      "type": "ALL_USERS",
      "roles": []
    },
    "autoEstablishSocketConnection": true,
    "adminHost": null,
    "clientHost": null
  },
  "callsSDK": {
    "host": null,
    "adminHost": null,
    "clientHost": null,
    "callsHost": null
  },
  "uiKit": {
    "subscribePresenceForAllUsers": true
  }
}
```

**Step 2 — init by importing the JSON as a build-time module.** Vite, CRA, Next.js, and Astro all have `resolveJsonModule` on by default, so the import is type-safe with no extra config:

```typescript
// initFromSettings ships GA in @cometchat/chat-uikit-react >= 6.5.2 (ENG-35866)
import { CometChatUIKit } from "@cometchat/chat-uikit-react";
import cometchatSettings from "./cometchat-settings.json"; // adjust path to the file's location

await CometChatUIKit.initFromSettings(cometchatSettings);
```

- **Commit `cometchat-settings.json` — do not gitignore it** (the file is part of the integration). Its `authKey` is an **optional demo/POC credential**: a quick-start affordance so a PM or developer can see working chat *before* the backend auth-token flow is wired (that flow often waits on internal approvals). Because the file is committed to source control, treat the key as public — use a **dedicated demo CometChat app** (a committed key trips secret scanners and stays in git history; never reuse a production app's key). Switch to a server-minted `authToken` via `loginWithAuthToken` before production, where `authKey` must not ship.
- The same module-flag / `useEffect` / entry-point placement rules in the rest of this section apply unchanged — just swap `CometChatUIKit.init(settings)` for `CometChatUIKit.initFromSettings(cometchatSettings)`.

### The UIKitSettingsBuilder (fallback — UI Kit before file-based init)

```typescript
import { CometChatUIKit, UIKitSettingsBuilder } from "@cometchat/chat-uikit-react";

const settings = new UIKitSettingsBuilder()
  .setAppId(APP_ID)       // Required. String from the CometChat dashboard.
  .setRegion(REGION)       // Required. "us", "eu", "in", etc.
  .setAuthKey(AUTH_KEY)    // Required for dev mode. Omit in production (use auth tokens).
  .subscribePresenceForAllUsers() // Optional but recommended -- enables online/offline indicators.
  .build();
```

### Init must happen once

Use a module-level flag to prevent double-init. This is critical because React StrictMode in development calls effects twice:

```typescript
let initialized = false;

async function initCometChat(): Promise<void> {
  if (initialized) return;
  initialized = true;

  // Fail loud if env vars didn't load. Empty credentials otherwise surface
  // much later as a cryptic `ERROR_API_KEY_NOT_FOUND` / failed init that's hard
  // to trace back to a missing/mis-prefixed .env. (audit P0-5)
  if (!APP_ID || !REGION || !AUTH_KEY) {
    throw new Error(
      "CometChat credentials are empty — check .env and the framework's env prefix " +
        "(VITE_ / NEXT_PUBLIC_ / PUBLIC_), and restart the dev server after editing .env.",
    );
  }

  const settings = new UIKitSettingsBuilder()
    .setAppId(APP_ID)
    .setRegion(REGION)
    .setAuthKey(AUTH_KEY)
    .subscribePresenceForAllUsers()
    .build();

  await CometChatUIKit.init(settings);
}
```

### Init must be in useEffect (React components) or before mount (entry files)

**In a useEffect (Next.js, Astro, React Router SSR):**

```typescript
useEffect(() => {
  initCometChat()
    .then(() => loginUser())
    .then(() => setReady(true))
    .catch((e) => setError(String(e)));
}, []);
```

**At the entry point (Vite/CRA -- no SSR):**

```typescript
// main.tsx -- runs once, before React mounts
CometChatUIKit.init(settings)
  ?.then(() => CometChatUIKit.login("cometchat-uid-1"))
  .then(() => mount())
  .catch((e) => mountError(String(e)));
```

The init-at-entry pattern works for Vite/CRA because `main.tsx` only runs in the browser. For frameworks with SSR (Next.js, Astro, React Router v7 SSR), you MUST use the useEffect pattern because the module runs on the server first.

---

## 2. Login

### Development mode

Use `CometChatUIKit.login(uid)` with a test UID. Every new CometChat app comes with five pre-created test users: `cometchat-uid-1` through `cometchat-uid-5`.

