diff --git a/docs/guide/vaults.md b/docs/guide/vaults.md
index 771b8f1e..5bf189e6 100644
--- a/docs/guide/vaults.md
+++ b/docs/guide/vaults.md
@@ -167,7 +167,7 @@ A flexible HTTP vault that speaks one of three wire protocols, selected with `ap
         password: "your-api-token"
     ```
 
-    Requests are `POST`ed as `{"method": ..., "params": ..., "token": ...}` using methods like `GetKey`, `InsertKey`, and `GetServices`. This mode cannot list all keys in bulk, so a `kv copy` from a json vault relies on the remote server's own duplicate handling.
+    Requests are `POST`ed as `{"method": ..., "params": ..., "token": ...}` using methods like `GetKey`, `InsertKey`, and `GetServices`. Bulk writes (`kv copy`, `kv add`) first try `InsertKeys` with `params: {"keys": {kid: key, ...}, "service": ..., "title": ...}` (up to 500 content keys per call) and expect `{"inserted": <count>}` back. A server that answers HTTP 404 to `InsertKeys` gets one `InsertKey` call per content key for the rest of the run instead. This mode cannot list all keys in bulk, so a `kv copy` from a json vault relies on the remote server's own duplicate handling.
 
 === "decrypt_labs mode"
 
diff --git a/unshackle/commands/kv.py b/unshackle/commands/kv.py
index 2491a354..fc8cc828 100644
--- a/unshackle/commands/kv.py
+++ b/unshackle/commands/kv.py
@@ -57,7 +57,7 @@ def process_service_keys(from_vault: Vault, service: str, log: logging.Logger) -
 
 def add_keys_with_progress(vault: Vault, service: str, kid_keys: dict[str, str], log: logging.Logger) -> int:
     """Add content keys to a vault in batches, with a progress bar of counts and time left."""
-    chunk = 1 if type(vault).__name__ == "HTTP" else 500
+    chunk = 1 if type(vault).__name__ == "HTTP" and getattr(vault, "api_mode", None) != "json" else 500
     kids = list(kid_keys)
     added = 0
     console.print()
diff --git a/unshackle/vaults/HTTP.py b/unshackle/vaults/HTTP.py
index 6d3235f3..3a79cdf6 100644
--- a/unshackle/vaults/HTTP.py
+++ b/unshackle/vaults/HTTP.py
@@ -57,6 +57,7 @@ class HTTP(Vault):
 
         self.username = username
         self.api_mode = api_mode.lower()
+        self.batch_insert = True
         self.current_title = None
         self.session = Session()
         self.session.headers.update({"User-Agent": f"unshackle v{__version__}"})
@@ -278,6 +279,18 @@ class HTTP(Vault):
         title = getattr(self, "current_title", None)
 
         if self.api_mode == "json":
+            if self.batch_insert:
+                try:
+                    response = self.request(
+                        "InsertKeys", {"keys": processed_kid_keys, "service": service.lower(), "title": title}
+                    )
+                    if response.get("status") != "not_found":
+                        return int(response.get("inserted", 0))
+                    # only a 404 proves the server has no InsertKeys method; other
+                    # failures may be transient, so keep batching for the next call
+                    self.batch_insert = False
+                except Exception:
+                    pass
             for kid, key in processed_kid_keys.items():
                 try:
                     response = self.request(