diff --git a/apps/ml-service/src/routes.rs b/apps/ml-service/src/routes.rs
index edd9033..3d0cc09 100644
--- a/apps/ml-service/src/routes.rs
+++ b/apps/ml-service/src/routes.rs
@@ -130,18 +130,33 @@ pub async fn predict(
     };
 
     // Preprocess the image
+    let preprocess_start = std::time::Instant::now();
     let input = preprocess_image(&bytes, state.model.input_size())?;
 
-    // Run prediction
-    let prediction = state.model.predict(input)?;
+    // Record image size metric
+    telemetry::image_size_bytes().observe(bytes.len() as f64);
 
-    // Record business and request telemetry
+    // Run prediction with timing
+    let inference_start = std::time::Instant::now();
+    let prediction = state.model.predict(input)?;
+    telemetry::inference_duration_seconds().observe(inference_start.elapsed().as_secs_f64());
+
+    // Record business telemetry
     telemetry::predictions_total().inc();
+    telemetry::predictions_by_class()
+        .with_label_values(&[&prediction.label])
+        .inc();
+    telemetry::predictions_confidence().observe(prediction.confidence as f64);
     _guard.finish();
 
     Ok(Json(prediction_response(prediction)))
 }
 
+/// Helper to record errors from route handlers
+pub fn record_error(kind: &str) {
+    telemetry::errors_total().with_label_values(&[kind]).inc();
+}
+
 pub fn router(state: AppState) -> Router {
     Router::new()
         .route("/health", get(health))
diff --git a/apps/ml-service/src/telemetry.rs b/apps/ml-service/src/telemetry.rs
index 6a08d15..44c36fc 100644
--- a/apps/ml-service/src/telemetry.rs
+++ b/apps/ml-service/src/telemetry.rs
@@ -1,4 +1,4 @@
-use prometheus::{Counter, Gauge, Histogram, HistogramOpts, Registry, TextEncoder};
+use prometheus::{Counter, CounterVec, Gauge, Histogram, HistogramOpts, HistogramVec, Opts, Registry, TextEncoder};
 use std::sync::OnceLock;
 use std::time::Instant;
 
@@ -78,6 +78,76 @@ define_metric!(
     .expect("create gauge")
 );
 
+/// Per-class prediction counter
+define_metric!(
+    predictions_by_class,
+    CounterVec,
+    CounterVec::new(
+        Opts::new(
+            "zeavis_ml_predictions_by_class_total",
+            "Total predictions by predicted class label",
+        ),
+        &["label"],
+    )
+    .expect("create counter_vec")
+);
+
+/// Per-class ground-truth counter (for monitoring label distribution)
+define_metric!(
+    predictions_confidence,
+    Histogram,
+    Histogram::with_opts(
+        HistogramOpts::new(
+            "zeavis_ml_prediction_confidence",
+            "Confidence values of predictions",
+        )
+        .buckets(vec![0.0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.85, 0.9, 0.95, 0.99, 1.0]),
+    )
+    .expect("create histogram")
+);
+
+/// Latency of ONNX inference (model.predict call)
+define_metric!(
+    inference_duration_seconds,
+    Histogram,
+    Histogram::with_opts(
+        HistogramOpts::new(
+            "zeavis_ml_inference_duration_seconds",
+            "ONNX model inference duration in seconds",
+        )
+        .buckets(vec![0.01, 0.025, 0.05, 0.1, 0.2, 0.3, 0.5, 0.75, 1.0, 2.0]),
+    )
+    .expect("create histogram")
+);
+
+/// Image size processed by the ML service
+define_metric!(
+    image_size_bytes,
+    Histogram,
+    Histogram::with_opts(
+        HistogramOpts::new(
+            "zeavis_ml_image_size_bytes",
+            "Size of images sent for prediction in bytes",
+        )
+        .buckets(vec![1024.0, 10240.0, 51200.0, 102400.0, 204800.0, 512000.0, 1048576.0, 2097152.0]),
+    )
+    .expect("create histogram")
+);
+
+/// Error counter by error kind (e.g. bad_request, model_error, internal)
+define_metric!(
+    errors_total,
+    CounterVec,
+    CounterVec::new(
+        Opts::new(
+            "zeavis_ml_errors_total",
+            "Total errors by kind",
+        ),
+        &["kind"],
+    )
+    .expect("create counter_vec")
+);
+
 // ── Request Guard (Drop-based cleanup for active gauge) ─
 
 pub struct RequestMetricsGuard {
diff --git a/apps/web/src/lib/telemetry.ts b/apps/web/src/lib/telemetry.ts
index 46f3255..cdaf84d 100644
--- a/apps/web/src/lib/telemetry.ts
+++ b/apps/web/src/lib/telemetry.ts
@@ -2,8 +2,10 @@
  * Client‑side telemetry for the ZeaVis Edu web app.
  *
  * In development, metrics are collected in‑memory and exposed at /metrics
- * via a Vite plugin.  In production they are sent as HTTP beacons to the
- * Telemetry pipeline (see METRICS.md).
+ * via a Vite plugin.  In production they are served through the same plugin
+ * (or proxied by nginx in production mode).
+ *
+ * Metric name prefix: zeavis_web_
  */
 
