From 308d19f6173481dba8d0f99062b125d1ff904642 Mon Sep 17 00:00:00 2001
From: Anubhav Dhawan <anubhavdhawan@google.com>
Date: Thu, 2 Jul 2026 06:03:12 +0530
Subject: [PATCH 01/14] feat(core): add custom protocols array support for
 ToolboxClient

---
 .../toolbox-core/src/toolbox_core/client.py   | 23 +++++++++++++++++--
 .../mcp_transport/transport_base.py           |  2 ++
 .../mcp_transport/v20250618/mcp.py            |  2 +-
 .../mcp_transport/v20251125/mcp.py            |  2 +-
 .../mcp_transport/v20260618/mcp.py            |  4 ++--
 5 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/packages/toolbox-core/src/toolbox_core/client.py b/packages/toolbox-core/src/toolbox_core/client.py
index b2224eedc..e05715bc1 100644
--- a/packages/toolbox-core/src/toolbox_core/client.py
+++ b/packages/toolbox-core/src/toolbox_core/client.py
@@ -53,12 +53,14 @@ def __init__(
         client_name: Optional[str],
         client_version: Optional[str],
         telemetry_enabled: bool,
+        supported_protocols: Optional[list[str]] = None,
     ):
         self._url = url
         self._session = session
         self._client_name = client_name
         self._client_version = client_version
         self._telemetry_enabled = telemetry_enabled
+        self._supported_protocols = supported_protocols
         self._active_transport = self._create_transport(protocol)
 
     def _create_transport(self, protocol: Protocol) -> ITransport:
@@ -71,6 +73,7 @@ def _create_transport(self, protocol: Protocol) -> ITransport:
                     self._client_name,
                     self._client_version,
                     telemetry_enabled=self._telemetry_enabled,
+                    supported_protocols=self._supported_protocols,
                 )
             case Protocol.MCP_v20251125:
                 return McpHttpTransportV20251125(
@@ -80,6 +83,7 @@ def _create_transport(self, protocol: Protocol) -> ITransport:
                     self._client_name,
                     self._client_version,
                     telemetry_enabled=self._telemetry_enabled,
+                    supported_protocols=self._supported_protocols,
                 )
             case Protocol.MCP_v20250618:
                 return McpHttpTransportV20250618(
@@ -89,6 +93,7 @@ def _create_transport(self, protocol: Protocol) -> ITransport:
                     self._client_name,
                     self._client_version,
                     telemetry_enabled=self._telemetry_enabled,
+                    supported_protocols=self._supported_protocols,
                 )
             case Protocol.MCP_v20250326:
                 return McpHttpTransportV20250326(
@@ -98,6 +103,7 @@ def _create_transport(self, protocol: Protocol) -> ITransport:
                     self._client_name,
                     self._client_version,
                     telemetry_enabled=self._telemetry_enabled,
+                    supported_protocols=self._supported_protocols,
                 )
             case Protocol.MCP_v20241105:
                 return McpHttpTransportV20241105(
@@ -107,6 +113,7 @@ def _create_transport(self, protocol: Protocol) -> ITransport:
                     self._client_name,
                     self._client_version,
                     telemetry_enabled=self._telemetry_enabled,
+                    supported_protocols=self._supported_protocols,
                 )
             case _:
                 raise ValueError(f"Unsupported MCP protocol version: {protocol}")
@@ -166,7 +173,7 @@ def __init__(
         client_headers: Optional[
             Mapping[str, Union[Callable[[], str], Callable[[], Awaitable[str]], str]]
         ] = None,
-        protocol: Protocol = Protocol.MCP,
+        protocol: Union[Protocol, list[Protocol], list[str]] = Protocol.MCP,
         client_name: Optional[str] = None,
         client_version: Optional[str] = None,
         telemetry_enabled: bool = False,
@@ -188,13 +195,25 @@ def __init__(
             telemetry_enabled: Whether to enable OpenTelemetry tracing and metrics. (Default: False)
         """
 