```typescript
const user = await CometChatUIKit.getLoggedinUser();
if (!user) {
  await CometChatUIKit.login("cometchat-uid-1");
}
```

### ⚠️ `login()` is safe to call sequentially, NOT concurrently

A subtle but important distinction:

- **Sequential** (first `login()` completes, then second is called): the SDK's second call returns immediately with the already-logged-in user. Safe.
- **Concurrent** (a second `login()` fires while the first is still in-flight): the SDK throws `"Please wait until the previous login request ends."` The user sees a red error on the page, has to refresh, and only then does it work (because the first session is now cached).

This is exactly the case that React 18 StrictMode triggers in development: effects run mount → unmount → mount, so a `useEffect` that calls `login()` fires twice with no time for the first call to finish. Production builds don't double-mount, but any code path that can call `login()` from two places simultaneously hits the same error.

**Guard concurrent login with a module-level in-flight promise:**

```typescript
let loginInFlight: Promise<unknown> | null = null;

async function ensureLoggedIn(
  uid: string,
  authToken?: string,
): Promise<void> {
  const existing = await CometChatUIKit.getLoggedinUser();
  // Same user already logged in → nothing to do (sequential case).
  if (existing && existing.getUid?.() === uid) return;
  // A DIFFERENT user is logged in (account switch, or logout → login-as-other).
  // Log out first: otherwise the SDK keeps the old session and login() silently
  // no-ops, so the app shows the previous account. (Switching accounts requires
  // an explicit logout — login() is a no-op against an existing session.)
  if (existing) await CometChatUIKit.logout();
  if (loginInFlight) {                   // concurrent case — reuse pending promise
    await loginInFlight;
    return;
  }
  loginInFlight = authToken
    ? CometChatUIKit.loginWithAuthToken(authToken)
    : CometChatUIKit.login(uid);
  try {
    await loginInFlight;
  } finally {
    loginInFlight = null;
  }
}
```

Call `ensureLoggedIn()` from the provider / effect instead of `CometChatUIKit.login()` directly. Both StrictMode mounts resolve against the same promise, so only one login request actually hits the server.

**Why not just a boolean flag?** A boolean would require extra wait-loop code to handle "login started but not finished yet." A cached promise handles that automatically — `await` on the same promise is free for all callers.

### Getting the current logged-in UID in app code

When your integration code needs the current user's UID (for example, to decide which conversation to target, or to filter by sender), **always fetch it from the SDK — never hardcode a UID like `"cometchat-uid-1"`**.

Two getters, for different contexts. **Default to the sync version** — it matches the v6 sample app and works for almost all app code, because by the time UI components render, the kit's init + login flow is already complete:

```typescript
// ✓ Preferred — sync, returns User | null directly. Use this in app code.
import { CometChatUIKitLoginListener } from "@cometchat/chat-uikit-react";
const me = CometChatUIKitLoginListener.getLoggedInUser();  // note capital `I` in `InUser`
const myUid = me?.getUid();

