diff --git a/pages/api/nip95-upload.ts b/pages/api/nip95-upload.ts
index d6694fa..b5f14a5 100644
--- a/pages/api/nip95-upload.ts
+++ b/pages/api/nip95-upload.ts
@@ -243,6 +243,29 @@ export default async function handler(req: NextApiRequest, res: NextApiResponse)
       })
     }
 
+    // Check if response is HTML (error page) instead of JSON
+    const trimmedBody = response.body.trim()
+    const isHtml = trimmedBody.startsWith('<!DOCTYPE') || trimmedBody.startsWith('<html') || trimmedBody.startsWith('<!')
+    
+    if (isHtml) {
+      // Try to extract error message from HTML if possible
+      const titleMatch = response.body.match(/<title[^>]*>([^<]+)<\/title>/i)
+      const h1Match = response.body.match(/<h1[^>]*>([^<]+)<\/h1>/i)
+      const errorText = titleMatch?.[1] || h1Match?.[1] || 'HTML error page returned'
+      
+      console.error('NIP-95 proxy HTML response error:', {
+        targetEndpoint,
+        finalUrl: currentUrl.toString(),
+        status: response.statusCode,
+        errorText,
+        bodyPreview: response.body.substring(0, 200),
+      })
+      
+      return res.status(500).json({
+        error: `Endpoint returned an HTML error page instead of JSON. The endpoint may be unavailable or the URL may be incorrect. Error: ${errorText}`,
+      })
+    }
+
     let result: unknown
     try {
       result = JSON.parse(response.body)
@@ -254,7 +277,7 @@ export default async function handler(req: NextApiRequest, res: NextApiResponse)
         bodyPreview: response.body.substring(0, 100),
       })
       return res.status(500).json({
-        error: `Invalid upload response: ${errorMessage}`,
+        error: `Invalid upload response: ${errorMessage}. The endpoint may not be a valid NIP-95 upload endpoint.`,
       })
     }