+        if isinstance(protocol, list):
+            if not protocol:
+                raise ValueError("protocol list cannot be empty")
+            supported_protocols = [
+                p.value if isinstance(p, Protocol) else str(p) for p in protocol
+            ]
+            initial_protocol = Protocol(supported_protocols[0])
+        else:
+            supported_protocols = None
+            initial_protocol = protocol
+
         self.__transport = _McpTransportProxy(
             url,
             session,
-            protocol,
+            initial_protocol,
             client_name,
             client_version,
             telemetry_enabled,
+            supported_protocols,
         )
 
         self.__client_headers = client_headers if client_headers is not None else {}
diff --git a/packages/toolbox-core/src/toolbox_core/mcp_transport/transport_base.py b/packages/toolbox-core/src/toolbox_core/mcp_transport/transport_base.py
index 735ae9066..1a70953eb 100644
--- a/packages/toolbox-core/src/toolbox_core/mcp_transport/transport_base.py
+++ b/packages/toolbox-core/src/toolbox_core/mcp_transport/transport_base.py
@@ -42,6 +42,7 @@ def __init__(
         client_name: Optional[str] = None,
         client_version: Optional[str] = None,
         telemetry_enabled: bool = False,
+        supported_protocols: Optional[list[str]] = None,
     ):
         self._mcp_base_url = f"{base_url}/mcp/"
         self._protocol_version = protocol.value
@@ -50,6 +51,7 @@ def __init__(
         self._client_name = client_name
         self._client_version = client_version
         self._telemetry_enabled = telemetry.resolve_telemetry_enabled(telemetry_enabled)
+        self._supported_protocols = supported_protocols or Protocol.get_supported_mcp_versions()
 
         self._tracer: Optional[telemetry.Tracer] = None
         self._operation_duration_histogram: Optional[telemetry.Histogram] = None
diff --git a/packages/toolbox-core/src/toolbox_core/mcp_transport/v20250618/mcp.py b/packages/toolbox-core/src/toolbox_core/mcp_transport/v20250618/mcp.py
index 2ea3ee636..35f759346 100644
--- a/packages/toolbox-core/src/toolbox_core/mcp_transport/v20250618/mcp.py
+++ b/packages/toolbox-core/src/toolbox_core/mcp_transport/v20250618/mcp.py
@@ -75,7 +75,7 @@ async def _send_request(
                 err_val = json_resp["error"]
                 if isinstance(err_val, dict) and err_val.get("code") == -32004:
                     server_supported = err_val.get("data", {}).get("supported", [])
-                    client_supported = Protocol.get_supported_mcp_versions()
+                    client_supported = self._supported_protocols
                     mutually_supported = [
                         v for v in client_supported if v in server_supported
                     ]
diff --git a/packages/toolbox-core/src/toolbox_core/mcp_transport/v20251125/mcp.py b/packages/toolbox-core/src/toolbox_core/mcp_transport/v20251125/mcp.py
index 4a0e8d876..bf365dece 100644
--- a/packages/toolbox-core/src/toolbox_core/mcp_transport/v20251125/mcp.py
+++ b/packages/toolbox-core/src/toolbox_core/mcp_transport/v20251125/mcp.py
@@ -75,7 +75,7 @@ async def _send_request(
                 err_val = json_resp["error"]
                 if isinstance(err_val, dict) and err_val.get("code") == -32004:
                     server_supported = err_val.get("data", {}).get("supported", [])
-                    client_supported = Protocol.get_supported_mcp_versions()
+                    client_supported = self._supported_protocols
                     mutually_supported = [
                         v for v in client_supported if v in server_supported
                     ]
diff --git a/packages/toolbox-core/src/toolbox_core/mcp_transport/v20260618/mcp.py b/packages/toolbox-core/src/toolbox_core/mcp_transport/v20260618/mcp.py
index 866249733..f7511e2e5 100644
--- a/packages/toolbox-core/src/toolbox_core/mcp_transport/v20260618/mcp.py
+++ b/packages/toolbox-core/src/toolbox_core/mcp_transport/v20260618/mcp.py
@@ -88,7 +88,7 @@ async def _send_request(
                                 "supported", []
                             )
 