// Fallback — async, for the bootstrap path where init may not be complete
// (e.g., inside the provider's init effect, or before the first login resolves).
const me = await CometChatUIKit.getLoggedinUser();
const myUid = me?.getUid();
```

The sync `CometChatUIKitLoginListener.getLoggedInUser()` is the right call from any component that mounts AFTER login completes — which is virtually all of them, since the dispatcher's recipes put login on a dedicated route or in the provider's init effect that gates rendering. Reach for the async `CometChatUIKit.getLoggedinUser()` only when you're inside that init effect itself.

**Casing matters.** Note `getLogged**In**User` (capital `I`) on the LoginListener vs `getLogged**in**User` (lowercase `i`) on `CometChatUIKit` — both casings exist in the kit, they're different methods.

Hardcoding `"cometchat-uid-1"` only works in the dev mode login call (`CometChatUIKit.login("cometchat-uid-1")`) because you're *choosing* who to log in as. Once logged in, the getters are the source of truth — useful when the logged-in user comes from production auth (a real user ID, not a test UID), or when the user logs out and logs in as someone else.

### Production mode

Use `CometChatUIKit.loginWithAuthToken(token)` with a token obtained from your backend. The backend generates the token using the CometChat REST API with your `AUTH_TOKEN` (not the client-side `AUTH_KEY`).

```typescript
// Fetch token from YOUR backend, which calls CometChat's REST API
const response = await fetch("/api/cometchat-token", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({ uid: currentUser.id }),
});
const { token } = await response.json();

await CometChatUIKit.loginWithAuthToken(token);
```

For the full production auth setup, use `npx @cometchat/skills-cli production-auth`. Never hardcode auth keys in source code that ships to production.

### Logout

```typescript
await CometChatUIKit.logout();
```

Call this when the user signs out of your application. This clears CometChat's local session.

---

## 3. CSS

### Import once at the app root

```typescript
import "@cometchat/chat-uikit-react/css-variables.css";
```

This import MUST appear exactly once, at the highest level of your application:

| Framework | Where to import |
|---|---|
| React (Vite) | `src/main.tsx` or `src/index.css` via `@import` |
| Next.js (App Router) | `app/globals.css` via `@import` or `app/layout.tsx` |
| Next.js (Pages Router) | `pages/_app.tsx` or `styles/globals.css` |
| Astro | Global layout file or `src/styles/global.css` |
| React Router | Root route module or `app/root.tsx` |

### Theming with CSS variables

All CometChat components respect `--cometchat-*` CSS variables. Override them on a parent element or `:root`:

```css
:root {
  --cometchat-primary-color: #6851d6;
  --cometchat-background-color-01: #ffffff;
  --cometchat-text-color-primary: #141414;
  --cometchat-font-family: "Inter", sans-serif;
  --cometchat-border-radius-lg: 12px;
}
```

### Never target internal class names

CometChat's internal class names (like `.cometchat-message-bubble__wrapper`) are not part of the public API and may change between versions. Always use CSS variables for customization. The only exception is when explicitly copying patterns from the v6 sample app that use documented BEM class names.

---

## 4. Environment variables

Each framework has its own convention for exposing env vars to client-side code. CometChat needs three variables: `APP_ID`, `REGION`, and `AUTH_KEY`.

### Per-framework naming

| Framework | Prefix | Example |
|---|---|---|
| React (Vite) | `VITE_` | `import.meta.env.VITE_COMETCHAT_APP_ID` |
| Next.js | `NEXT_PUBLIC_` | `process.env.NEXT_PUBLIC_COMETCHAT_APP_ID` |
| Astro | `PUBLIC_` | `import.meta.env.PUBLIC_COMETCHAT_APP_ID` |
| React Router (Vite) | `VITE_` | `import.meta.env.VITE_COMETCHAT_APP_ID` |
| CRA | `REACT_APP_` | `process.env.REACT_APP_COMETCHAT_APP_ID` |

### The three variables

| Variable suffix | Required | Description |
|---|---|---|
| `COMETCHAT_APP_ID` | Yes | Your app ID from the CometChat dashboard |
| `COMETCHAT_REGION` | Yes | Region code: `"us"`, `"eu"`, `"in"`, etc. |
| `COMETCHAT_AUTH_KEY` | Dev only | Client-side auth key. Replace with auth tokens for production. |

### .env file placement

| Framework | File | Gitignored by default |
|---|---|---|
| Vite / React Router | `.env` | No -- add to `.gitignore` |
| Next.js | `.env.local` | Yes |
| Astro | `.env` | No -- add to `.gitignore` |
| CRA | `.env` | No -- add to `.gitignore` |

---

## 5. SSR safety

All CometChat UI Kit components are browser-only. They access `window`, `document`, and browser APIs during import. Rendering them on the server will crash.

### Framework-specific SSR prevention

**Next.js (App Router):**

Mark the file containing CometChat components with `"use client"` at the top. Use `next/dynamic` with `ssr: false` if the component is imported from a server component:

```typescript
"use client";
// This entire file only runs in the browser

import { CometChatConversations } from "@cometchat/chat-uikit-react";
```

Or from a server component:

```typescript
import dynamic from "next/dynamic";

const ChatView = dynamic(() => import("./ChatView"), { ssr: false });
```

**Next.js (Pages Router):**

Use `next/dynamic` with `ssr: false`:

```typescript
import dynamic from "next/dynamic";

const CometChatNoSSR = dynamic(() => import("../components/CometChatNoSSR"), {
  ssr: false,
});
```

**Astro:**

Use the `client:only="react"` directive. This prevents the component from rendering during Astro's static build:

```astro
---
import ChatPanel from "../components/ChatPanel";
---
<ChatPanel client:only="react" />
```

**React Router v7 (SSR mode):**

Use `React.lazy()` with `Suspense` in a `clientLoader` or `useEffect` guard:

```typescript
import { lazy, Suspense } from "react";

const ChatView = lazy(() => import("./ChatView"));

export default function ChatRoute() {
  const [mounted, setMounted] = useState(false);
  useEffect(() => setMounted(true), []);

  if (!mounted) return null;
  return (
    <Suspense fallback={<div>Loading chat...</div>}>
      <ChatView />
    </Suspense>
  );
}
```

**React (Vite / CRA):**

No SSR concerns. These are client-only by nature. Import and use directly.

---

## 6. Provider pattern

Instead of inlining init/login logic in every component, create a reusable `CometChatProvider` that handles initialization, login, and ready-state gating. Wrap your chat UI with it.

```typescript
// CometChatProvider.tsx
"use client"; // Required for Next.js App Router; harmless in other frameworks

import React, { useEffect, useState, createContext, useContext } from "react";
import { CometChatUIKit, UIKitSettingsBuilder } from "@cometchat/chat-uikit-react";

interface CometChatContextValue {
  isReady: boolean;
  error: string | null;
}

const CometChatContext = createContext<CometChatContextValue>({
  isReady: false,
  error: null,
});

export const useCometChat = () => useContext(CometChatContext);

// Module-level state: shared across all mounts so React 18 StrictMode's
// double-invocation of effects doesn't fire init or login twice.
let initialized = false;
let loginInFlight: Promise<unknown> | null = null;

async function ensureLoggedIn(
  uid: string,
  authToken?: string,
): Promise<void> {
  const existing = await CometChatUIKit.getLoggedinUser();
  if (existing) return;
  if (loginInFlight) {
    // A prior StrictMode mount (or another effect) already started login —
    // reuse its promise instead of calling login() a second time, which
    // throws "Please wait until the previous login request ends."
    await loginInFlight;
    return;
  }
  loginInFlight = authToken
    ? CometChatUIKit.loginWithAuthToken(authToken)
    : CometChatUIKit.login(uid);
  try {
    await loginInFlight;
  } finally {
    loginInFlight = null;
  }
}

