diff --git a/middleware/src/idempotency/idempotency.config.ts b/middleware/src/idempotency/idempotency.config.ts
new file mode 100644
index 00000000..df590c17
--- /dev/null
+++ b/middleware/src/idempotency/idempotency.config.ts
@@ -0,0 +1,9 @@
+export const IDEMPOTENCY_CONFIG = {
+  ttl: {
+    puzzleSubmission: 300, // 5 minutes
+    pointClaim: 600,       // 10 minutes
+    friendRequest: 3600,   // 1 hour
+    profileUpdate: 60,     // 1 minute
+  },
+  headerKey: 'x-idempotency-key',
+};
diff --git a/middleware/src/idempotency/idempotency.middleware.ts b/middleware/src/idempotency/idempotency.middleware.ts
new file mode 100644
index 00000000..fa7e3cc4
--- /dev/null
+++ b/middleware/src/idempotency/idempotency.middleware.ts
@@ -0,0 +1,56 @@
+import { Injectable, NestMiddleware, BadRequestException } from '@nestjs/common';
+import { Request, Response, NextFunction } from 'express';
+import { IdempotencyService } from './idempotency.service';
+import { IDEMPOTENCY_CONFIG } from './idempotency.config';
+
+@Injectable()
+export class IdempotencyMiddleware implements NestMiddleware {
+  constructor(private readonly idempotencyService: IdempotencyService) {}
+
+  async use(req: Request, res: Response, next: NextFunction) {
+    // Skip GET requests
+    if (req.method === 'GET') return next();
+
+    const headerKey = IDEMPOTENCY_CONFIG.headerKey;
+    let idempotencyKey = req.headers[headerKey] as string;
+
+    if (!idempotencyKey) {
+      // Auto-generate key if not provided
+      idempotencyKey = await this.idempotencyService.generateKey(req);
+    }
+
+    if (typeof idempotencyKey !== 'string') {
+      throw new BadRequestException('Invalid idempotency key format');
+    }
+
+    const cachedResponse = await this.idempotencyService.getResponse(idempotencyKey);
+    if (cachedResponse) {
+      // Return cached response immediately
+      res.set(cachedResponse.headers);
+      return res.status(cachedResponse.statusCode).send(cachedResponse.body);
+    }
+
+    // Intercept response to store it
+    const originalSend = res.send.bind(res);
+    res.send = async (body: any) => {
+      const ttl = this.resolveTTL(req.originalUrl);
+      const responsePayload = {
+        statusCode: res.statusCode,
+        headers: res.getHeaders(),
+        body,
+      };
+      await this.idempotencyService.storeResponse(idempotencyKey, responsePayload, ttl);
+      return originalSend(body);
+    };
+
+    next();
+  }
+
+  private resolveTTL(url: string): number {
+    if (url.includes('/puzzles')) return IDEMPOTENCY_CONFIG.ttl.puzzleSubmission;
+    if (url.includes('/points')) return IDEMPOTENCY_CONFIG.ttl.pointClaim;
+    if (url.includes('/friends')) return IDEMPOTENCY_CONFIG.ttl.friendRequest;
+    if (url.includes('/profile')) return IDEMPOTENCY_CONFIG.ttl.profileUpdate;
+    return 300; // default
+  }
+}
diff --git a/middleware/src/idempotency/idempotency.service.ts b/middleware/src/idempotency/idempotency.service.ts
new file mode 100644
index 00000000..fc2d410a
--- /dev/null
+++ b/middleware/src/idempotency/idempotency.service.ts
@@ -0,0 +1,25 @@
+import { Injectable } from '@nestjs/common';
+import { RedisService } from '../../redis/redis.service';
+import * as crypto from 'crypto';
+
+@Injectable()
+export class IdempotencyService {
+  constructor(private readonly redisService: RedisService) {}
+
+  async generateKey(req: any): Promise<string> {
+    const userId = req.user?.id || 'anon';
+    const bodyHash = crypto.createHash('sha256').update(JSON.stringify(req.body)).digest('hex');
+    return `${userId}:${req.method}:${req.originalUrl}:${bodyHash}`;
+  }
+
+  async storeResponse(key: string, response: any, ttl: number) {
+    const client = this.redisService.getClient();
