diff --git a/src/agent/agent_loop.rs b/src/agent/agent_loop.rs
index 3f6ead5..70aae0a 100644
--- a/src/agent/agent_loop.rs
+++ b/src/agent/agent_loop.rs
@@ -72,24 +72,28 @@ fn encode_image_to_base64(path: &str) -> Result<(String, String), std::io::Error
 /// Truncate tool result if it exceeds MAX_TOOL_RESULT_CHARS.
 /// Preserves the end of the output as it often contains the conclusion/useful result.
 fn truncate_tool_result(output: &str) -> String {
-    if output.len() <= MAX_TOOL_RESULT_CHARS {
+    let char_count = output.chars().count();
+    if char_count <= MAX_TOOL_RESULT_CHARS {
         return output.to_string();
     }
 
-    let truncated_start_len = output.len().saturating_sub(TRUNCATION_SUFFIX_LEN);
+    let truncated_start_len = char_count.saturating_sub(TRUNCATION_SUFFIX_LEN);
     if truncated_start_len > MAX_TOOL_RESULT_CHARS {
         // Even after removing suffix, still too long - take from beginning
+        let head_len = MAX_TOOL_RESULT_CHARS - 100;
+        let head: String = output.chars().take(head_len).collect();
         format!(
             "{}...\n\n[Output truncated - {} characters removed]",
-            &output[..MAX_TOOL_RESULT_CHARS - 100],
-            output.len() - MAX_TOOL_RESULT_CHARS + 100
+            head,
+            char_count - MAX_TOOL_RESULT_CHARS + 100
         )
     } else {
         // Keep most of the end which usually contains the useful result
+        let tail: String = output.chars().skip(truncated_start_len).collect();
         format!(
             "...\n\n[Output truncated - {} characters removed]\n\n{}",
             truncated_start_len,
-            &output[truncated_start_len..]
+            tail
         )
     }
 }
@@ -1036,6 +1040,16 @@ mod tests {
         assert_eq!(provider_message.tool_calls.as_ref().unwrap()[0].name, "calculator");
     }
 
+    #[test]
+    fn test_truncate_tool_result_handles_utf8_char_boundaries() {
+        let input = "范".repeat(MAX_TOOL_RESULT_CHARS + 500);
+
+        let output = truncate_tool_result(&input);
+
+        assert!(output.contains("Output truncated"));
+        assert!(output.is_char_boundary(output.len()));
+    }
+
     #[test]
     fn test_did_successfully_write_memory_only_accepts_successful_put_or_update() {
         let tool_call = ToolCall {