// ENG-35715 telemetry hook — opt-in callback for init/login lifecycle.
// Fires at six phases. If `telemetry` prop is not passed, all calls are no-ops.
export type CometChatTelemetryEvent =
  | { phase: "init_started";    appId: string; region: string }
  | { phase: "init_finished";   durationMs: number }
  | { phase: "init_failed";     error: unknown }
  | { phase: "login_started";   uid: string; mode: "authKey" | "authToken" }
  | { phase: "login_finished";  durationMs: number }
  | { phase: "login_failed";    error: unknown };

interface CometChatProviderProps {
  appId: string;
  region: string;
  authKey?: string;
  authToken?: string;
  uid?: string;
  telemetry?: (event: CometChatTelemetryEvent) => void;   // ← opt-in lifecycle hook
  children: React.ReactNode;
}

export function CometChatProvider({
  appId,
  region,
  authKey,
  authToken,
  uid = "cometchat-uid-1",
  telemetry,
  children,
}: CometChatProviderProps) {
  const [isReady, setIsReady] = useState(false);
  const [error, setError] = useState<string | null>(null);

  useEffect(() => {
    async function setup() {
      const initStart = performance.now();
      try {
        if (!initialized) {
          initialized = true;
          telemetry?.({ phase: "init_started", appId, region });
          const builder = new UIKitSettingsBuilder()
            .setAppId(appId)
            .setRegion(region)
            .subscribePresenceForAllUsers();

          if (authKey) {
            builder.setAuthKey(authKey);
          }

          const settings = builder.build();
          await CometChatUIKit.init(settings);
          telemetry?.({ phase: "init_finished", durationMs: performance.now() - initStart });
        }

        const loginStart = performance.now();
        telemetry?.({ phase: "login_started", uid, mode: authToken ? "authToken" : "authKey" });
        await ensureLoggedIn(uid, authToken);
        telemetry?.({ phase: "login_finished", durationMs: performance.now() - loginStart });

        setIsReady(true);
      } catch (e) {
        // If init never completed, this is an init_failed; otherwise login_failed.
        const phase = isReady ? "login_failed" : "init_failed";
        telemetry?.({ phase, error: e } as CometChatTelemetryEvent);
        setError(formatCometChatError(e));
      }
    }

    setup();
  }, [appId, region, authKey, authToken, uid, telemetry]);

  if (error) {
    return (
      <div style={{ color: "red", padding: 16, fontFamily: "monospace" }}>
        CometChat Error: {error}
      </div>
    );
  }

  if (!isReady) {
    return null; // Or a loading spinner
  }

  return (
    <CometChatContext.Provider value={{ isReady, error }}>
      {children}
    </CometChatContext.Provider>
  );
}
```

### Usage

```typescript
// In your app layout or route wrapper:
<CometChatProvider
  appId={import.meta.env.VITE_COMETCHAT_APP_ID}
  region={import.meta.env.VITE_COMETCHAT_REGION}
  authKey={import.meta.env.VITE_COMETCHAT_AUTH_KEY}
  // Optional — wire your analytics on each lifecycle event (ENG-35715):
  telemetry={(event) => {
    if (event.phase === "init_finished" || event.phase === "login_finished") {
      analytics.track(`cometchat.${event.phase}`, { ms: event.durationMs });
    } else if (event.phase === "init_failed" || event.phase === "login_failed") {
      analytics.trackError(`cometchat.${event.phase}`, { error: String(event.error) });
    } else {
      analytics.track(`cometchat.${event.phase}`, event);
    }
  }}
>
  <ChatPage />
</CometChatProvider>
```

The provider pattern keeps init/login logic in one place. Chat components inside `<CometChatProvider>` are guaranteed to render only after init and login succeed.

### Pretty-print errors — DO NOT `String(error)` (ENG-35719)

`CometChat.CometChatException` objects look like `{ code: "ERROR_API_KEY_NOT_FOUND", message: "Auth Key cannot be empty", details: ..., source: ... }` (in some kit versions the fields are `errorCode` / `errorDescription`). Calling `String(e)` on them yields `"[object Object]"` — the integrator then has to open devtools, copy the error to the console, and `JSON.stringify` it by hand just to read the message. Testers consistently flag this as the most frustrating moment of the first-run integration.

**Emit this helper in `cometchat/errors.ts` and reuse it from the provider, login screen, and any feature module that catches a kit error:**

