feat: centralize XP magic numbers in config file with shared level formula

app/src/sections/DailyChallenges.tsx

@@ -15,6 +15,7 @@ import { getAllProblems } from '@/api/content';
 import { updateProblemStatus, getUserProgress } from '@/api/userActions';
 import { useAuth } from '@/contexts/AuthContext';
 import { toast } from 'sonner';
+import { SOLVE_XP } from '@/utils/xpConfig';
 
 interface DailyChallengesProps {
     onBack: () => void;
@@ -140,7 +141,7 @@ export function DailyChallenges({ onBack }: DailyChallengesProps) {
 
         try {
             await updateProblemStatus(problemMongoId, wasCompleted ? 'TODO' : 'SOLVED');
-            if (!wasCompleted) toast.success('Challenge problem solved! +25 XP');
+            if (!wasCompleted) toast.success(`Challenge problem solved! +${SOLVE_XP} XP`);
             refreshProfile();
         } catch {
             setCompletedProblems(prev => {
@@ -205,7 +206,7 @@ export function DailyChallenges({ onBack }: DailyChallengesProps) {
                         </div>
                         <div className="flex items-center gap-2 px-4 py-2 rounded-full glass">
                             <Zap className="w-5 h-5 text-[#ffd700]" />
-                            <span className="text-white font-medium">{challengesSolved * 25} XP Earned</span>
+                            <span className="text-white font-medium">{challengesSolved * SOLVE_XP} XP Earned</span>
                         </div>
                     </div>
                 </motion.div>
@@ -309,7 +310,7 @@ export function DailyChallenges({ onBack }: DailyChallengesProps) {
                                 <div className="flex items-center gap-2 mt-3 pt-3 border-t border-white/5">
                                     <Zap className="w-4 h-4 text-[#ffd700]" />
                                     <span className="text-sm text-white/40">
-                                        {isCompleted ? 'Earned' : 'Reward'}: <span className="text-[#ffd700]">+25 XP</span>
+                                        {isCompleted ? 'Earned' : 'Reward'}: <span className="text-[#ffd700]">+{SOLVE_XP} XP</span>
                                     </span>
                                 </div>
                             </motion.div>

app/src/sections/Dashboard.tsx

@@ -23,6 +23,7 @@ import {
 import { useAuth } from '@/contexts/AuthContext';
 import { getAllProblems, getAllTopics } from '@/api/content';
 import { getUserProgress, getDashboardStats } from '@/api/userActions';
+import { SOLVE_XP, XP_PER_LEVEL, calculateLevel } from '@/utils/xpConfig';
 
 interface DashboardProps {
   onNavigate: (view: 'home' | 'dashboard' | 'topic' | 'problems' | 'notes' | 'leaderboard' | 'daily-challenges', topicId?: string) => void;
@@ -140,7 +141,7 @@ export function Dashboard({ onNavigate }: DashboardProps) {
 
     const totalSolved = solvedIds.size;
     const totalProblems = problems.length;
-    const xpPoints = profile?.xp_points ?? totalSolved * 25;
+    const xpPoints = profile?.xp_points ?? totalSolved * SOLVE_XP;
 
     let easy = 0, medium = 0, hard = 0;
     let easyTotal = 0, mediumTotal = 0, hardTotal = 0;
@@ -281,7 +282,7 @@ export function Dashboard({ onNavigate }: DashboardProps) {
     return { x: cx + r * Math.cos(rad), y: cy + r * Math.sin(rad) };
   }
 
-  const level = Math.floor((stats.xpPoints) / 1000) + 1;
+  const level = calculateLevel(stats.xpPoints);
 
