diff --git a/src/mcp/mod.rs b/src/mcp/mod.rs
index 81b7da3..7e91be9 100644
--- a/src/mcp/mod.rs
+++ b/src/mcp/mod.rs
@@ -3,7 +3,9 @@ use crate::core::models::SearchOptions;
 use crate::core::patent_search::{PatentSearch, PatentSearcher};
 use rmcp::{
     handler::server::{tool::ToolRouter, wrapper::Parameters},
-    model::{Implementation, ProtocolVersion, ServerCapabilities, ServerInfo, ToolsCapability},
+    model::{
+        ErrorCode, Implementation, ProtocolVersion, ServerCapabilities, ServerInfo, ToolsCapability,
+    },
     schemars::{self, JsonSchema},
     service::{NotificationContext, RequestContext},
     tool, tool_handler, tool_router, ErrorData, RoleServer, ServerHandler, ServiceExt,
@@ -69,7 +71,7 @@ impl PatentHandler {
     pub async fn search_patents(
         &self,
         Parameters(request): Parameters<SearchPatentsRequest>,
-    ) -> String {
+    ) -> Result<String, ErrorData> {
         let options = SearchOptions {
             query: request.query,
             assignee: request.assignee,
@@ -81,10 +83,13 @@ impl PatentHandler {
             language: request.language,
         };
 
-        match self.searcher.search(&options).await {
-            Ok(results) => serde_json::to_string_pretty(&results).unwrap_or_default(),
-            Err(e) => format!("Search failed: {}", e),
-        }
+        self.searcher
+            .search(&options)
+            .await
+            .map(|results| serde_json::to_string_pretty(&results).unwrap_or_default())
+            .map_err(|e| {
+                ErrorData::new(ErrorCode::INTERNAL_ERROR, format!("Search failed: {}", e), None)
+            })
     }
 
     /// Fetch details of a specific patent by ID
@@ -92,13 +97,18 @@ impl PatentHandler {
     pub async fn fetch_patent(
         &self,
         Parameters(request): Parameters<FetchPatentRequest>,
-    ) -> String {
+    ) -> Result<String, ErrorData> {
         if request.raw {
-            match self.searcher.get_raw_html(&request.patent_id, request.language.as_deref()).await
-            {
-                Ok(html) => html,
-                Err(e) => format!("Failed to fetch raw HTML: {}", e),
-            }
+            self.searcher
+                .get_raw_html(&request.patent_id, request.language.as_deref())
+                .await
+                .map_err(|e| {
+                    ErrorData::new(
+                        ErrorCode::INTERNAL_ERROR,
+                        format!("Failed to fetch raw HTML: {}", e),
+                        None,
+                    )
+                })
         } else {
             let options = SearchOptions {
                 query: None,
@@ -112,10 +122,20 @@ impl PatentHandler {
             };
             match self.searcher.search(&options).await {
                 Ok(mut results) => results.patents.pop().map_or_else(
-                    || format!("No patent found with ID: {}", request.patent_id),
-                    |patent| serde_json::to_string_pretty(&patent).unwrap_or_default(),
+                    || {
+                        Err(ErrorData::new(
+                            ErrorCode::INVALID_PARAMS,
+                            format!("No patent found with ID: {}", request.patent_id),
+                            None,
+                        ))
+                    },
+                    |patent| Ok(serde_json::to_string_pretty(&patent).unwrap_or_default()),
                 ),
-                Err(e) => format!("Fetch failed: {}", e),
+                Err(e) => Err(ErrorData::new(
+                    ErrorCode::INTERNAL_ERROR,
+                    format!("Fetch failed: {}", e),
+                    None,
+                )),
             }
         }
     }
@@ -240,8 +260,10 @@ mod tests {
             language: None,
         };
         let result = handler.search_patents(Parameters(request)).await;
-        assert!(result.contains("SEARCH1"));
-        assert!(result.contains("Search Result"));
+        assert!(result.is_ok());
+        let result_str = result.unwrap();
+        assert!(result_str.contains("SEARCH1"));
+        assert!(result_str.contains("Search Result"));
     }
 
     #[tokio::test]
@@ -252,24 +274,30 @@ mod tests {
         let request =
             FetchPatentRequest { patent_id: "US123".to_string(), raw: false, language: None };
         let result = handler.fetch_patent(Parameters(request)).await;
-        assert!(result.contains("US123"));
+        assert!(result.is_ok());
+        assert!(result.unwrap().contains("US123"));
 
         // Raw HTML case
         let request =
             FetchPatentRequest { patent_id: "US123".to_string(), raw: true, language: None };
         let result = handler.fetch_patent(Parameters(request)).await;
-        assert_eq!(result, "<html>US123</html>");
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap(), "<html>US123</html>");
 
         // Not found case
         let request =
             FetchPatentRequest { patent_id: "NONE".to_string(), raw: false, language: None };
         let result = handler.fetch_patent(Parameters(request)).await;
-        assert!(result.contains("No patent found"));
+        assert!(result.is_err());
+        let err = result.unwrap_err();
+        assert!(err.message.contains("No patent found"));
 
         // Error case
         let request =
             FetchPatentRequest { patent_id: "FAIL".to_string(), raw: false, language: None };
         let result = handler.fetch_patent(Parameters(request)).await;
-        assert!(result.contains("Fetch failed"));
+        assert!(result.is_err());
+        let err = result.unwrap_err();
+        assert!(err.message.contains("Fetch failed"));
     }
 }