```typescript
// cometchat/errors.ts
export function formatCometChatError(e: unknown): string {
  if (e == null) return "Unknown CometChat error.";
  const err = e as Record<string, unknown>;
  const code =
    (err.code as string | undefined) ??
    (err.errorCode as string | undefined);
  const message =
    (err.message as string | undefined) ??
    (err.errorDescription as string | undefined);
  if (code && message) return `[CometChat ${code}] ${message}`;
  if (message) return `[CometChat] ${message}`;
  try {
    return `[CometChat] ${JSON.stringify(e)}`;
  } catch {
    return `[CometChat] ${String(e)}`;
  }
}

const KNOWN_DOC_HINTS: Record<string, string> = {
  ERROR_API_KEY_NOT_FOUND:
    "Auth Key is missing or invalid. Check your env vars (VITE_COMETCHAT_AUTH_KEY / EXPO_PUBLIC_COMETCHAT_AUTH_KEY) and confirm the key in Dashboard → App → Credentials.",
  ERR_UID_NOT_FOUND:
    "The UID you're logging in with doesn't exist in this CometChat app. Create the user in Dashboard → Users, or pick one of the pre-seeded test UIDs (cometchat-uid-1 .. cometchat-uid-5).",
  ERR_AUTH_TOKEN_NOT_FOUND:
    "Auth token is empty or expired. Re-mint it from your backend via the CometChat REST API.",
  AUTH_ERR_BOT:
    "This UID is flagged as a Bot in the dashboard — auth-key login is refused for bot users by design. Toggle Bot OFF in Dashboard → Users, or pick a non-bot UID.",
};

export function logCometChatError(e: unknown): void {
  const formatted = formatCometChatError(e);
  console.error(formatted, e);
  const code = (e as { code?: string; errorCode?: string })?.code ??
               (e as { code?: string; errorCode?: string })?.errorCode;
  if (code && KNOWN_DOC_HINTS[code]) {
    console.warn(`[CometChat hint] ${KNOWN_DOC_HINTS[code]}`);
  }
}
```

Then in the provider:

```typescript
} catch (e) {
  logCometChatError(e);
  setError(formatCometChatError(e));
}
```

And in the error renderer:

```tsx
if (error) {
  return (
    <div role="alert" style={{ color: "#b91c1c", padding: 16, fontFamily: "ui-monospace, monospace", whiteSpace: "pre-wrap" }}>
      <strong>CometChat failed to initialize.</strong>
      <div style={{ marginTop: 8 }}>{error}</div>
      <div style={{ marginTop: 8, fontSize: 12, opacity: 0.7 }}>
        See the browser console for the full error object and any [CometChat hint] line above it.
      </div>
    </div>
  );
}
```

This three-part recipe — `formatCometChatError` for the visible message, `logCometChatError` for the console (with a docs hint for known codes), and a multi-line render that points at the console — turns "ERR_API_KEY_NOT_FOUND" from a 10-minute debugging session into a 10-second fix.

> ⚠️ **Replace `setError(String(e))` everywhere.** The two earlier examples in this skill (§1 init-in-useEffect, §6 provider's setup() catch) use `setError(String(e))` for compactness — when you scaffold the real integration, emit `formatCometChatError(e)` instead and import it from `cometchat/errors.ts`. The same applies to RN (`cometchat-native-core`), Angular (`cometchat-angular-core`), and the native cores — the helper is platform-agnostic, just adapt the file extension.

---

## 7. RTL, i18n, and accessibility

These three concerns share one property: the UI Kit handles them out of the box, but a careless customization can break them. Read this before writing custom views, composer actions, or header replacements.

### RTL (right-to-left)

The UI Kit reads `dir="rtl"` from the document root. If the project already sets `<html dir="rtl">` (or toggles it dynamically for Arabic/Hebrew locales), **CometChat components flip automatically** — message bubbles mirror, avatars swap sides, icons rotate where appropriate. No CometChat-specific config needed.

**To test:** add `<html dir="rtl">` to `index.html` (or set it via JS in Next.js App Router: `<html dir="rtl">` in `app/layout.tsx`). Reload — the conversation list avatar + text should render on the right, message bubbles mirror, the composer input aligns right.

**When customizing:** if you replace a default view (e.g. a custom message bubble), test it in both LTR and RTL. The UI Kit's components use logical properties (`margin-inline-start`, `padding-inline-end`) — your custom components should too, or they'll break RTL.

### i18n (translations)

The UI Kit has a built-in `CometChatLocalize` utility that covers ~40 languages out of the box. Initialize it once, alongside `CometChatUIKit.init()`:

```typescript
import { CometChatLocalize } from "@cometchat/chat-uikit-react";

CometChatLocalize.init({
  language: "es",  // or "fr", "de", "ar", "hi", etc.
});
```

For a dynamic language switcher, call `CometChatLocalize.setCurrentLanguage(newLang)` when the user picks a language (NOT `setLocale` — that method doesn't exist in v6). The UI Kit re-renders with the new strings.

**To override a string:** there's no nested `resources: { en: {...} }` option. Use either `translationsForLanguage` at init (a FLAT key→value map for the chosen `language`), or the standalone `CometChatLocalize.addTranslation({...})`:

```typescript
// (a) at init — flat map for the active language
CometChatLocalize.init({
  language: "en",
  translationsForLanguage: {
    "type a message": "Write your message…",
    "start a conversation": "Say hi 👋",
  },
});

// (b) anytime after init
CometChatLocalize.addTranslation({
  "type a message": "Write your message…",
});
```

**Full translation key list** lives under `node_modules/@cometchat/chat-uikit-react/dist/types/resources/` (types) or the docs MCP. Don't invent keys — unknown keys fall through to the default.

### Accessibility

Default components ship with:
- `aria-label` on icon-only buttons (send, attach, call, etc.)
- `role="listbox"` + `role="option"` on conversation / user / group lists
- Keyboard navigation: `Tab` to focus, `Enter` to activate, `Esc` to close modals
- Focus management: opening a thread view moves focus to the thread header; closing returns focus to the trigger

**Rules when customizing:**

1. **Replacing an icon-only button?** Add `aria-label="<verb>"` (e.g. `aria-label="Send message"`).
2. **Replacing a list item?** Keep `role="option"` + `aria-selected` on the wrapping element.
3. **Replacing the composer?** Preserve the `<textarea>` with an accessible `<label>` (visible or `aria-label`), and keep `Enter`/`Shift+Enter` behavior.
4. **Replacing a modal?** Trap focus inside the modal while open, restore focus to the trigger on close, and add `role="dialog"` + `aria-modal="true"` + a labelled heading.
5. **Color contrast:** when theming with custom colors, verify text contrast ≥ 4.5:1 against background. A low-saturation primary color on a white background breaks AA contrast.

For deep customization (e.g. a fully custom message bubble), the a11y responsibility shifts to the custom component — the UI Kit only guarantees it for its own defaults. Test with a screen reader (VoiceOver on macOS, NVDA on Windows) and keyboard-only navigation before shipping.

---

## 8. Anti-patterns

These are specific things NOT to do. Each one causes real bugs that are hard to debug.

1. **Do NOT call `CometChatUIKit.init()` during render.** Init is async and has side effects. Calling it during render causes infinite re-render loops. Always call in `useEffect` or before `createRoot`.

2. **Do NOT import `css-variables.css` in multiple files.** Duplicate imports cause CSS specificity conflicts and doubled variable declarations. Import it exactly once at the app root.

3. **Do NOT render CometChat components before init completes.** Components assume the SDK is initialized. Rendering before init finishes causes "CometChat is not initialized" runtime errors. Use the provider pattern or a ready-state gate.

4. **Do NOT hardcode `AUTH_KEY` in source files.** The auth key is a secret. Use environment variables during development. Use auth tokens in production.

5. **Guard concurrent `login()` calls with a module-level in-flight promise.** `login()` is only safe to call sequentially. Two `login()` calls overlapping (e.g. React 18 StrictMode's double effect) throw *"Please wait until the previous login request ends."* Cache the first login's promise at module scope and `await` that from subsequent callers. See the `ensureLoggedIn` helper in section 2 and section 6's provider pattern.

