diff --git a/src/ApiUsage.tsx b/src/ApiUsage.tsx
index 820b6e7..f6495c9 100644
--- a/src/ApiUsage.tsx
+++ b/src/ApiUsage.tsx
@@ -145,6 +145,7 @@ export default function ApiUsage() {
   const [apiResponse, setApiResponse] = useState<any>(null);
   const [responseTime, setResponseTime] = useState<number | null>(null);
   const [callCost, setCallCost] = useState<number | null>(null);
+  const [statusFilter, setStatusFilter] = useState<'all' | 'success' | 'error'>('all');
   const [callHistory, setCallHistory] = useState<CallRecord[]>(MOCK_CALL_HISTORY);
   const [statusFilter, setStatusFilter] = useState<'all' | 'success' | 'error'>('all');
   const filteredCallHistory = statusFilter === 'all' ? callHistory : callHistory.filter(call => call.status === statusFilter);
@@ -368,19 +369,36 @@ export default function ApiUsage() {
           </div>
           
           <button
-            className="primary-button"
+            className={`primary-button ${isLoading ? 'button-loading' : ''}`}
             onClick={handleMakeTestCall}
             disabled={isLoading}
           >
+            {isLoading && <span className="button-spinner" aria-hidden="true" />}
             {isLoading ? 'Making Call...' : 'Make Test Call'}
           </button>
         </div>
         
         {(apiResponse || isLoading) && (
-          <div className="response-display">
+          <div 
+            className="response-display"
+            aria-live="polite"
+            aria-busy={isLoading}
+          >
             <h3>Response</h3>
             {isLoading ? (
-              <div className="loading-placeholder">Loading...</div>
+              <div className="response-content">
+                <div className="response-meta">
+                  <Skeleton width="120px" height="18px" borderRadius="4px" />
+                  <Skeleton width="100px" height="18px" borderRadius="4px" />
+                </div>
+                <div className="response-json-skeleton">
+                  <Skeleton width="60%" height="16px" borderRadius="4px" />
+                  <Skeleton width="80%" height="16px" borderRadius="4px" />
+                  <Skeleton width="45%" height="16px" borderRadius="4px" />
+                  <Skeleton width="70%" height="16px" borderRadius="4px" />
+                  <Skeleton width="30%" height="16px" borderRadius="4px" />
+                </div>
+              </div>
             ) : (
               <div className="response-content">
                 <div className="response-meta">
diff --git a/src/App.tsx b/src/App.tsx
index b3decd6..c37e669 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -5,6 +5,7 @@ import ApiUsage from './ApiUsage';
 import Dashboard from './components/Dashboard';
 import ServerError from './components/ServerError';
 import NotFound from './components/NotFound';
+import Dashboard from './components/Dashboard';
 
 type DepositStage = 'input' | 'approving' | 'pending' | 'confirmed' | 'failed';
 type DemoOutcome = 'confirmed' | 'failed';
diff --git a/src/components/FiltersSidebar.tsx b/src/components/FiltersSidebar.tsx
index 2c57e78..a4f98f0 100644
--- a/src/components/FiltersSidebar.tsx
+++ b/src/components/FiltersSidebar.tsx
@@ -57,26 +57,52 @@ export default function FiltersSidebar({
             <legend className="filter-legend">Price range</legend>
             <div className="filter-price" style={{ marginTop: 8, display: "flex", gap: 8 }}>
               <input
+                id="min-price-input"
                 type="number"
-                className="filter-input"
+                min="0"
+                className={`filter-input ${minPrice !== null && maxPrice !== null && minPrice > maxPrice ? 'filter-input--invalid' : ''}`}
                 placeholder="min"
                 value={minPrice ?? ""}
-                onChange={(e) =>
-                  setMinPrice(e.target.value === "" ? null : Number(e.target.value))
-                }
+                onChange={(e) => {
+                  const val = e.target.value === "" ? null : Math.max(0, Number(e.target.value));
+                  setMinPrice(val);
+                }}
+                aria-invalid={minPrice !== null && maxPrice !== null && minPrice > maxPrice}
+                aria-describedby={minPrice !== null && maxPrice !== null && minPrice > maxPrice ? "price-range-error" : undefined}
                 style={{ width: "100%" }}
               />
               <input
+                id="max-price-input"
                 type="number"
-                className="filter-input"
+                min="0"
+                className={`filter-input ${minPrice !== null && maxPrice !== null && minPrice > maxPrice ? 'filter-input--invalid' : ''}`}
                 placeholder="max"
                 value={maxPrice ?? ""}
-                onChange={(e) =>
-                  setMaxPrice(e.target.value === "" ? null : Number(e.target.value))
-                }
+                onChange={(e) => {
+                  const val = e.target.value === "" ? null : Math.max(0, Number(e.target.value));
+                  setMaxPrice(val);
+                }}
+                aria-invalid={minPrice !== null && maxPrice !== null && minPrice > maxPrice}
+                aria-describedby={minPrice !== null && maxPrice !== null && minPrice > maxPrice ? "price-range-error" : undefined}
                 style={{ width: "100%" }}
               />
             </div>
+            {minPrice !== null && maxPrice !== null && minPrice > maxPrice && (
+              <div 
+                id="price-range-error" 
+                style={{ 
+                  color: "var(--danger)", 
+                  fontSize: "0.8rem", 
+                  marginTop: 6, 
+                  display: "flex", 
+                  alignItems: "center", 
+                  gap: 4 
+                }}
+                role="alert"
+              >
+                <span>⚠️</span> Min price cannot exceed max price.
+              </div>
+            )}
           </fieldset>
       </div>
 
