diff --git a/README.md b/README.md
index 654c2374..5710370f 100644
--- a/README.md
+++ b/README.md
@@ -270,6 +270,24 @@ and `seo_injected` events under `github-actions`. Generated files stay in the
 temporary runner; this workflow does not commit changes or publish the site.
 Pull request tests and preset-update jobs continue to run without analytics.
 
+### Website usage analytics
+
+`analytics.js` loads the PostHog browser SDK on `presets.polymaker.com` using the
+public write-only project token. Local and preview hosts do not send PostHog
+events. This is separate from the Node build SDK and GitHub Actions secrets.
+
+PostHog records pageviews (`$pageview`), page leaves, automatic interactions
+(`$autocapture`), and `filter_changed` with the selected filter and value.
+The existing successful-download handlers send `download_single`,
+`download_selected`, `download_bundle`, and `download_bundle_batch` to both
+Google Analytics and PostHog, including material/printer/slicer metadata where
+available. A download event means the browser was handed the generated file;
+it cannot confirm the user saved or imported it. Session recording is disabled.
+
+View these events in PostHog **Activity**, or use **Web analytics** for visits
+and **Product analytics** for filter and download usage. Ad blockers or a
+visitor's analytics opt-out can prevent events from arriving.
+
 ## 🔗 Links
 
 - **Download Page**: [https://presets.polymaker.com](https://presets.polymaker.com) 
diff --git a/analytics.js b/analytics.js
new file mode 100644
index 00000000..80f8cc91
--- /dev/null
+++ b/analytics.js
@@ -0,0 +1,47 @@
+// Browser analytics. This is the public, write-only PostHog project token.
+// The Node build client is configured separately through GitHub Actions secrets.
+(function () {
+  if (window.location.hostname !== 'presets.polymaker.com') return;
+  if (window.posthog && (window.posthog.__loaded || window.posthog.__SV)) return;
+
+  // PostHog's asynchronous snippet queues early interactions while the SDK loads.
+  // https://posthog.com/docs/libraries/js
+  var posthog = window.posthog = [];
+  posthog._i = [];
+  posthog.__SV = 1;
+  posthog.people = [];
+  posthog.init = function (token, config) {
+    var script = document.createElement('script');
+    script.type = 'text/javascript';
+    script.crossOrigin = 'anonymous';
+    script.async = true;
+    script.src = config.api_host.replace('.i.posthog.com', '-assets.i.posthog.com') + '/static/array.js';
+    var firstScript = document.getElementsByTagName('script')[0];
+    firstScript.parentNode.insertBefore(script, firstScript);
+
+    function queueMethod(name) {
+      posthog[name] = function () {
+        posthog.push([name].concat(Array.prototype.slice.call(arguments)));
+      };
+    }
+    var methods = ['capture', 'register', 'identify', 'reset', 'set_config', 'opt_in_capturing', 'opt_out_capturing'];
+    for (var i = 0; i < methods.length; i++) queueMethod(methods[i]);
+    posthog._i.push([token, config, 'posthog']);
+  };
+
+  window.posthog.init('phc_CdvtTDKLvkXysqQN43CbH674J2p9r9LoEZBGEHbrfsYi', {
+    api_host: 'https://us.i.posthog.com',
+    ui_host: 'https://us.posthog.com',
+    defaults: '2026-05-30',
+    capture_pageview: true,
+    capture_pageleave: true,
+    autocapture: true,
+    person_profiles: 'identified_only',
+    cross_subdomain_cookie: false,
+    disable_session_recording: true,
+    disable_surveys: true,
+    loaded: function (posthog) {
+      posthog.register({ site: 'polymaker-presets' });
+    }
+  });
+}());
diff --git a/app.js b/app.js
index 5ff57cb3..c8a7c4db 100644
--- a/app.js
+++ b/app.js
@@ -23,14 +23,23 @@ function getGaValue(value) {
   return value;
 }
 