-                            client_supported = Protocol.get_supported_mcp_versions()
+                            client_supported = self._supported_protocols
                             mutually_supported = [
                                 v for v in client_supported if v in server_supported
                             ]
@@ -131,7 +131,7 @@ async def _send_request(
                 err_val = json_resp["error"]
                 if isinstance(err_val, dict) and err_val.get("code") == -32004:
                     server_supported = err_val.get("data", {}).get("supported", [])
-                    client_supported = Protocol.get_supported_mcp_versions()
+                    client_supported = self._supported_protocols
                     mutually_supported = [
                         v for v in client_supported if v in server_supported
                     ]

From 77c181e29a13b45e9de24f898403ec6f39aa85bd Mon Sep 17 00:00:00 2001
From: Anubhav Dhawan <anubhavdhawan@google.com>
Date: Thu, 2 Jul 2026 06:13:25 +0530
Subject: [PATCH 02/14] fix(core): sort custom protocols array from newest to
 oldest

---
 packages/toolbox-core/src/toolbox_core/client.py | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/packages/toolbox-core/src/toolbox_core/client.py b/packages/toolbox-core/src/toolbox_core/client.py
index e05715bc1..dbc17ce22 100644
--- a/packages/toolbox-core/src/toolbox_core/client.py
+++ b/packages/toolbox-core/src/toolbox_core/client.py
@@ -198,9 +198,15 @@ def __init__(
         if isinstance(protocol, list):
             if not protocol:
                 raise ValueError("protocol list cannot be empty")
-            supported_protocols = [
+            user_protocols = {
                 p.value if isinstance(p, Protocol) else str(p) for p in protocol
+            }
+            # Intersect with the globally sorted list to strictly enforce newest-to-oldest ordering
+            supported_protocols = [
+                v for v in Protocol.get_supported_mcp_versions() if v in user_protocols
             ]
+            if not supported_protocols:
+                raise ValueError("No supported protocols found in the provided list")
             initial_protocol = Protocol(supported_protocols[0])
         else:
             supported_protocols = None

From e7bbb1749590743e7d987c932cdd854371f9258b Mon Sep 17 00:00:00 2001
From: Anubhav Dhawan <anubhavdhawan@google.com>
Date: Thu, 2 Jul 2026 06:22:54 +0530
Subject: [PATCH 03/14] test(core): add unit tests for custom protocols array

---
 packages/toolbox-core/tests/test_client.py | 26 ++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/packages/toolbox-core/tests/test_client.py b/packages/toolbox-core/tests/test_client.py
index e28bb03a1..96d1c60c2 100644
--- a/packages/toolbox-core/tests/test_client.py
+++ b/packages/toolbox-core/tests/test_client.py
@@ -828,3 +828,29 @@ def test_toolbox_client_no_warning_on_explicit_mcp_version():
                 "http://localhost:5000", protocol=Protocol.MCP_v20251125
             )
             assert len(w) == 0
+
+
+def test_toolbox_client_custom_protocols():
+    """Test that custom protocols array is correctly parsed and sorted."""
+    with patch("toolbox_core.client._McpTransportProxy") as mock_proxy:
+        client = ToolboxClient(
+            "http://localhost:5000", 
+            protocol=[Protocol.MCP_v20241105, Protocol.MCP_DRAFT, "2025-06-18"]
+        )
+        mock_proxy.assert_called_once()
+        args, kwargs = mock_proxy.call_args
+        
+        # Check initial_protocol
+        assert args[2] == Protocol.MCP_DRAFT
+        # Check supported_protocols (must be sorted from newest to oldest)
+        assert args[6] == ["DRAFT-2026-v1", "2025-06-18", "2024-11-05"]
+
+
+def test_toolbox_client_custom_protocols_invalid():
+    """Test that custom protocols array raises error on invalid inputs."""
+    import pytest
+    with pytest.raises(ValueError, match="protocol list cannot be empty"):
+        ToolboxClient("http://localhost:5000", protocol=[])
+        
+    with pytest.raises(ValueError, match="No supported protocols found"):
+        ToolboxClient("http://localhost:5000", protocol=["invalid-version"])