   if (loading) {
     return (
@@ -407,6 +408,8 @@ export function Dashboard({ onNavigate }: DashboardProps) {
         >
           {[
             { label: 'Problems Solved', value: animSolved, sub: `of ${stats.totalProblems}`, icon: CheckCircle2, color: '#a088ff', glow: 'rgba(160,136,255,0.15)' },
+            { label: 'XP Points', value: animXP, sub: `Level ${level}`, icon: Zap, color: '#ffd700', glow: 'rgba(255,215,0,0.12)', tooltip: `Earn ${SOLVE_XP} XP per solved problem. Every ${XP_PER_LEVEL.toLocaleString()} XP = 1 Level.` },
+            { label: 'Day Streak', value: animStreak, sub: stats.currentStreak > 0 ? 'Keep it up!' : 'Solve to start!', icon: Flame, color: '#ff8a63', glow: 'rgba(255,138,99,0.12)' },
             { label: 'XP Points', value: animXP, sub: `Level ${level}`, icon: Zap, color: '#ffd700', glow: 'rgba(255,215,0,0.12)' },
             { label: 'Day Streak', value: animStreak, sub: 'Resets at midnight UTC', icon: Flame, color: '#ff8a63', glow: 'rgba(255,138,99,0.12)' },
             { label: 'Global Rank', value: `#${rankInfo.rank}`, sub: `Top ${rankInfo.topPercent}%`, icon: Trophy, color: '#88ff9f', glow: 'rgba(136,255,159,0.12)' },
@@ -416,7 +419,17 @@ export function Dashboard({ onNavigate }: DashboardProps) {
               whileHover={{ scale: 1.03, y: -4 }}
               transition={{ type: 'spring', stiffness: 400, damping: 25 }}
               className="relative glass rounded-2xl p-5 overflow-hidden group cursor-default"
+              role="status"
+              aria-label={`${stat.label}: ${stat.value}`}
             >
+              {stat.tooltip && (
+                <div className="absolute top-2 right-2 z-20">
+                  <div className="relative group/tooltip">
+                    <div className="w-4 h-4 rounded-full bg-white/10 flex items-center justify-center text-[10px] text-white/40 cursor-help">?</div>
+                    <div className="absolute bottom-full right-0 mb-2 w-48 p-2 rounded-lg bg-[#1e1e2d] border border-white/10 text-xs text-white/70 opacity-0 group-hover/tooltip:opacity-100 transition-opacity pointer-events-none z-30">
+                      {stat.tooltip}
+                    </div>
+                  </div>
               {isRefreshing && (
                 <div className="absolute inset-0 bg-white/5 backdrop-blur-sm flex items-center justify-center z-10 rounded-2xl">
                   <RefreshCw className="w-5 h-5 text-white/50 animate-spin" />
@@ -831,7 +844,7 @@ export function Dashboard({ onNavigate }: DashboardProps) {
                           </div>
                         </div>
                       </div>
-                      <span className="text-xs font-medium text-[#88ff9f]/70">+25 XP</span>
+                      <span className="text-xs font-medium text-[#88ff9f]/70">+{SOLVE_XP} XP</span>
                     </motion.div>
                   );
                 }) : (

app/src/sections/Problems.tsx

@@ -22,6 +22,7 @@ import { updateProblemStatus, toggleBookmark as apiToggleBookmark, getUserProgre
 import { useAuth } from '@/contexts/AuthContext';
 import { Input } from '@/components/ui/input';
 import { toast } from 'sonner';
+import { SOLVE_XP } from '@/utils/xpConfig';
 
 export function Problems() {
   const { data: problemsData = [], isLoading: problemsLoading } = useQuery({
@@ -125,7 +126,7 @@ export function Problems() {
 
     try {
       await updateProblemStatus(problemMongoId, wasCompleted ? 'TODO' : 'SOLVED');
-      if (!wasCompleted) toast.success('Problem marked as complete! +25 XP');
+      if (!wasCompleted) toast.success(`Problem marked as complete! +${SOLVE_XP} XP`);
       // Refresh profile so nav XP updates immediately
       refreshProfile();
     } catch (e) {

app/src/sections/TopicDetail.tsx

@@ -18,6 +18,7 @@ import { updateProblemStatus, toggleBookmark as apiToggleBookmark, getUserProgre
 import { useAuth } from '@/contexts/AuthContext';
 import { Input } from '@/components/ui/input';
 import { toast } from 'sonner';
+import { SOLVE_XP } from '@/utils/xpConfig';
 
 interface TopicDetailProps {
   topicId: string;
@@ -126,7 +127,7 @@ export function TopicDetail({ topicId, onBack }: TopicDetailProps) {
 