-function trackGaEvent(eventName, params) {
+function trackUsageEvent(eventName, params) {
   if (typeof window === 'undefined') return;
-  if (typeof window.gtag !== 'function') return;
+  // Each provider is independent: blocked analytics must never break downloads.
   try {
-    window.gtag('event', eventName, params || {});
+    if (typeof window.gtag === 'function') {
+      window.gtag('event', eventName, params || {});
+    }
   } catch (e) {
     console.warn('GA event failed:', eventName, e);
   }
+  try {
+    if (window.posthog && typeof window.posthog.capture === 'function') {
+      window.posthog.capture(eventName, params || {});
+    }
+  } catch (e) {
+    console.warn('PostHog event failed:', eventName, e);
+  }
 }
 
 function applyTheme(theme) {
@@ -537,7 +546,7 @@ function init() {
       document.body.removeChild(a);
       if (originalPresets && originalPresets.length) {
         var firstPreset = originalPresets[0];
-        trackGaEvent('download_bundle', {
+        trackUsageEvent('download_bundle', {
           file_type: 'bbsflmt',
           slicer: getGaValue(firstPreset.slicer || 'BambuStudio'),
           material: getGaValue(firstPreset.material),
@@ -776,6 +785,15 @@ function init() {
           }
 
           render();
+          trackUsageEvent('filter_changed', {
+            filter: name,
+            value: value || 'all',
+            series: filterState.series || 'all',
+            brand: filterState.brand || 'all',
+            model: filterState.model || 'all',
+            slicer: filterState.slicer || 'all',
+            strict: filterState.strict
+          });
         });
       }
 
@@ -1046,7 +1064,7 @@ function init() {
             a.click();
             document.body.removeChild(a);
             var filters = getEffectiveFilters();
-            trackGaEvent('download_selected', {
+            trackUsageEvent('download_selected', {
               file_type: 'zip',
               selected_count: presetIds.length,
               slicer: getGaValue(filters.effectiveSlicer || filterState.slicer),
@@ -1269,7 +1287,7 @@ function init() {
           document.body.appendChild(a);
           a.click();
           document.body.removeChild(a);
-          trackGaEvent('download_bundle_batch', {
+          trackUsageEvent('download_bundle_batch', {
             file_type: 'zip',
             material_count: materials.length,
             slicer: 'BambuStudio'
@@ -1516,6 +1534,7 @@ function init() {
         strictCheckbox.addEventListener('change', function () {
           filterState.strict = strictCheckbox.checked;
           render();
+          trackUsageEvent('filter_changed', { filter: 'strict', value: filterState.strict });
         });
       }
 