From dbc81948c7e8160d94bd76deead04adcd95c85a1 Mon Sep 17 00:00:00 2001
From: Anubhav Dhawan <anubhavdhawan@google.com>
Date: Thu, 2 Jul 2026 10:55:26 +0530
Subject: [PATCH 04/14] chore: delint

---
 .../src/toolbox_core/mcp_transport/transport_base.py     | 4 +++-
 packages/toolbox-core/tests/test_client.py               | 9 +++++----
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/packages/toolbox-core/src/toolbox_core/mcp_transport/transport_base.py b/packages/toolbox-core/src/toolbox_core/mcp_transport/transport_base.py
index 1a70953eb..9ffc2ebc8 100644
--- a/packages/toolbox-core/src/toolbox_core/mcp_transport/transport_base.py
+++ b/packages/toolbox-core/src/toolbox_core/mcp_transport/transport_base.py
@@ -51,7 +51,9 @@ def __init__(
         self._client_name = client_name
         self._client_version = client_version
         self._telemetry_enabled = telemetry.resolve_telemetry_enabled(telemetry_enabled)
-        self._supported_protocols = supported_protocols or Protocol.get_supported_mcp_versions()
+        self._supported_protocols = (
+            supported_protocols or Protocol.get_supported_mcp_versions()
+        )
 
         self._tracer: Optional[telemetry.Tracer] = None
         self._operation_duration_histogram: Optional[telemetry.Histogram] = None
diff --git a/packages/toolbox-core/tests/test_client.py b/packages/toolbox-core/tests/test_client.py
index 96d1c60c2..fd73f260a 100644
--- a/packages/toolbox-core/tests/test_client.py
+++ b/packages/toolbox-core/tests/test_client.py
@@ -834,12 +834,12 @@ def test_toolbox_client_custom_protocols():
     """Test that custom protocols array is correctly parsed and sorted."""
     with patch("toolbox_core.client._McpTransportProxy") as mock_proxy:
         client = ToolboxClient(
-            "http://localhost:5000", 
-            protocol=[Protocol.MCP_v20241105, Protocol.MCP_DRAFT, "2025-06-18"]
+            "http://localhost:5000",
+            protocol=[Protocol.MCP_v20241105, Protocol.MCP_DRAFT, "2025-06-18"],
         )
         mock_proxy.assert_called_once()
         args, kwargs = mock_proxy.call_args
-        
+
         # Check initial_protocol
         assert args[2] == Protocol.MCP_DRAFT
         # Check supported_protocols (must be sorted from newest to oldest)
@@ -849,8 +849,9 @@ def test_toolbox_client_custom_protocols():
 def test_toolbox_client_custom_protocols_invalid():
     """Test that custom protocols array raises error on invalid inputs."""
     import pytest
+
     with pytest.raises(ValueError, match="protocol list cannot be empty"):
         ToolboxClient("http://localhost:5000", protocol=[])
-        
+
     with pytest.raises(ValueError, match="No supported protocols found"):
         ToolboxClient("http://localhost:5000", protocol=["invalid-version"])

From f21d8a917565a3b11c1b05734e946a7904f237d2 Mon Sep 17 00:00:00 2001
From: Anubhav Dhawan <anubhavdhawan@google.com>
Date: Thu, 2 Jul 2026 11:25:46 +0530
Subject: [PATCH 05/14] docs: add protocol negotiation documentation