 // ── Web Vitals ──────────────────────────────────────────
@@ -18,35 +20,99 @@ const vitalsBuffer: MetricEntry[] = [];
 
 export function reportWebVitals(metric: MetricEntry): void {
   vitalsBuffer.push(metric);
-  // Keep last 20 entries in memory for the /metrics endpoint
-  if (vitalsBuffer.length > 20) vitalsBuffer.shift();
-  console.debug(`[telemetry] ${metric.name}: ${metric.value} (${metric.rating ?? 'n/a'})`);
+  if (vitalsBuffer.length > 30) vitalsBuffer.splice(0, vitalsBuffer.length - 30);
 }
 
 // ── Page‑view counter ───────────────────────────────────
 
 let pageViewCount = 0;
+const routeViews: Record<string, number> = {};
 
 export function trackPageView(path: string): void {
   pageViewCount++;
-  console.debug(`[telemetry] pageview: ${path} (total: ${pageViewCount})`);
+  routeViews[path] = (routeViews[path] || 0) + 1;
 }
 
-// ── Metrics serialisation (consumed by vite‑plugin) ────
+// ── API call timing ─────────────────────────────────────
+// Track how long API calls take from the browser side
+
+const apiLatencies: number[] = [];
+const MAX_API_SAMPLES = 100;
+
+export function recordApiCall(method: string, path: string, durationMs: number, status: number): void {
+  apiLatencies.push(durationMs);
+  if (apiLatencies.length > MAX_API_SAMPLES) apiLatencies.shift();
+  console.debug(`[telemetry] api ${method} ${path} → ${status} (${durationMs.toFixed(0)}ms)`);
+}
+
+// ── Error tracking (client-side JS errors) ──────────────
+
+let errorCount = 0;
+
+export function trackError(source: string): void {
+  errorCount++;
+  console.debug(`[telemetry] error from ${source} (total: ${errorCount})`);
+}
+
+// ── Diagnosis actions ───────────────────────────────────
+
+let scanCount = 0;
+let diagnosisSuccess = 0;
+let diagnosisFailure = 0;
+
+export function trackScan(): void {
+  scanCount++;
+}
+
+export function trackDiagnosisResult(success: boolean): void {
+  if (success) diagnosisSuccess++;
+  else diagnosisFailure++;
+}
+
+// ── Metrics serialisation (consumed by vite-plugin) ────
 
 export function collectMetrics(): string {
   const lines: string[] = [];
 
-  // ── Default process‑like metrics ──────────────────────
   lines.push('# HELP zeavis_web_page_views_total Total page views');
   lines.push('# TYPE zeavis_web_page_views_total counter');
   lines.push(`zeavis_web_page_views_total ${pageViewCount}`);
 
-  lines.push('# HELP zeavis_web_vital_bucket Web Vitals observed this session');
-  lines.push('# TYPE zeavis_web_vital_bucket gauge');
-  for (const v of vitalsBuffer) {
-    lines.push(`zeavis_web_vital_bucket{name="${v.name}",rating="${v.rating ?? 'unknown'}"} ${v.value}`);
+  lines.push('# HELP zeavis_web_route_views_total Page views per route');
+  lines.push('# TYPE zeavis_web_route_views_total counter');
+  for (const [route, count] of Object.entries(routeViews)) {
+    lines.push(`zeavis_web_route_views_total{route="${route}"} ${count}`);
   }
 
+  lines.push('# HELP zeavis_web_vital Web Vitals observed this session');
+  lines.push('# TYPE zeavis_web_vital gauge');
+  for (const v of vitalsBuffer) {
+    lines.push(`zeavis_web_vital{name="${v.name}",rating="${v.rating ?? 'unknown'}"} ${v.value}`);
+  }
+
+  if (apiLatencies.length > 0) {
+    const avg = apiLatencies.reduce((a, b) => a + b, 0) / apiLatencies.length;
+    lines.push('# HELP zeavis_web_api_call_duration_ms Average API call duration from browser');
+    lines.push('# TYPE zeavis_web_api_call_duration_ms gauge');
+    lines.push(`zeavis_web_api_call_duration_ms ${avg.toFixed(2)}`);
+  }
+
+  lines.push('# HELP zeavis_web_client_errors_total Client-side JS errors');
+  lines.push('# TYPE zeavis_web_client_errors_total counter');
+  lines.push(`zeavis_web_client_errors_total ${errorCount}`);
+
+  lines.push('# HELP zeavis_web_scans_total Scan button clicks');
+  lines.push('# TYPE zeavis_web_scans_total counter');
+  lines.push(`zeavis_web_scans_total ${scanCount}`);
+
+  lines.push('# HELP zeavis_web_diagnoses_total Diagnosis results from browser');
+  lines.push('# TYPE zeavis_web_diagnoses_total counter');
+  lines.push(`zeavis_web_diagnoses_total{result="success"} ${diagnosisSuccess}`);
+  lines.push(`zeavis_web_diagnoses_total{result="failure"} ${diagnosisFailure}`);
+
+  lines.push('# HELP zeavis_web_active_users User activity (1 = active this session)');
+  lines.push('# TYPE zeavis_web_active_users gauge');
+  lines.push(`zeavis_web_active_users 1`);
+
   return lines.join('\n') + '\n';
 }