6. **Do NOT render CometChat components in a server-side context.** All components require browser APIs. In Next.js, always use `"use client"`. In Astro, always use `client:only="react"`.

7. **Do NOT target CometChat's internal CSS class names for styling.** These are not part of the public API. Use `--cometchat-*` CSS variables instead. Internal classes change between minor versions.

8. **Do NOT create CometChat components without a container that has explicit dimensions.** CometChat components fill 100% of their container. If the container has no height, the components collapse to zero height. Always set `height`, `min-height`, or use flexbox/grid to give the container dimensions.

9. **Do NOT re-initialize CometChat when navigating between routes.** Init should happen once at the app level (in the provider or entry file), not per-route. Re-initializing causes flickering and dropped WebSocket connections.

10. **Do NOT invent component names.** CometChat exports specific components with specific names. Check the `cometchat-components` skill before writing any `<CometChat*>` JSX. Using a wrong name (e.g., `<CometChatChat>`, `<CometChatMessenger>`) causes a build error.

11. **Do NOT wrap CometChat components in a `transform`ed container.** Per the CSS spec, any non-`none` `transform` on an element creates a new containing block for `position: fixed` descendants. CometChat UI Kit renders several overlays as `position: fixed` (message options menu, emoji picker, file preview, reactions popover, thread panel) and expects them to anchor to the viewport. Wrapping the chat in a container that uses `transform: translateX(...)` — a common pattern for slide-in drawers / sidebars — reparents those overlays to the drawer, causing them to appear clipped, offset, or drift mid-animation.

    **This includes Tailwind's `translate-x-*` utilities — `translate-x-full`, `-translate-x-full`, `translate-x-0`, `translate-x-[420px]`, etc. all compile to `transform: translateX(...)` and trigger the same bug.** Same for `-translate-y-*`, `translate-*`, `scale-*`, `rotate-*`, `skew-*`, `transform-*`, and any `transition-transform` utility applied to a container wrapping CometChat components. If you see yourself reaching for any Tailwind class in the `transform:` family on a drawer/sidebar/modal that contains chat UI, stop.

    **Animate the `right` / `left` offset instead**, or use `margin-right: isOpen ? 0 : -<width>`. In Tailwind: toggle between `right-0` and a negative `right-[-420px]` with `transition-[right]` instead of `transition-transform`.

    Same rule applies to `filter`, `perspective`, `backdrop-filter`, and `will-change: transform` — any of those also trigger the containing-block takeover. See `cometchat-placement`'s drawer and widget patterns for the correct right-offset animation.

---

## 9. Docs MCP (recommended, not required)

The CometChat docs MCP provides runtime access to the latest documentation, including prop types, callback signatures, request builder methods, SDK events, CSS variable names, and error decoders.

### Installation

```bash
claude mcp add --transport http cometchat-docs https://www.cometchat.com/docs/mcp
```

For other clients, see: https://www.cometchat.com/docs/mcp-server

### When to use

- Looking up a prop's exact type or default value
- Finding callback signatures (e.g., what `onItemClick` passes)
- Checking request builder methods (e.g., `ConversationsRequestBuilder.setLimit`)
- Understanding SDK events (e.g., `CometChatMessageEvents.ccMessageSent`)
- Verifying CSS variable names before writing overrides
- Decoding error messages (e.g., "INVALID_AUTH_KEY")

### When NOT to use

- For component names and basic props -- use the `cometchat-components` skill instead (it works offline)
- For init/login/CSS patterns -- they are in this skill
- For placement patterns -- they are in the `cometchat-placement` skill
- For anything the CLI handles -- the CLI templates are the source of truth for those paths

##

…(truncated)