diff --git a/apps/api/.gitignore b/apps/api/.gitignore
new file mode 100644
index 0000000..34fee9f
--- /dev/null
+++ b/apps/api/.gitignore
@@ -0,0 +1,4 @@
+
+.claude/
+
+.codegraph/
diff --git a/apps/api/package.json b/apps/api/package.json
index 65c4bc6..0995564 100644
--- a/apps/api/package.json
+++ b/apps/api/package.json
@@ -13,11 +13,17 @@
   },
   "dependencies": {
     "@elysiajs/cors": "1.4.2",
+    "@opentelemetry/api": "1.9.1",
+    "@opentelemetry/exporter-prometheus": "0.218.0",
+    "@opentelemetry/instrumentation-http": "0.218.0",
+    "@opentelemetry/sdk-node": "0.218.0",
+    "@opentelemetry/semantic-conventions": "1.41.1",
     "@zeavis/shared": "workspace:*",
     "bcryptjs": "^3.0.3",
     "drizzle-orm": "^0.45.2",
     "elysia": "^1.4.28",
-    "postgres": "^3.4.9"
+    "postgres": "^3.4.9",
+    "prom-client": "15.1.3"
   },
   "devDependencies": {
     "@types/bcryptjs": "^3.0.0",
diff --git a/apps/api/src/index.ts b/apps/api/src/index.ts
index 2d80cc4..91d11be 100644
--- a/apps/api/src/index.ts
+++ b/apps/api/src/index.ts
@@ -9,6 +9,9 @@ import { diagnosisRoutes } from './routes/diagnoses';
 import { dashboardRoutes } from './routes/dashboard';
 import { authRoutes } from './routes/auth';
 import { expertRoutes } from './routes/expert';
+import { metricsRoutes } from './routes/metrics';
+import { httpRequestCounter, httpRequestDuration, httpRequestsActive } from './lib/telemetry';
+import './types';
 
 assertRequiredEnv();
 
@@ -17,6 +20,24 @@ const app = new Elysia()
     origin: env.webAppUrl,
     credentials: true,
   }))
+  .use(metricsRoutes)
+  .onBeforeHandle(({ request, path }) => {
+    httpRequestsActive.inc();
+    request.metricsStart = performance.now();
+    request.metricsPath = path;
+  })
+  .onAfterHandle(({ request, set }) => {
+    const start = (request as any).metricsStart as number | undefined;
+    const path = (request as any).metricsPath as string | undefined;
+    if (start && path) {
+      const duration = (performance.now() - start) / 1000;
+      const method = request.method;
+      const status = set.status ?? 200;
+      httpRequestCounter.labels(method, path, String(status)).inc();
+      httpRequestDuration.labels(method, path).observe(duration);
+    }
+    httpRequestsActive.dec();
+  })
   .use(healthRoutes)
   .use(statusRoutes)
   .use(authRoutes)
diff --git a/apps/api/src/lib/telemetry.ts b/apps/api/src/lib/telemetry.ts
new file mode 100644
index 0000000..cd55a90
--- /dev/null
+++ b/apps/api/src/lib/telemetry.ts
@@ -0,0 +1,62 @@
+import { Registry, Counter, Histogram, Gauge, collectDefaultMetrics } from 'prom-client';
+
+const registry = new Registry();
+
+// Collect default Node.js metrics (CPU, memory, event loop, etc.)
+collectDefaultMetrics({ register: registry });
+
+// ── HTTP Metrics ────────────────────────────────────────
+
+export const httpRequestCounter = new Counter({
+  name: 'zeavis_api_http_requests_total',
+  help: 'Total number of HTTP requests handled by the API',
+  labelNames: ['method', 'path', 'status'] as const,
+  registers: [registry],
+});
+
+export const httpRequestDuration = new Histogram({
+  name: 'zeavis_api_http_request_duration_seconds',
+  help: 'Histogram of HTTP request durations in seconds',
+  labelNames: ['method', 'path'] as const,
+  buckets: [0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5],
+  registers: [registry],
+});
+
+export const httpRequestsActive = new Gauge({
+  name: 'zeavis_api_http_requests_active',
+  help: 'Number of HTTP requests currently being processed',
+  registers: [registry],
+});
+
+// ── Business Metrics ────────────────────────────────────
+
+export const classificationCounter = new Counter({
+  name: 'zeavis_api_classifications_total',
+  help: 'Total number of classification predictions requested via API',
+  labelNames: ['result'] as const,
+  registers: [registry],
+});
+
+export const diagnosisCounter = new Counter({
+  name: 'zeavis_api_diagnoses_total',
+  help: 'Total number of diagnoses created',
+  labelNames: ['disease'] as const,
+  registers: [registry],
+});
+
+export const authCounter = new Counter({
+  name: 'zeavis_api_auth_operations_total',
+  help: 'Total authentication operations (login, register, refresh)',
+  labelNames: ['operation', 'success'] as const,
+  registers: [registry],
+});
+
+// ── Export ──────────────────────────────────────────────
+
+export function getMetricsContentType(): string {
+  return registry.contentType;
+}
+
+export async function getMetrics(): Promise<string> {
+  return await registry.metrics();
+}
diff --git a/apps/api/src/routes/auth.ts b/apps/api/src/routes/auth.ts
index 2d4fc81..770d1e5 100644
--- a/apps/api/src/routes/auth.ts
+++ b/apps/api/src/routes/auth.ts
@@ -16,6 +16,7 @@ import {
   verifyPassword,
 } from '../lib/auth';
 import { env } from '../config/env';
+import { authCounter } from '../lib/telemetry';
 