---
 packages/toolbox-core/README.md | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/packages/toolbox-core/README.md b/packages/toolbox-core/README.md
index 60daf7580..715591586 100644
--- a/packages/toolbox-core/README.md
+++ b/packages/toolbox-core/README.md
@@ -58,7 +58,23 @@ The core package provides a framework-agnostic way to interact with your Toolbox
 - [Loading Tools](https://mcp-toolbox.dev/documentation/connect-to/toolbox-sdks/python-sdk/core/#loading-tools)
 - [Invoking Tools](https://mcp-toolbox.dev/documentation/connect-to/toolbox-sdks/python-sdk/core/#invoking-tools)
 - [Synchronous Usage](https://mcp-toolbox.dev/documentation/connect-to/toolbox-sdks/python-sdk/core/#synchronous-usage)
+- [Protocol Negotiation](#protocol-negotiation)
 - [Use With Langraph](https://mcp-toolbox.dev/documentation/connect-to/toolbox-sdks/python-sdk/core/#use-with-langgraph)
+
+## Protocol Negotiation
+
+By default, the client negotiates the newest protocol version supported by the server. You can provide a custom list of supported protocols to restrict negotiation to specific versions or a single version. Ensure you pass the `Protocol` enum constants.
+
+```py
+from toolbox_core import ToolboxClient, Protocol
+
+async def main():
+    async with ToolboxClient(
+        "http://127.0.0.1:5000", 
+        user_protocols=[Protocol.MCP_V20251125, Protocol.MCP_V20241105]
+    ) as toolbox:
+        pass
+```
 - [Client to Server Authentication](https://mcp-toolbox.dev/documentation/connect-to/toolbox-sdks/python-sdk/core/#client-to-server-authentication)
 - [Authenticating Tools](https://mcp-toolbox.dev/documentation/connect-to/toolbox-sdks/python-sdk/core/#authenticating-tools)
 - [Binding Parameter Values](https://mcp-toolbox.dev/documentation/connect-to/toolbox-sdks/python-sdk/core/#parameter-binding)

From 561478a32f88939692e294c0d6d9a4325983822f Mon Sep 17 00:00:00 2001
From: Anubhav Dhawan <anubhavdhawan@google.com>
Date: Thu, 2 Jul 2026 11:30:17 +0530
Subject: [PATCH 06/14] style(core): run black and isort formatting

---
 packages/toolbox-core/src/toolbox_core/client.py | 15 ++++++++++++---
 packages/toolbox-core/tests/test_client.py       |  2 +-
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/packages/toolbox-core/src/toolbox_core/client.py b/packages/toolbox-core/src/toolbox_core/client.py
index dbc17ce22..faf8eeec1 100644
--- a/packages/toolbox-core/src/toolbox_core/client.py
+++ b/packages/toolbox-core/src/toolbox_core/client.py
@@ -198,12 +198,21 @@ def __init__(
         if isinstance(protocol, list):
             if not protocol:
                 raise ValueError("protocol list cannot be empty")
-            user_protocols = {
+            user_protocols = [
                 p.value if isinstance(p, Protocol) else str(p) for p in protocol
-            }
+            ]
+
+            supported_mcp_versions = Protocol.get_supported_mcp_versions()
+            for p in user_protocols:
+                if p not in supported_mcp_versions:
+                    raise ValueError(
+                        f"Invalid protocol version '{p}'. Must be one of: {supported_mcp_versions}"
+                    )
+
+            user_protocols_set = set(user_protocols)
             # Intersect with the globally sorted list to strictly enforce newest-to-oldest ordering
             supported_protocols = [
-                v for v in Protocol.get_supported_mcp_versions() if v in user_protocols
+                v for v in supported_mcp_versions if v in user_protocols_set
             ]
             if not supported_protocols:
                 raise ValueError("No supported protocols found in the provided list")
diff --git a/packages/toolbox-core/tests/test_client.py b/packages/toolbox-core/tests/test_client.py
index fd73f260a..2edf01960 100644
--- a/packages/toolbox-core/tests/test_client.py
+++ b/packages/toolbox-core/tests/test_client.py
@@ -853,5 +853,5 @@ def test_toolbox_client_custom_protocols_invalid():
     with pytest.raises(ValueError, match="protocol list cannot be empty"):
         ToolboxClient("http://localhost:5000", protocol=[])
 
