diff --git a/open-sse/translator/formats.js b/open-sse/translator/formats.js
index 6828868..ebfed28 100644
--- a/open-sse/translator/formats.js
+++ b/open-sse/translator/formats.js
@@ -21,6 +21,9 @@ export function detectFormatByEndpoint(pathname, body) {
   // /v1/responses is always openai-responses
   if (pathname.includes("/v1/responses")) return FORMATS.OPENAI_RESPONSES;
 
+  // /v1/messages is always Claude
+  if (pathname.includes("/v1/messages")) return FORMATS.CLAUDE;
+
   // /v1/chat/completions + input[] → treat as openai (Cursor CLI sends Responses body via chat endpoint)
   if (pathname.includes("/v1/chat/completions") && Array.isArray(body?.input)) {
     return FORMATS.OPENAI;
diff --git a/open-sse/translator/helpers/openaiHelper.js b/open-sse/translator/helpers/openaiHelper.js
index 90879b9..1872393 100644
--- a/open-sse/translator/helpers/openaiHelper.js
+++ b/open-sse/translator/helpers/openaiHelper.js
@@ -87,7 +87,7 @@ export function filterToOpenAIFormat(body) {
           type: "function",
           function: {
             name: tool.name,
-            description: tool.description || "",
+            description: String(tool.description || ""),
             parameters: tool.input_schema || { type: "object", properties: {} }
           }
         };
@@ -99,7 +99,7 @@ export function filterToOpenAIFormat(body) {
           type: "function",
           function: {
             name: fn.name,
-            description: fn.description || "",
+            description: String(fn.description || ""),
             parameters: fn.parameters || { type: "object", properties: {} }
           }
         }));
diff --git a/open-sse/translator/request/claude-to-openai.js b/open-sse/translator/request/claude-to-openai.js
index d954593..0bb284e 100644
--- a/open-sse/translator/request/claude-to-openai.js
+++ b/open-sse/translator/request/claude-to-openai.js
@@ -59,7 +59,7 @@ export function claudeToOpenAIRequest(model, body, stream) {
       type: "function",
       function: {
         name: tool.name,
-        description: tool.description,
+        description: String(tool.description || ""),
         parameters: tool.input_schema || { type: "object", properties: {} }
       }
     }));
diff --git a/open-sse/translator/request/openai-responses.js b/open-sse/translator/request/openai-responses.js
index 3468ac8..4501a33 100644
--- a/open-sse/translator/request/openai-responses.js
+++ b/open-sse/translator/request/openai-responses.js
@@ -138,7 +138,7 @@ export function openaiResponsesToOpenAIRequest(model, body, stream, credentials)
           type: "function",
           function: {
             name,
-            description: tool.description,
+            description: String(tool.description || ""),
             parameters: tool.parameters,
             strict: tool.strict
           }
@@ -259,7 +259,7 @@ export function openaiToOpenAIResponsesRequest(model, body, stream, credentials)
         return {
           type: "function",
           name: tool.function.name,
-          description: tool.function.description,
+          description: String(tool.function.description || ""),
           parameters: tool.function.parameters,
           strict: tool.function.strict
         };