diff --git a/client/lib/mock-auth.ts b/client/lib/mock-auth.ts
new file mode 100644
index 00000000..1bdc468f
--- /dev/null
+++ b/client/lib/mock-auth.ts
@@ -0,0 +1,161 @@
+// Mock authentication service for development when Supabase is not available
+interface MockUser {
+  id: string;
+  email: string;
+  created_at: string;
+}
+
+interface MockSession {
+  user: MockUser;
+  access_token: string;
+}
+
+interface MockProfile {
+  id: string;
+  username: string;
+  email: string;
+  role: string;
+  onboarded: boolean;
+  full_name?: string;
+  bio?: string;
+  level: number;
+  total_xp: number;
+  avatar_url?: string;
+  created_at: string;
+  updated_at: string;
+}
+
+class MockAuthService {
+  private currentUser: MockUser | null = null;
+  private currentSession: MockSession | null = null;
+  private profiles: Map<string, MockProfile> = new Map();
+
+  constructor() {
+    // Load from localStorage if available
+    const savedUser = localStorage.getItem('mock_user');
+    const savedProfile = localStorage.getItem('mock_profile');
+    
+    if (savedUser) {
+      this.currentUser = JSON.parse(savedUser);
+      if (this.currentUser) {
+        this.currentSession = {
+          user: this.currentUser,
+          access_token: 'mock_token_' + Date.now()
+        };
+      }
+    }
+    
+    if (savedProfile) {
+      const profile = JSON.parse(savedProfile);
+      this.profiles.set(profile.id, profile);
+    }
+  }
+
+  async signInWithPassword(email: string, password: string) {
+    // Mock validation - accept any email/password for demo
+    if (!email || !password) {
+      throw new Error('Email and password are required');
+    }
+
+    const user: MockUser = {
+      id: 'mock_user_' + email.replace(/[^a-z0-9]/gi, '_'),
+      email,
+      created_at: new Date().toISOString()
+    };
+
+    this.currentUser = user;
+    this.currentSession = {
+      user,
+      access_token: 'mock_token_' + Date.now()
+    };
+
+    // Save to localStorage
+    localStorage.setItem('mock_user', JSON.stringify(user));
+
+    return {
+      data: {
+        user,
+        session: this.currentSession
+      },
+      error: null
+    };
+  }
+
+  async signOut() {
+    this.currentUser = null;
+    this.currentSession = null;
+    localStorage.removeItem('mock_user');
+    localStorage.removeItem('mock_profile');
+    
+    return { error: null };
+  }
+
+  async getUser() {
+    return {
+      data: { user: this.currentUser },
+      error: null
+    };
+  }
+
+  async getSession() {
+    return {
+      data: { session: this.currentSession },
+      error: null
+    };
+  }
+
+  // Mock database operations
+  async getUserProfile(userId: string): Promise<MockProfile | null> {
+    return this.profiles.get(userId) || null;
+  }
+
+  async updateProfile(userId: string, updates: Partial<MockProfile>): Promise<MockProfile> {
+    let profile = this.profiles.get(userId);
+    
+    if (!profile) {
+      // Create new profile
+      profile = {
+        id: userId,
+        username: updates.username || this.currentUser?.email?.split('@')[0] || 'user',
+        email: this.currentUser?.email || '',
+        role: 'member',
+        onboarded: true,
+        level: 1,
+        total_xp: 0,
+        created_at: new Date().toISOString(),
+        updated_at: new Date().toISOString(),
+        ...updates
+      };
+    } else {
+      // Update existing
+      profile = {
+        ...profile,
+        ...updates,
+        updated_at: new Date().toISOString()
+      };
+    }
+
+    this.profiles.set(userId, profile);
+    localStorage.setItem('mock_profile', JSON.stringify(profile));
+    
+    return profile;
+  }
+
+  onAuthStateChange(callback: (event: string, session: MockSession | null) => void) {
+    // Immediately call with current state
+    setTimeout(() => {
+      callback(this.currentSession ? 'SIGNED_IN' : 'SIGNED_OUT', this.currentSession);
+    }, 100);
+
+    // Return unsubscribe function
+    return {
+      data: {
+        subscription: {
+          unsubscribe: () => {}
+        }
+      }
+    };
+  }
+}
+
+export const mockAuth = new MockAuthService();