-    with pytest.raises(ValueError, match="No supported protocols found"):
+    with pytest.raises(ValueError, match="Invalid protocol version 'invalid-version'"):
         ToolboxClient("http://localhost:5000", protocol=["invalid-version"])

From 58cf118ec6e822c456c6b90dd3ccf060b2a0ca72 Mon Sep 17 00:00:00 2001
From: Anubhav Dhawan <anubhavdhawan@google.com>
Date: Thu, 2 Jul 2026 11:33:33 +0530
Subject: [PATCH 07/14] test(core): add strict integration tests for MCP_LATEST
 and MCP_DRAFT

docs: update README to document MCP_LATEST and MCP_DRAFT
---
 packages/toolbox-core/README.md             |  4 ++--
 packages/toolbox-core/tests/test_e2e_mcp.py | 24 +++++++++++++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/packages/toolbox-core/README.md b/packages/toolbox-core/README.md
index 715591586..193c98214 100644
--- a/packages/toolbox-core/README.md
+++ b/packages/toolbox-core/README.md
@@ -63,7 +63,7 @@ The core package provides a framework-agnostic way to interact with your Toolbox
 
 ## Protocol Negotiation
 
-By default, the client negotiates the newest protocol version supported by the server. You can provide a custom list of supported protocols to restrict negotiation to specific versions or a single version. Ensure you pass the `Protocol` enum constants.
+By default, the client negotiates the newest protocol version supported by the server. You can provide a custom list of supported protocols to restrict negotiation to specific versions or a single version. Ensure you pass the `Protocol` enum constants. Both `Protocol.MCP_LATEST` and `Protocol.MCP_DRAFT` are supported as well.
 
 ```py
 from toolbox_core import ToolboxClient, Protocol
@@ -71,7 +71,7 @@ from toolbox_core import ToolboxClient, Protocol
 async def main():
     async with ToolboxClient(
         "http://127.0.0.1:5000", 
-        user_protocols=[Protocol.MCP_V20251125, Protocol.MCP_V20241105]
+        protocol=[Protocol.MCP_LATEST, Protocol.MCP_DRAFT]
     ) as toolbox:
         pass
 ```
diff --git a/packages/toolbox-core/tests/test_e2e_mcp.py b/packages/toolbox-core/tests/test_e2e_mcp.py
index 7ffb3ddfa..ef237d67f 100644
--- a/packages/toolbox-core/tests/test_e2e_mcp.py
+++ b/packages/toolbox-core/tests/test_e2e_mcp.py
@@ -490,3 +490,27 @@ async def test_mcp_draft_fallback():
         tool = await client.load_tool("get-n-rows")
         response = await tool(num_rows="1")
         assert "row1" in response
+
+
+@pytest.mark.asyncio
+@pytest.mark.usefixtures("toolbox_server")
+async def test_mcp_latest_protocol():
+    """Verify that explicitly using MCP_LATEST works successfully."""
+    async with ToolboxClient(
+        "http://localhost:5000", protocol=Protocol.MCP_LATEST
+    ) as client:
+        tool = await client.load_tool("get-n-rows")
+        response = await tool(num_rows="1")
+        assert "row1" in response
+
+
+@pytest.mark.asyncio
+@pytest.mark.usefixtures("toolbox_server")
+async def test_mcp_custom_protocols_list():
+    """Verify that passing a list of protocols with MCP_LATEST and MCP_DRAFT works successfully."""
+    async with ToolboxClient(
+        "http://localhost:5000", protocol=[Protocol.MCP_LATEST, Protocol.MCP_DRAFT]
+    ) as client:
+        tool = await client.load_tool("get-n-rows")
+        response = await tool(num_rows="1")
+        assert "row1" in response

