diff --git a/web_app/static/index.html b/web_app/static/index.html
index 0d56371..6ad94e8 100644
--- a/web_app/static/index.html
+++ b/web_app/static/index.html
@@ -116,7 +116,10 @@ <h2 id="contentHeading">Lyrics</h2>
                                 </div>
                             </div>
 
-                            <button id="generateBtn" class="primary-btn">Generate Poster</button>
+                            <button id="generateBtn" class="primary-btn">
+                                <span class="btn-text">Generate Poster</span>
+                                <span class="btn-spinner"></span>
+                            </button>
                         </div>
                     </div>
 
diff --git a/web_app/static/script.js b/web_app/static/script.js
index 441a4ed..be4fcb0 100644
--- a/web_app/static/script.js
+++ b/web_app/static/script.js
@@ -20,7 +20,6 @@ const startLineInput = document.getElementById('startLine');
 const endLineInput = document.getElementById('endLine');
 const themeInput = document.getElementById('themeInput');
 const fontInput = document.getElementById('fontInput');
-const loadingOverlay = document.getElementById('loadingOverlay');
 
 let currentMetadata = null;
 let searchDebounceTimer = null;
@@ -613,7 +612,8 @@ function handleLyricLineClick(lineNumber) {
 async function generatePoster() {
     if (!currentMetadata) return;
 
-    loadingOverlay.style.display = 'flex';
+    generateBtn.classList.add('loading');
+    generateBtn.disabled = true;
 
     const indexingToggle = document.getElementById('indexingToggle');
     const accentToggle = document.getElementById('accentToggle');
@@ -635,7 +635,8 @@ async function generatePoster() {
         const end = endVal;
 
         if (isNaN(start) || isNaN(end) || start >= end) {
-            loadingOverlay.style.display = 'none';
+            generateBtn.classList.remove('loading');
+            generateBtn.disabled = false;
             showToast("Please enter a valid range (Start must be less than End).", "error");
             return;
         }
@@ -669,13 +670,20 @@ async function generatePoster() {
             posterContainer.innerHTML = '';
             posterContainer.appendChild(img);
             showDownloadButton(imageUrl, data.filename);
-            loadingOverlay.style.display = 'none';
+            generateBtn.classList.remove('loading');
+            generateBtn.disabled = false;
+        };
+        img.onerror = () => {
+            showToast("Error loading generated image.", "error");
+            generateBtn.classList.remove('loading');
+            generateBtn.disabled = false;
         };
 
     } catch (error) {
         console.error("Generation failed", error);
         showToast(`Error: ${error.message}`, "error");
-        loadingOverlay.style.display = 'none';
+        generateBtn.classList.remove('loading');
+        generateBtn.disabled = false;
     }
 }
 
diff --git a/web_app/static/style.css b/web_app/static/style.css
index 468eb76..906cfb0 100644
--- a/web_app/static/style.css
+++ b/web_app/static/style.css
@@ -908,4 +908,53 @@ input:focus {
 
 .result-action svg {
     pointer-events: none;
-}
\ No newline at end of file
+}
+
+/* --- Button Loading State --- */
+.primary-btn {
+    position: relative; /* Needed for spinner positioning */
+}
+
+.btn-spinner {
+    display: none;
+    position: absolute;
+    top: 50%;
+    left: 50%;
+    transform: translate(-50%, -50%);
+    width: 20px;
+    height: 20px;
+    border: 2px solid rgba(0, 0, 0, 0.2);
+    border-top-color: #1a1a1f; /* Spinner color matching button text */
+    border-radius: 50%;
+    animation: btn-spin 0.8s linear infinite;
+}
+
+.btn-text {
+    transition: opacity 0.2s ease, visibility 0.2s ease;
+}
+
+/* Loading state */
+.primary-btn.loading .btn-text {
+    visibility: hidden;
+    opacity: 0;
+}
+
+.primary-btn.loading .btn-spinner {
+    display: block;
+}
+
+.primary-btn.loading {
+    cursor: wait;
+    background: var(--accent-hover);
+    pointer-events: none; /* Disables clicks while loading */
+}
+
+
+@keyframes btn-spin {
+    from {
+        transform: translate(-50%, -50%) rotate(0deg);
+    }
+    to {
+        transform: translate(-50%, -50%) rotate(360deg);
+    }
+}