diff --git a/src/index.css b/src/index.css
index 94e48bb..49bdbe9 100644
--- a/src/index.css
+++ b/src/index.css
@@ -31,6 +31,27 @@
     rgba(20, 27, 50, 0.98),
     rgba(12, 18, 34, 0.98)
   );
+
+  /* HTTP Method Badge Tokens - Dark Theme (High Contrast / Accessible) */
+  --method-get-bg: rgba(59, 130, 246, 0.16);
+  --method-get-color: #60a5fa;
+  --method-get-border: rgba(59, 130, 246, 0.35);
+
+  --method-post-bg: rgba(16, 185, 129, 0.16);
+  --method-post-color: #34d399;
+  --method-post-border: rgba(16, 185, 129, 0.35);
+
+  --method-put-bg: rgba(245, 158, 11, 0.16);
+  --method-put-color: #fbbf24;
+  --method-put-border: rgba(245, 158, 11, 0.35);
+
+  --method-delete-bg: rgba(239, 68, 68, 0.16);
+  --method-delete-color: #f87171;
+  --method-delete-border: rgba(239, 68, 68, 0.35);
+
+  --method-patch-bg: rgba(139, 92, 246, 0.16);
+  --method-patch-color: #a78bfa;
+  --method-patch-border: rgba(139, 92, 246, 0.35);
 }
 
 [data-theme="light"] {
@@ -55,6 +76,27 @@
     rgba(255, 255, 255, 0.98),
     rgba(248, 250, 255, 0.98)
   );
+
+  /* HTTP Method Badge Tokens - Light Theme (High Contrast / Accessible) */
+  --method-get-bg: rgba(37, 99, 235, 0.1);
+  --method-get-color: #1e40af;
+  --method-get-border: rgba(37, 99, 235, 0.25);
+
+  --method-post-bg: rgba(5, 150, 105, 0.1);
+  --method-post-color: #065f46;
+  --method-post-border: rgba(5, 150, 105, 0.25);
+
+  --method-put-bg: rgba(217, 119, 6, 0.1);
+  --method-put-color: #92400e;
+  --method-put-border: rgba(217, 119, 6, 0.25);
+
+  --method-delete-bg: rgba(220, 38, 38, 0.1);
+  --method-delete-color: #991b1b;
+  --method-delete-border: rgba(220, 38, 38, 0.25);
+
+  --method-patch-bg: rgba(109, 40, 217, 0.1);
+  --method-patch-color: #5b21b6;
+  --method-patch-border: rgba(109, 40, 217, 0.25);
 }
 