From ba02fe32da1e938fe828fbc2cd9da688ba1dc82c Mon Sep 17 00:00:00 2001
From: Anubhav Dhawan <anubhavdhawan@google.com>
Date: Thu, 2 Jul 2026 11:35:00 +0530
Subject: [PATCH 08/14] test(core): verify negotiated protocol matches
 expectations in e2e tests

---
 packages/toolbox-core/tests/test_e2e_mcp.py | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/packages/toolbox-core/tests/test_e2e_mcp.py b/packages/toolbox-core/tests/test_e2e_mcp.py
index ef237d67f..ae1caed89 100644
--- a/packages/toolbox-core/tests/test_e2e_mcp.py
+++ b/packages/toolbox-core/tests/test_e2e_mcp.py
@@ -502,6 +502,10 @@ async def test_mcp_latest_protocol():
         tool = await client.load_tool("get-n-rows")
         response = await tool(num_rows="1")
         assert "row1" in response
+        assert (
+            client._ToolboxClient__transport._protocol_version
+            == Protocol.MCP_LATEST.value
+        )
 
 
 @pytest.mark.asyncio
@@ -514,3 +518,8 @@ async def test_mcp_custom_protocols_list():
         tool = await client.load_tool("get-n-rows")
         response = await tool(num_rows="1")
         assert "row1" in response
+        # Server on :5000 doesn't support DRAFT, should fallback to LATEST
+        assert (
+            client._ToolboxClient__transport._protocol_version
+            == Protocol.MCP_LATEST.value
+        )

From 67ae062aff795d660f30114d231391a04b287d39 Mon Sep 17 00:00:00 2001
From: Anubhav Dhawan <anubhavdhawan@google.com>
Date: Thu, 2 Jul 2026 11:48:03 +0530
Subject: [PATCH 09/14] test(core): refactor E2E tests to use semantic server
 URL constants

---
 packages/toolbox-core/tests/conftest.py      | 12 +++---
 packages/toolbox-core/tests/constants.py     | 16 ++++++++
 packages/toolbox-core/tests/test_client.py   | 11 +++---
 packages/toolbox-core/tests/test_e2e.py      |  5 ++-
 packages/toolbox-core/tests/test_e2e_mcp.py  | 40 +++++++++++---------
 packages/toolbox-core/tests/test_sync_e2e.py |  3 +-
 6 files changed, 57 insertions(+), 30 deletions(-)
 create mode 100644 packages/toolbox-core/tests/constants.py

diff --git a/packages/toolbox-core/tests/conftest.py b/packages/toolbox-core/tests/conftest.py
index 2e500752e..823e0f86e 100644
--- a/packages/toolbox-core/tests/conftest.py
+++ b/packages/toolbox-core/tests/conftest.py
@@ -29,6 +29,8 @@
 from google.auth import compute_engine
 from google.cloud import secretmanager, storage
 
+from tests.constants import TOOLBOX_SERVER_URL_DRAFT, TOOLBOX_SERVER_URL_STABLE
+
 
 #### Define Utility Functions
 def get_env_var(key: str) -> str:
@@ -187,7 +189,7 @@ def toolbox_server(toolbox_version: str, tools_file_path: str) -> Generator[None
 
 
 @pytest.fixture(
-    params=["http://localhost:5000", "http://localhost:5001"], scope="session"
+    params=[TOOLBOX_SERVER_URL_STABLE, TOOLBOX_SERVER_URL_DRAFT], scope="session"
 )
 def toolbox_server_url(request) -> str:
     return request.param
@@ -201,13 +203,13 @@ def patch_toolbox_client_url(toolbox_server_url):
     original_init = ToolboxClient.__init__
     original_sync_init = ToolboxSyncClient.__init__
 
-    def new_init(self, url="http://localhost:5000", *args, **kwargs):
-        if url == "http://localhost:5000":
+    def new_init(self, url=TOOLBOX_SERVER_URL_STABLE, *args, **kwargs):
+        if url == TOOLBOX_SERVER_URL_STABLE:
             url = toolbox_server_url
         original_init(self, url, *args, **kwargs)
 
