diff --git a/src/app.ts b/src/app.ts
new file mode 100644
index 0000000..cf970b5
--- /dev/null
+++ b/src/app.ts
@@ -0,0 +1,76 @@
+import Fastify, { FastifyInstance } from 'fastify';
+import { AppError } from './utils/errors.js';
+import databasePlugin from './plugins/database.js';
+import redisPlugin from './plugins/redis.js';
+import securityPlugin from './plugins/security.js';
+import rateLimitPlugin from './plugins/rateLimit.js';
+import { env } from './config/env.js';
+import { randomUUID } from 'node:crypto';
+
+export async function buildApp(): Promise<FastifyInstance> {
+  const isDev = env.NODE_ENV === 'development';
+
+  const app = Fastify({
+    logger: {
+      level: isDev ? 'debug' : 'info',
+      transport:
+        isDev
+          ? {
+              target: 'pino-pretty',
+              options: {
+                translateTime: 'HH:MM:ss Z',
+                ignore: 'pid,hostname',
+              },
+            }
+          : undefined,
+    },
+    requestIdHeader: 'x-request-id',
+    requestIdLogLabel: 'requestId',
+    genReqId: () => randomUUID(),
+  });
+
+  app.setErrorHandler((err: unknown, request, reply) => {
+    const error = err as Error & { statusCode?: number; validation?: unknown };
+    request.log.error({ err }, error.message);
+
+    if (err instanceof AppError) {
+      const statusCode = err.statusCode;
+      const payload = err.toJSON();
+      if (err.code === 'RATE_LIMIT_EXCEEDED' && 'retryAfter' in err) {
+        reply.header('Retry-After', String((err as AppError & { retryAfter?: number }).retryAfter ?? 60));
+      }
+      return reply.status(statusCode).send(payload);
+    }
+
+    if (error.validation) {
+      return reply.status(422).send({
+        error: {
+          code: 'VALIDATION_ERROR',
+          message: 'Validation failed',
+          details: error.validation,
+        },
+      });
+    }
+
+    const statusCode = error.statusCode ?? 500;
+    return reply.status(statusCode).send({
+      error: {
+        code: 'INTERNAL_ERROR',
+        message: env.NODE_ENV === 'production' ? 'Internal server error' : error.message,
+      },
+    });
+  });
+
+  app.addHook('onRequest', async (request, reply) => {
+    reply.header('x-request-id', request.id);
+  });
+
+  await app.register(redisPlugin);
+  await app.register(databasePlugin);
+  await app.register(securityPlugin);
+  await app.register(rateLimitPlugin);
+
+  app.get('/health', async () => ({ status: 'ok', timestamp: new Date().toISOString() }));
+
+  return app;
+}