diff --git a/server/src/wled_controller/static/js/core/ui.js b/server/src/wled_controller/static/js/core/ui.js
index 9ff5bf2..88b6222 100644
--- a/server/src/wled_controller/static/js/core/ui.js
+++ b/server/src/wled_controller/static/js/core/ui.js
@@ -163,10 +163,28 @@ export function showOverlaySpinner(text, duration = 0) {
         existing.remove();
     }
 
+    // AbortController for cancelling in-flight fetch
+    window._overlayAbortController = new AbortController();
+
     const overlay = document.createElement('div');
     overlay.id = 'overlay-spinner';
     overlay.className = 'overlay-spinner';
 
+    // Close button
+    const closeBtn = document.createElement('button');
+    closeBtn.className = 'overlay-spinner-close';
+    closeBtn.innerHTML = '×';
+    closeBtn.title = 'Cancel';
+    closeBtn.onclick = () => hideOverlaySpinner();
+    overlay.appendChild(closeBtn);
+
+    // ESC key handler
+    function onEsc(e) {
+        if (e.key === 'Escape') hideOverlaySpinner();
+    }
+    window._overlayEscHandler = onEsc;
+    document.addEventListener('keydown', onEsc);
+
     const progressContainer = document.createElement('div');
     progressContainer.className = 'progress-container';
 
@@ -235,6 +253,14 @@ export function hideOverlaySpinner() {
         clearInterval(window.overlaySpinnerTimer);
         window.overlaySpinnerTimer = null;
     }
+    if (window._overlayEscHandler) {
+        document.removeEventListener('keydown', window._overlayEscHandler);
+        window._overlayEscHandler = null;
+    }
+    if (window._overlayAbortController) {
+        window._overlayAbortController.abort();
+        window._overlayAbortController = null;
+    }
     const overlay = document.getElementById('overlay-spinner');
     if (overlay) overlay.remove();
 }
diff --git a/server/src/wled_controller/static/js/features/streams.js b/server/src/wled_controller/static/js/features/streams.js
index 5ef57da..4bc4269 100644
--- a/server/src/wled_controller/static/js/features/streams.js
+++ b/server/src/wled_controller/static/js/features/streams.js
@@ -298,6 +298,7 @@ export async function runTemplateTest() {
 
     const template = window.currentTestingTemplate;
     showOverlaySpinner(t('templates.test.running'), captureDuration);
+    const signal = window._overlayAbortController?.signal;
 
     try {
         const response = await fetchWithAuth('/capture-templates/test', {
@@ -307,7 +308,8 @@ export async function runTemplateTest() {
                 engine_config: template.engine_config,
                 display_index: parseInt(displayIndex),
                 capture_duration: captureDuration
-            })
+            }),
+            signal
         });
 
         if (!response.ok) {
@@ -319,6 +321,7 @@ export async function runTemplateTest() {
         localStorage.setItem('lastTestDisplayIndex', displayIndex);
         displayTestResults(result);
     } catch (error) {
+        if (error.name === 'AbortError') return;
         console.error('Error running test:', error);
         hideOverlaySpinner();
         showToast(t('templates.test.error.failed'), 'error');
@@ -980,11 +983,13 @@ export async function runStreamTest() {
     if (!_currentTestStreamId) return;
     const captureDuration = parseFloat(document.getElementById('test-stream-duration').value);
     showOverlaySpinner(t('streams.test.running'), captureDuration);
+    const signal = window._overlayAbortController?.signal;
 
     try {
         const response = await fetchWithAuth(`/picture-sources/${_currentTestStreamId}/test`, {
             method: 'POST',
-            body: JSON.stringify({ capture_duration: captureDuration })
+            body: JSON.stringify({ capture_duration: captureDuration }),
+            signal
         });
         if (!response.ok) {
             const error = await response.json();
@@ -995,6 +1000,7 @@ export async function runStreamTest() {
         const fullImageSrc = result.full_capture.full_image || result.full_capture.image;
         openLightbox(fullImageSrc, buildTestStatsHtml(result));
     } catch (error) {
+        if (error.name === 'AbortError') return;
         console.error('Error running stream test:', error);
         hideOverlaySpinner();
         showToast(t('streams.test.error.failed') + ': ' + error.message, 'error');
@@ -1057,11 +1063,13 @@ export async function runPPTemplateTest() {
 
     const captureDuration = parseFloat(document.getElementById('test-pp-duration').value);
     showOverlaySpinner(t('postprocessing.test.running'), captureDuration);
+    const signal = window._overlayAbortController?.signal;
 
     try {
         const response = await fetchWithAuth(`/postprocessing-templates/${_currentTestPPTemplateId}/test`, {
             method: 'POST',
-            body: JSON.stringify({ source_stream_id: sourceStreamId, capture_duration: captureDuration })
+            body: JSON.stringify({ source_stream_id: sourceStreamId, capture_duration: captureDuration }),
+            signal
         });
         if (!response.ok) {
             const error = await response.json();
@@ -1072,6 +1080,7 @@ export async function runPPTemplateTest() {
         const fullImageSrc = result.full_capture.full_image || result.full_capture.image;
         openLightbox(fullImageSrc, buildTestStatsHtml(result));
     } catch (error) {
+        if (error.name === 'AbortError') return;
         console.error('Error running PP template test:', error);
         hideOverlaySpinner();
         showToast(t('postprocessing.test.error.failed') + ': ' + error.message, 'error');
diff --git a/server/src/wled_controller/static/locales/en.json b/server/src/wled_controller/static/locales/en.json
index defefb9..65b886b 100644
--- a/server/src/wled_controller/static/locales/en.json
+++ b/server/src/wled_controller/static/locales/en.json
@@ -237,6 +237,7 @@
   "confirm.title": "Confirm Action",
   "confirm.yes": "Yes",
   "confirm.no": "No",
+  "common.loading": "Loading...",
   "common.delete": "Delete",
   "common.edit": "Edit",
   "streams.title": "\uD83D\uDCFA Sources",
diff --git a/server/src/wled_controller/static/locales/ru.json b/server/src/wled_controller/static/locales/ru.json
index 5f53c64..e568873 100644
--- a/server/src/wled_controller/static/locales/ru.json
+++ b/server/src/wled_controller/static/locales/ru.json
@@ -237,6 +237,7 @@
   "confirm.title": "Подтверждение Действия",
   "confirm.yes": "Да",
   "confirm.no": "Нет",
+  "common.loading": "Загрузка...",
   "common.delete": "Удалить",
   "common.edit": "Редактировать",
   "streams.title": "\uD83D\uDCFA Источники",
diff --git a/server/src/wled_controller/static/style.css b/server/src/wled_controller/static/style.css
index 15e41a7..4c41f44 100644
--- a/server/src/wled_controller/static/style.css
+++ b/server/src/wled_controller/static/style.css
@@ -1006,6 +1006,24 @@ input:-webkit-autofill:focus {
     font-weight: 500;
 }
 
+.overlay-spinner-close {
+    position: absolute;
+    top: 16px;
+    right: 16px;
+    background: none;
+    border: none;
+    color: rgba(255, 255, 255, 0.6);
+    font-size: 32px;
+    cursor: pointer;
+    line-height: 1;
+    padding: 4px 8px;
+    transition: color 0.15s;
+}
+
+.overlay-spinner-close:hover {
+    color: white;
+}
+
 @keyframes spin {
     to { transform: rotate(360deg); }
 }