+    await client.set(key, JSON.stringify(response), 'EX', ttl, 'NX'); // SETNX for atomicity
+  }
+
+  async getResponse(key: string): Promise<any | null> {
+    const client = this.redisService.getClient();
+    const data = await client.get(key);
+    return data ? JSON.parse(data) : null;
+  }
+}
diff --git a/middleware/src/transaction/transaction.logger.ts b/middleware/src/transaction/transaction.logger.ts
new file mode 100644
index 00000000..2e923098
--- /dev/null
+++ b/middleware/src/transaction/transaction.logger.ts
@@ -0,0 +1,14 @@
+import { Injectable, Logger } from '@nestjs/common';
+
+@Injectable()
+export class TransactionLogger {
+  private readonly logger = new Logger('Transaction');
+
+  log(message: string) {
+    this.logger.log(message);
+  }
+
+  error(message: string, error: any) {
+    this.logger.error(`${message}: ${error.message}`, error.stack);
+  }
+}
diff --git a/middleware/src/transaction/transaction.manager.ts b/middleware/src/transaction/transaction.manager.ts
new file mode 100644
index 00000000..8175ec7b
--- /dev/null
+++ b/middleware/src/transaction/transaction.manager.ts
@@ -0,0 +1,36 @@
+import { DataSource, QueryRunner } from 'typeorm';
+
+export class TransactionManager {
+  private queryRunner: QueryRunner;
+
+  constructor(private readonly dataSource: DataSource) {
+    this.queryRunner = this.dataSource.createQueryRunner();
+  }
+
+  async startTransaction(isolation: 'READ COMMITTED' | 'REPEATABLE READ' | 'SERIALIZABLE' = 'READ COMMITTED') {
+    await this.queryRunner.connect();
+    await this.queryRunner.startTransaction(isolation);
+  }
+
+  async commitTransaction() {
+    await this.queryRunner.commitTransaction();
+    await this.queryRunner.release();
+  }
+
+  async rollbackTransaction() {
+    await this.queryRunner.rollbackTransaction();
+    await this.queryRunner.release();
+  }
+
+  async createSavepoint(name: string) {
+    await this.queryRunner.query(`SAVEPOINT ${name}`);
+  }
+
+  async rollbackToSavepoint(name: string) {
+    await this.queryRunner.query(`ROLLBACK TO SAVEPOINT ${name}`);
+  }
+
+  getManager() {
+    return this.queryRunner.manager;
+  }
+}
diff --git a/middleware/src/transaction/transaction.middleware.ts b/middleware/src/transaction/transaction.middleware.ts
new file mode 100644
index 00000000..11bb6803
--- /dev/null
+++ b/middleware/src/transaction/transaction.middleware.ts
@@ -0,0 +1,37 @@
+import { Injectable, NestMiddleware } from '@nestjs/common';
+import { Request, Response, NextFunction } from 'express';
+import { DataSource } from 'typeorm';
+import { TransactionManager } from './transaction.manager';
+import { TransactionLogger } from './transaction.logger';
+
+@Injectable()
+export class TransactionMiddleware implements NestMiddleware {
+  constructor(private readonly dataSource: DataSource, private readonly logger: TransactionLogger) {}
+
+  async use(req: Request, res: Response, next: NextFunction) {
+    const manager = new TransactionManager(this.dataSource);
+
+    try {
+      await manager.startTransaction();
+
+      // Attach transaction manager to request for manual control if needed
+      (req as any).transactionManager = manager;
+
+      res.on('finish', async () => {
+        if (res.statusCode >= 200 && res.statusCode < 400) {
+          await manager.commitTransaction();
+          this.logger.log('Transaction committed successfully');
+        } else {
+          await manager.rollbackTransaction();
+          this.logger.log('Transaction rolled back due to error');
+        }
+      });
+
+      next();
+    } catch (error) {
+      await manager.rollbackTransaction();
+      this.logger.error('Transaction failed', error);
+      next(error);
+    }
+  }
+}