diff --git a/.jules/bolt.md b/.jules/bolt.md
new file mode 100644
index 0000000..2bcd17d
--- /dev/null
+++ b/.jules/bolt.md
@@ -0,0 +1,3 @@
+## 2024-06-30 - Hex Format Optimization
+**Learning:** Using String.format() in a loop to convert byte arrays to hex strings allocates many temporary objects (String, Object[] for varargs) and performs poorly. The application's DefaultDocumentConversionService previously used this pattern for hashing uploads, impacting memory and CPU heavily.
+**Action:** Always prefer java.util.HexFormat.of().formatHex(bytes) introduced in Java 17 for byte-to-hex conversion to improve performance, minimize object allocation, and make the code cleaner.
diff --git a/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java b/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java
index 9c59593..92e76a5 100644
--- a/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java
+++ b/src/main/java/com/clearfolio/viewer/service/DefaultDocumentConversionService.java
@@ -7,6 +7,7 @@
 import java.io.InputStream;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
+import java.util.HexFormat;
 
 import org.springframework.stereotype.Service;
 import org.springframework.web.multipart.MultipartFile;
@@ -121,12 +122,7 @@ private String contentHash(MultipartFile file) {
             }
 
             byte[] raw = digest.digest();
-            StringBuilder hex = new StringBuilder(raw.length * 2);
-            for (byte b : raw) {
-                hex.append(String.format("%02x", b));
-            }
-
-            return hex.toString();
+            return HexFormat.of().formatHex(raw);
         } catch (NoSuchAlgorithmException ex) {
             throw new IllegalStateException("SHA-256 digest unavailable", ex);
         } catch (IOException ex) {