diff --git a/src/index.ts b/src/index.ts
index dd2933d..cca38f6 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -295,9 +295,14 @@ async function main() {
       // Check headers in order of preference
       const apiKey =
         extractBearerToken(req.headers.authorization) ||
-        extractHeaderValue(req.headers["X-Context7-API-Key"]) || // Standard with x- prefix
-        extractHeaderValue(req.headers["Context7-API-Key"]) || // Without x- prefix
-        extractHeaderValue(req.headers["X-API-Key"]); // Generic API key header
+        extractHeaderValue(req.headers["Context7-API-Key"]) ||
+        extractHeaderValue(req.headers["X-API-Key"]) ||
+        extractHeaderValue(req.headers["context7-api-key"]) ||
+        extractHeaderValue(req.headers["x-api-key"]) ||
+        extractHeaderValue(req.headers["Context7_API_Key"]) ||
+        extractHeaderValue(req.headers["X_API_Key"]) ||
+        extractHeaderValue(req.headers["context7_api_key"]) ||
+        extractHeaderValue(req.headers["x_api_key"]);
 
       try {
         // Extract client IP address using socket remote address (most reliable)
@@ -384,7 +389,7 @@ async function main() {
     startServer(initialPort);
   } else {
     // Stdio transport - this is already stateless by nature
-    const server = createServerInstance(cliOptions.apiKey);
+    const server = createServerInstance(undefined, cliOptions.apiKey);
     const transport = new StdioServerTransport();
     await server.connect(transport);
     console.error("Context7 Documentation MCP Server running on stdio");
diff --git a/src/lib/api.ts b/src/lib/api.ts
index 57a1f7c..8e27764 100644
--- a/src/lib/api.ts
+++ b/src/lib/api.ts
@@ -26,10 +26,17 @@ export async function searchLibraries(
     if (!response.ok) {
       const errorCode = response.status;
       if (errorCode === 429) {
-        console.error(`Rate limited due to too many requests. Please try again later.`);
+        console.error("Rate limited due to too many requests. Please try again later.");
         return {
           results: [],
-          error: `Rate limited due to too many requests. Please try again later.`,
+          error: "Rate limited due to too many requests. Please try again later.",
+        } as SearchResponse;
+      }
+      if (errorCode === 401) {
+        console.error("Unauthorized. Please check your API key.");
+        return {
+          results: [],
+          error: "Unauthorized. Please check your API key.",
         } as SearchResponse;
       }
       console.error(`Failed to search libraries. Please try again later. Error code: ${errorCode}`);
@@ -77,7 +84,18 @@ export async function fetchLibraryDocumentation(
     if (!response.ok) {
       const errorCode = response.status;
       if (errorCode === 429) {
-        const errorMessage = `Rate limited due to too many requests. Please try again later.`;
+        const errorMessage = "Rate limited due to too many requests. Please try again later.";
+        console.error(errorMessage);
+        return errorMessage;
+      }
+      if (errorCode === 404) {
+        const errorMessage =
+          "The library you are trying to access does not exist. Please try with a different library ID.";
+        console.error(errorMessage);
+        return errorMessage;
+      }
+      if (errorCode === 401) {
+        const errorMessage = "Unauthorized. Please check your API key.";
         console.error(errorMessage);
         return errorMessage;
       }