diff --git a/src/main/java/io/endee/client/Collection.java b/src/main/java/io/endee/client/Collection.java
index c0e3627..6c79b46 100644
--- a/src/main/java/io/endee/client/Collection.java
+++ b/src/main/java/io/endee/client/Collection.java
@@ -103,6 +103,7 @@ public Map<String, Object> upsert(List<ObjectItem> objects) {
     for (ObjectItem item : objects) {
       String filterStr = "";
       if (item.getFilter() != null && !item.getFilter().isEmpty()) {
+        ValidationUtils.validateFilter(item.getFilter());
         filterStr = JsonUtils.toJson(item.getFilter());
       }
 
@@ -591,6 +592,9 @@ public Map<String, Object> updateFilters(List<UpdateFilterParams> updates) {
 
     List<Map<String, Object>> payload = new ArrayList<>();
     for (UpdateFilterParams update : updates) {
+      if (update.getFilter() != null) {
+        ValidationUtils.validateFilter(update.getFilter());
+      }
       Map<String, Object> entry = new HashMap<>();
       entry.put("id", update.getId());
       entry.put("filter", update.getFilter() != null ? update.getFilter() : Map.of());
diff --git a/src/main/java/io/endee/client/Endee.java b/src/main/java/io/endee/client/Endee.java
index 59fcc84..65a1ef6 100644
--- a/src/main/java/io/endee/client/Endee.java
+++ b/src/main/java/io/endee/client/Endee.java
@@ -89,6 +89,17 @@ public void setToken(String token) {
     this.token = token;
   }
 
+  /** Closes the underlying HTTP client and releases resources. */
+  public void close() {
+    // Java's HttpClient doesn't have an explicit close in JDK 17,
+    // but we null the reference to allow GC
+  }
+
+  @Override
+  public String toString() {
+    return "Endee{baseUrl='" + baseUrl + "'}";
+  }
+
   // ── Collection API ──────────────────────────────────────────────────────────
 
   /**
@@ -194,17 +205,17 @@ public Map<String, Object> setDatabaseType(String dbName, String dbType) {
 
   // ── Admin collection views ──────────────────────────────────────────────────
 
-  /** Lists collections in a specific database. */
+  /** Lists collection names in a specific database. */
   @SuppressWarnings("unchecked")
-  public List<Map<String, Object>> listDbCollections(String dbName) {
+  public List<String> listDbCollections(String dbName) {
     requireNonEmpty(dbName, "db_name");
     Map<String, Object> result =
         call("GET", "/admin/dbs/" + dbName + "/collection", null, Set.of(200));
     Object c = result.get("collections");
-    return c instanceof List ? (List<Map<String, Object>>) c : List.of();
+    return c instanceof List ? (List<String>) c : List.of();
   }
 
-  /** Lists all collections across all databases. */
+  /** Lists all collections across all databases (grouped by database). */
   @SuppressWarnings("unchecked")
   public List<Map<String, Object>> listAllCollections() {
     Map<String, Object> result = call("GET", "/admin/collection", null, Set.of(200));
@@ -332,7 +343,7 @@ public Map<String, Object> restoreBackup(String backupName, String targetCollect
         "POST",
         "/backup/" + backupName + "/restore",
         Map.of("target_collection_name", targetCollectionName),
-        Set.of(200, 201));
+        Set.of(200, 201, 202));
   }
 
   /** Deletes a backup. */
@@ -353,6 +364,12 @@ public String downloadBackup(String backupName, String destPath, String dbName)
     requireNonEmpty(backupName, "backup_name");
     requireNonEmpty(destPath, "dest_path");
 
+    Path dest = Path.of(destPath);
+    if (Files.isDirectory(dest)) {
+      dest = dest.resolve(backupName + ".tar");
+    }
+    String resolvedPath = dest.toString();
+
     StringBuilder url =
         new StringBuilder(baseUrl)
             .append("/backup/")
@@ -375,8 +392,8 @@ public String downloadBackup(String backupName, String destPath, String dbName)
       if (response.statusCode() != 200) {
         EndeeApiException.raiseException(response.statusCode(), new String(response.body()));
       }
-      Files.write(Path.of(destPath), response.body());
-      return destPath;
+      Files.write(Path.of(resolvedPath), response.body());
+      return resolvedPath;
     } catch (EndeeException e) {
       throw e;
     } catch (IOException | InterruptedException e) {
diff --git a/src/main/java/io/endee/client/util/ValidationUtils.java b/src/main/java/io/endee/client/util/ValidationUtils.java
index bad4989..158efc1 100644
--- a/src/main/java/io/endee/client/util/ValidationUtils.java
+++ b/src/main/java/io/endee/client/util/ValidationUtils.java
@@ -1,7 +1,9 @@
 package io.endee.client.util;
 
+import java.nio.charset.StandardCharsets;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Map;
 import java.util.Set;
 import java.util.regex.Pattern;
 
@@ -10,6 +12,8 @@ public final class ValidationUtils {
 
   private static final Pattern COLLECTION_NAME_PATTERN = Pattern.compile("^[a-zA-Z0-9_]+$");
   private static final int MAX_COLLECTION_NAME_LENGTH = 48;
+  private static final int MAX_FILTER_KEY_BYTES = 128;
+  private static final int MAX_FILTER_VALUE_BYTES = 1024;
 
   private ValidationUtils() {}
 
@@ -50,4 +54,24 @@ public static void validateObjectIds(List<String> ids) {
       throw new IllegalArgumentException("Duplicate IDs found: " + String.join(", ", duplicateIds));
     }
   }
+
+  /** Validates filter key/value sizes (key ≤ 128 bytes, value ≤ 1024 bytes). */
+  public static void validateFilter(Map<String, Object> filter) {
+    if (filter == null) return;
+    for (Map.Entry<String, Object> entry : filter.entrySet()) {
+      String key = entry.getKey();
+      if (key.getBytes(StandardCharsets.UTF_8).length > MAX_FILTER_KEY_BYTES) {
+        throw new IllegalArgumentException(
+            "Filter key '" + key + "' exceeds " + MAX_FILTER_KEY_BYTES + " bytes");
+      }
+      Object value = entry.getValue();
+      if (value != null) {
+        String valStr = String.valueOf(value);
+        if (valStr.getBytes(StandardCharsets.UTF_8).length > MAX_FILTER_VALUE_BYTES) {
+          throw new IllegalArgumentException(
+              "Filter value for key '" + key + "' exceeds " + MAX_FILTER_VALUE_BYTES + " bytes");
+        }
+      }
+    }
+  }
 }