 * {
@@ -2668,3 +2710,102 @@ code,
   color: var(--text);
   cursor: pointer;
 }
+
+/* Button Spinner & Loading States */
+@keyframes spin {
+  to {
+    transform: rotate(360deg);
+  }
+}
+
+.button-spinner {
+  display: inline-block;
+  width: 16px;
+  height: 16px;
+  border: 2px solid rgba(255, 255, 255, 0.3);
+  border-top-color: #ffffff;
+  border-radius: 50%;
+  animation: spin 0.6s linear infinite;
+  margin-right: 8px;
+  flex-shrink: 0;
+}
+
+.primary-button.button-loading {
+  cursor: not-allowed;
+}
+
+/* Response JSON Skeleton Container */
+.response-json-skeleton {
+  background: var(--surface);
+  padding: 16px;
+  border-radius: 8px;
+  display: flex;
+  flex-direction: column;
+  gap: 12px;
+}
+
+/* Accessible HTTP Method Badges */
+.method-badge {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  padding: 4px 8px;
+  border-radius: 6px;
+  font-size: 0.72rem;
+  font-weight: 800;
+  text-transform: uppercase;
+  letter-spacing: 0.05em;
+  border: 1px solid transparent;
+}
+
+.method-badge--get {
+  background: var(--method-get-bg);
+  color: var(--method-get-color);
+  border-color: var(--method-get-border);
+}
+
+.method-badge--post {
+  background: var(--method-post-bg);
+  color: var(--method-post-color);
+  border-color: var(--method-post-border);
+}
+
+.method-badge--put {
+  background: var(--method-put-bg);
+  color: var(--method-put-color);
+  border-color: var(--method-put-border);
+}
+
+.method-badge--patch {
+  background: var(--method-patch-bg);
+  color: var(--method-patch-color);
+  border-color: var(--method-patch-border);
+}
+
+.method-badge--delete {
+  background: var(--method-delete-bg);
+  color: var(--method-delete-color);
+  border-color: var(--method-delete-border);
+}
+
+/* Price Filter Input Validation Styles */
+.filter-input {
+  padding: 8px 12px;
+  background: var(--page-bg);
+  border: 1px solid var(--line);
+  border-radius: 6px;
+  color: var(--text);
+  transition: border-color 0.2s, box-shadow 0.2s;
+}
+
+.filter-input--invalid {
+  border-color: var(--danger) !important;
+}
+
+.filter-input--invalid:focus-visible {
+  outline: 2px solid var(--danger) !important;
+  box-shadow: 0 0 0 3px rgba(255, 125, 141, 0.4) !important;
+}
+
+
+
diff --git a/src/pages/ApiDetailPage.tsx b/src/pages/ApiDetailPage.tsx
index 415fcb4..e76e34c 100644
--- a/src/pages/ApiDetailPage.tsx
+++ b/src/pages/ApiDetailPage.tsx
@@ -549,15 +549,7 @@ print(data)`;
                           <div className="endpoint-card-header">
                             <div className="endpoint-title-row">
                               <span
-                                style={{
-                                  padding: "4px 8px",
-                                  background:
-                                    ep.method === "GET" ? "#3b82f6" : "#10b981",
-                                  color: "white",
-                                  borderRadius: 4,
-                                  fontSize: 11,
-                                  fontWeight: 800,
-                                }}
+                                className={`method-badge method-badge--${(ep.method || 'get').toLowerCase()}`}
                               >
                                 {ep.method}
                               </span>
diff --git a/src/pages/MarketplacePage.tsx b/src/pages/MarketplacePage.tsx
index fdca792..75122cc 100644
--- a/src/pages/MarketplacePage.tsx
+++ b/src/pages/MarketplacePage.tsx
@@ -63,10 +63,13 @@ export default function MarketplacePage(): JSX.Element {
       items = items.filter((a) => selectedCategories.has(a.category ?? ""));
     }
 
-    if (minPrice !== null)
-      items = items.filter((a) => a.pricePerRequest >= minPrice);
-    if (maxPrice !== null)
-      items = items.filter((a) => a.pricePerRequest <= maxPrice);
+    const hasInvertedPrice = minPrice !== null && maxPrice !== null && minPrice > maxPrice;
+    if (!hasInvertedPrice) {
+      if (minPrice !== null)
+        items = items.filter((a) => a.pricePerRequest >= minPrice);
+      if (maxPrice !== null)
+        items = items.filter((a) => a.pricePerRequest <= maxPrice);
+    }
 
     // popularity-based ordering
     if (popularity === "mostUsed") {