@@ -1823,8 +1842,8 @@ function init() {
               a.click();
               document.body.removeChild(a);
               var rowContext = getRowGaContext(directJsonLink.closest('tr'));
-              trackGaEvent('download_single', {
-                file_type: 'json',
+              trackUsageEvent('download_single', {
+                file_type: /\.ini$/i.test(djFilename) ? 'ini' : 'json',
                 slicer: rowContext.slicer,
                 material: rowContext.material,
                 brand: rowContext.brand,
@@ -1879,7 +1898,7 @@ function init() {
                   a.click();
                   document.body.removeChild(a);
                   var rowContext = getRowGaContext(bambuJsonLink.closest('tr'), 'BambuStudio');
-                  trackGaEvent('download_single', {
+                  trackUsageEvent('download_single', {
                     file_type: 'json',
                     slicer: rowContext.slicer,
                     material: getGaValue(bjMaterial || rowContext.material),
diff --git a/index.html b/index.html
index 49bc5bba..f19806fa 100644
--- a/index.html
+++ b/index.html
@@ -17,6 +17,7 @@
   <link rel="stylesheet" href="style.css">
   <link href="https://fonts.googleapis.com/css2?family=Noto+Sans+SC:wght@300;400;500;700&display=swap" rel="stylesheet">
   <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.5.1/css/all.min.css" crossorigin="anonymous">
+  <script src="analytics.js"></script>
   <!-- Google tag (gtag.js) -->
   <script async src="https://www.googletagmanager.com/gtag/js?id=G-KXL1MCXGJZ"></script>
   <script>
diff --git a/scripts/website-analytics.test.mjs b/scripts/website-analytics.test.mjs
new file mode 100644
index 00000000..51f2d229
--- /dev/null
+++ b/scripts/website-analytics.test.mjs
@@ -0,0 +1,94 @@
+import { it } from 'node:test';
+import assert from 'node:assert/strict';
+import { readFileSync } from 'node:fs';
+import vm from 'node:vm';
+
+const analytics = readFileSync(new URL('../analytics.js', import.meta.url), 'utf8');
+const app = readFileSync(new URL('../app.js', import.meta.url), 'utf8');
+const helper = app.slice(app.indexOf('function trackUsageEvent('), app.indexOf('function applyTheme('));
+
+function browser(hostname = 'presets.polymaker.com') {
+  const scripts = [];
+  const context = vm.createContext({
+    window: { location: { hostname } },
+    document: {
+      createElement: () => ({}),
+      getElementsByTagName: () => [{ parentNode: { insertBefore: (script) => scripts.push(script) } }],
+    },
+    console: { warn() {} },
+  });
+  vm.runInContext(analytics, context);
+  vm.runInContext(helper, context);
+  return { context, scripts };
+}
+
+it('loads the browser SDK asynchronously and queues usage before it arrives', () => {
+  const { context, scripts } = browser();
+  assert.equal(scripts.length, 1);
+  assert.equal(scripts[0].src, 'https://us-assets.i.posthog.com/static/array.js');
+  assert.equal(scripts[0].async, true);
+  const [, config] = context.window.posthog._i[0];
+  assert.equal(config.capture_pageview, true);
+  assert.equal(config.autocapture, true);
+  assert.equal(config.disable_session_recording, true);
+  vm.runInContext("trackUsageEvent('download_single', {material: 'Panchroma PLA'});", context);
+  assert.equal(context.window.posthog[0][0], 'capture');
+  assert.equal(context.window.posthog[0][1], 'download_single');
+  assert.equal(context.window.posthog[0][2].material, 'Panchroma PLA');
+  vm.runInContext(analytics, context);
+  assert.equal(scripts.length, 1, 'reloading bootstrap must not initialize twice');
+});
+
+it('does not load production analytics on local or preview hosts', () => {
+  for (const host of ['localhost', '127.0.0.1', 'preview.example.com']) {
+    const { context, scripts } = browser(host);
+    assert.equal(scripts.length, 0);
+    assert.doesNotThrow(() => vm.runInContext("trackUsageEvent('download_single');", context));
+  }
+});
+
+it('sends to both providers independently, even when one is unavailable or throws', () => {
+  const { context } = browser();
+  const ga = [];
+  const ph = [];
+  context.window.gtag = (...args) => ga.push(args);
+  context.window.posthog = { capture: (...args) => ph.push(args) };
+  vm.runInContext("trackUsageEvent('download_selected', {selected_count: 2});", context);
+  assert.equal(ga.length, 1);
+  assert.equal(ph.length, 1);
+  assert.equal(ph[0][1].selected_count, 2);
+  context.window.gtag = () => { throw new Error('blocked GA'); };
+  vm.runInContext("trackUsageEvent('download_bundle');", context);
+  assert.equal(ph.length, 2);
+  context.window.gtag = (...args) => ga.push(args);
+  context.window.posthog.capture = () => { throw new Error('blocked PostHog'); };
+  assert.doesNotThrow(() => vm.runInContext("trackUsageEvent('download_bundle_batch');", context));
+  assert.equal(ga.length, 2);
+});
+
+it('captures a real dropdown selection after rendering its new filter state', () => {
+  const { context } = browser();
+  let select;
+  let rendered = false;
+  const option = { getAttribute: () => 'OrcaSlicer', textContent: 'OrcaSlicer', classList: { add() {} } };
+  const menu = { addEventListener: (_, fn) => { select = fn; }, querySelector: () => null };
+  const dropdown = {
+    querySelector: (selector) => selector === '.dropdown-menu' ? menu : { addEventListener() {} },
+    classList: { remove() {} },
+  };
+  Object.assign(context, {
+    filterState: { slicer: '', series: '', brand: '', model: '', strict: true },
+    selectedPresets: {}, escapeHtml: (s) => s, t: (s) => s,
+    updateVisibility() {}, updateBrandDropdownState() {}, updateSelectedCount() {},
+    render() { rendered = true; },
+  });
+  context.document.querySelector = () => dropdown;
+  vm.runInContext(app.slice(app.indexOf('function setupDropdown('), app.indexOf('function closeAllDropdowns(')), context);
+  vm.runInContext("setupDropdown('slicer', ['OrcaSlicer'], true);", context);
+  select({ target: { closest: () => option } });
+  assert.equal(rendered, true);
+  const event = context.window.posthog[0];
+  assert.equal(event[1], 'filter_changed');
+  assert.equal(event[2].filter, 'slicer');
+  assert.equal(event[2].slicer, 'OrcaSlicer');
+});