 function normalizeEmail(email: unknown) {
   return typeof email === 'string' ? email.trim().toLowerCase() : '';
@@ -63,6 +64,8 @@ export const authRoutes = new Elysia({ prefix: '/api/v1/auth' })
       const token = await createSession(user.id);
       set.headers['Set-Cookie'] = createSessionCookie(token);
 
+      authCounter.labels('register', 'true').inc();
+
       return {
         user: {
           id: user.id,
@@ -90,12 +93,15 @@ export const authRoutes = new Elysia({ prefix: '/api/v1/auth' })
       const user = rows[0];
 
       if (!user?.passwordHash || !(await verifyPassword(req!.password!, user.passwordHash))) {
+        authCounter.labels('login', 'false').inc();
         return badRequest('Invalid email or password');
       }
 
       const token = await createSession(user.id);
       set.headers['Set-Cookie'] = createSessionCookie(token);
 
+      authCounter.labels('login', 'true').inc();
+
       return {
         user: {
           id: user.id,
diff --git a/apps/api/src/routes/classifications.ts b/apps/api/src/routes/classifications.ts
index 6f67dc6..b39d943 100644
--- a/apps/api/src/routes/classifications.ts
+++ b/apps/api/src/routes/classifications.ts
@@ -16,6 +16,7 @@ import { desc, eq } from 'drizzle-orm';
 import { classifyImage } from '../lib/image-model';
 import { uploadImageToStorage } from '../lib/uploader-client';
 import { toDisease } from '../lib/disease-mappers';
+import { classificationCounter } from '../lib/telemetry';
 
 function toImageClassificationRecord(row: {
   id: string;
@@ -141,6 +142,8 @@ export const classificationRoutes = new Elysia({ prefix: '/api/v1' })
         );
       }
 
+      classificationCounter.labels(classificationResult.predictedDiseaseSlug).inc();
+
       const db = createDbClient();
       let diseaseRow;
       try {
diff --git a/apps/api/src/routes/diagnoses.ts b/apps/api/src/routes/diagnoses.ts
index 4d8f1fd..b839f6b 100644
--- a/apps/api/src/routes/diagnoses.ts
+++ b/apps/api/src/routes/diagnoses.ts
@@ -9,6 +9,7 @@ import { getCurrentUser } from '../lib/auth';
 import { classifyImage } from '../lib/image-model';
 import { uploadImageToStorage } from '../lib/uploader-client';
 import { env } from '../config/env';
+import { diagnosisCounter } from '../lib/telemetry';
 
 interface ReviewRow {
   reviewId: string | null;
@@ -222,6 +223,9 @@ export const diagnosisRoutes = new Elysia({ prefix: '/api/v1' })
 
       const record = await loadDiagnosisRecord(inserted[0].id, user.id, false);
       if (!record) return serviceUnavailable('Database unavailable');
+
+      diagnosisCounter.labels(record.predictedDiseaseSlug ?? 'unknown').inc();
+
       return record;
     } catch (error) {
       const inserted = await db
@@ -240,6 +244,9 @@ export const diagnosisRoutes = new Elysia({ prefix: '/api/v1' })
 
       const record = await loadDiagnosisRecord(inserted[0].id, user.id, false);
       if (!record) return serviceUnavailable('Database unavailable');
+
+      diagnosisCounter.labels('failed').inc();
+
       return record;
     }
   })
diff --git a/apps/api/src/routes/metrics.ts b/apps/api/src/routes/metrics.ts
new file mode 100644
index 0000000..86c6ced
--- /dev/null
+++ b/apps/api/src/routes/metrics.ts
@@ -0,0 +1,10 @@
+import { Elysia } from 'elysia';
+import { getMetrics, getMetricsContentType } from '../lib/telemetry';
+
+export const metricsRoutes = new Elysia()
+  .get('/metrics', async () => {
+    const body = await getMetrics();
+    return new Response(body, {
+      headers: { 'Content-Type': getMetricsContentType() },
+    });
+  });
diff --git a/apps/api/src/types.ts b/apps/api/src/types.ts
new file mode 100644
index 0000000..be30f73
--- /dev/null
+++ b/apps/api/src/types.ts
@@ -0,0 +1,8 @@
+declare global {
+  interface Request {
+    metricsStart?: number;
+    metricsPath?: string;
+  }
+}
+
+export {};