     try {
       await updateProblemStatus(problemMongoId, wasCompleted ? 'TODO' : 'SOLVED');
-      if (!wasCompleted) toast.success('Problem marked as complete! +25 XP');
+      if (!wasCompleted) toast.success(`Problem marked as complete! +${SOLVE_XP} XP`);
       // Refresh profile so nav XP updates immediately
       refreshProfile();
     } catch (e) {

app/src/utils/xpConfig.ts

@@ -0,0 +1,20 @@
+/**
+ * XP and Level Configuration
+ *
+ * Central source of truth for all XP values and level calculations.
+ * Change these values once — they propagate everywhere.
+ */
+
+/** XP awarded for solving a problem */
+export const SOLVE_XP = 25;
+
+/** XP required per level */
+export const XP_PER_LEVEL = 1000;
+
+/**
+ * Calculate a user's level from their total XP.
+ * Formula: level = floor(xp / XP_PER_LEVEL) + 1
+ */
+export function calculateLevel(xpPoints: number): number {
+  return Math.floor(xpPoints / XP_PER_LEVEL) + 1;
+}

backend/src/config/xpConfig.ts

@@ -0,0 +1,20 @@
+/**
+ * XP and Level Configuration
+ *
+ * Central source of truth for all XP values and level calculations.
+ * Change these values once — they propagate everywhere.
+ */
+
+/** XP awarded for solving a problem */
+export const SOLVE_XP = 25;
+
+/** XP required per level */
+export const XP_PER_LEVEL = 1000;
+
+/**
+ * Calculate a user's level from their total XP.
+ * Formula: level = floor(xp / XP_PER_LEVEL) + 1
+ */
+export function calculateLevel(xpPoints: number): number {
+  return Math.floor(xpPoints / XP_PER_LEVEL) + 1;
+}

backend/src/controllers/userActionController.ts

@@ -1,5 +1,6 @@
 import { Request, Response } from 'express';
 import { prisma } from '../config/db';
+import { SOLVE_XP } from '../config/xpConfig';
 
 export const updateProblemStatus = async (req: Request | any, res: Response) => {
     try {
@@ -75,7 +76,7 @@ export const updateProblemStatus = async (req: Request | any, res: Response) =>
                 await prisma.user.update({
                     where: { id: userId },
                     data: {
-                        xp_points: { increment: 25 },
+                        xp_points: { increment: SOLVE_XP },
                         solvedProblems: { push: [{ problemId, solvedAt: today }] },
                         streak_days: newStreak,
                         last_active: today,
@@ -90,7 +91,7 @@ export const updateProblemStatus = async (req: Request | any, res: Response) =>
                 await prisma.user.update({
                     where: { id: userId },
                     data: {
-                        xp_points: { decrement: 25 },
+                        xp_points: { decrement: SOLVE_XP },
                         solvedProblems: updatedSolvedProblems
                     }
                 });

backend/src/controllers/userController.ts

@@ -1,5 +1,6 @@
 import { Request, Response } from 'express';
 import { prisma } from '../config/db';
+import { calculateLevel } from '../config/xpConfig';
 
 // @desc    Get leaderboard data
 // @route   GET /api/users/leaderboard
@@ -148,7 +149,7 @@ export const getUserProfile = async (req: Request, res: Response) => {
             xp: user.xp_points || 0,
             streak: user.streak_days || 0,
             solved: user.solvedProblems?.length || 0,
-            level: Math.floor((user.xp_points || 0) / 100) + 1,
+            level: calculateLevel(user.xp_points || 0),
             memberSince: user.createdAt,
         });
     } catch (error) {
@@ -189,7 +190,7 @@ export const updateUserProfile = async (req: Request | any, res: Response) => {
             xp: updatedUser.xp_points,
             streak: updatedUser.streak_days,
             solved: updatedUser.solvedProblems?.length || 0,
-            level: Math.floor((updatedUser.xp_points || 0) / 100) + 1,
+            level: calculateLevel(updatedUser.xp_points || 0),
             memberSince: updatedUser.createdAt,
         });
     } catch (error) {