diff --git a/lib/upload-api.ts b/lib/upload-api.ts
index 72efbce..c3a7b91 100644
--- a/lib/upload-api.ts
+++ b/lib/upload-api.ts
@@ -27,6 +27,8 @@ type UploadJsonBody =
   | { stagingId: string }
   | { stagingId: string; action: DriveAction }
 
+const RESPONSE_PREVIEW_MAX_LENGTH = 160
+
 function getApiError(data: unknown, fallback: string) {
   return isRecord(data) && typeof data.error === 'string' ? data.error : fallback
 }
@@ -48,6 +50,50 @@ function getUploadJsonHeaders(secret: string) {
   }
 }
 
+function getResponsePreview(body: string) {
+  return body
+    .replace(/<[^>]*>/g, ' ')
+    .replace(/\s+/g, ' ')
+    .trim()
+    .slice(0, RESPONSE_PREVIEW_MAX_LENGTH)
+}
+
+function getUnexpectedJsonResponseError(res: Response, body: string) {
+  const contentType = res.headers.get('content-type') || 'type inconnu'
+  const preview = getResponsePreview(body)
+  const detail = preview ? ` Detail : ${preview}` : ''
+
+  if (res.status === 413) {
+    return `Upload trop volumineux ou bloque par le proxy (${res.status}). Verifiez la limite de taille Coolify/Nginx.${detail}`
+  }
+
+  if (res.status === 502 || res.status === 503 || res.status === 504) {
+    return `API upload indisponible (${res.status}). Le serveur a probablement redemarre ou plante pendant le traitement.${detail}`
+  }
+
+  return `Reponse serveur inattendue (${res.status}, ${contentType}).${detail}`
+}
+
+async function readUploadJson(res: Response): Promise<unknown> {
+  const body = await res.text()
+
+  if (body.trim() === '') {
+    return {}
+  }
+
+  const contentType = res.headers.get('content-type') || ''
+
+  if (!contentType.toLowerCase().includes('json')) {
+    throw new Error(getUnexpectedJsonResponseError(res, body))
+  }
+
+  try {
+    return JSON.parse(body)
+  } catch {
+    throw new Error(getUnexpectedJsonResponseError(res, body))
+  }
+}
+
 async function postUploadJson(
   endpoint: string,
   secret: string,
@@ -61,7 +107,7 @@ async function postUploadJson(
     signal,
   })
 
-  const data: unknown = await res.json()
+  const data = await readUploadJson(res)
   return { res, data }
 }
 
@@ -165,7 +211,7 @@ export async function stageUpload(
     signal,
   })
 
-  const data: unknown = await res.json()
+  const data = await readUploadJson(res)
 
   if (!res.ok || !isSuccessfulUploadData(data)) {
     throw new Error(getApiError(data, `Erreur serveur (${res.status})`))