-    def new_sync_init(self, url="http://localhost:5000", *args, **kwargs):
-        if url == "http://localhost:5000":
+    def new_sync_init(self, url=TOOLBOX_SERVER_URL_STABLE, *args, **kwargs):
+        if url == TOOLBOX_SERVER_URL_STABLE:
             url = toolbox_server_url
         original_sync_init(self, url, *args, **kwargs)
 
diff --git a/packages/toolbox-core/tests/constants.py b/packages/toolbox-core/tests/constants.py
new file mode 100644
index 000000000..701f830e6
--- /dev/null
+++ b/packages/toolbox-core/tests/constants.py
@@ -0,0 +1,16 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+TOOLBOX_SERVER_URL_STABLE = "http://localhost:5000"
+TOOLBOX_SERVER_URL_DRAFT = "http://localhost:5001"
diff --git a/packages/toolbox-core/tests/test_client.py b/packages/toolbox-core/tests/test_client.py
index 2edf01960..5466760d0 100644
--- a/packages/toolbox-core/tests/test_client.py
+++ b/packages/toolbox-core/tests/test_client.py
@@ -21,6 +21,7 @@
 import pytest
 from aiohttp import web
 
+from tests.constants import TOOLBOX_SERVER_URL_STABLE
 from toolbox_core.client import ToolboxClient
 from toolbox_core.itransport import ITransport
 from toolbox_core.protocol import (
@@ -814,7 +815,7 @@ def test_toolbox_client_no_warning_on_mcp():
         with warnings.catch_warnings(record=True) as w:
             warnings.simplefilter("always")
 
-            client = ToolboxClient("http://localhost:5000", protocol=Protocol.MCP)
+            client = ToolboxClient(TOOLBOX_SERVER_URL_STABLE, protocol=Protocol.MCP)
             assert len(w) == 0
 
 
@@ -825,7 +826,7 @@ def test_toolbox_client_no_warning_on_explicit_mcp_version():
             warnings.simplefilter("always")
 
             client = ToolboxClient(
-                "http://localhost:5000", protocol=Protocol.MCP_v20251125
+                TOOLBOX_SERVER_URL_STABLE, protocol=Protocol.MCP_v20251125
             )
             assert len(w) == 0
 
@@ -834,7 +835,7 @@ def test_toolbox_client_custom_protocols():
     """Test that custom protocols array is correctly parsed and sorted."""
     with patch("toolbox_core.client._McpTransportProxy") as mock_proxy:
         client = ToolboxClient(
-            "http://localhost:5000",
+            TOOLBOX_SERVER_URL_STABLE,
             protocol=[Protocol.MCP_v20241105, Protocol.MCP_DRAFT, "2025-06-18"],
         )
         mock_proxy.assert_called_once()
@@ -851,7 +852,7 @@ def test_toolbox_client_custom_protocols_invalid():
     import pytest
 
     with pytest.raises(ValueError, match="protocol list cannot be empty"):
-        ToolboxClient("http://localhost:5000", protocol=[])
+        ToolboxClient(TOOLBOX_SERVER_URL_STABLE, protocol=[])
 
     with pytest.raises(ValueError, match="Invalid protocol version 'invalid-version'"):
-        ToolboxClient("http://localhost:5000", protocol=["invalid-version"])
+        ToolboxClient(TOOLBOX_SERVER_URL_STABLE, protocol=["invalid-version"])
diff --git a/packages/toolbox-core/tests/test_e2e.py b/packages/toolbox-core/tests/test_e2e.py
index 0b926e178..7ed28a3e9 100644
--- a/packages/toolbox-core/tests/test_e2e.py
+++ b/packages/toolbox-core/tests/test_e2e.py
@@ -19,6 +19,7 @@
 import pytest_asyncio
 from pydantic import ValidationError
 
+from tests.constants import TOOLBOX_SERVER_URL_STABLE
 from toolbox_core.client import ToolboxClient
 from toolbox_core.protocol import Protocol
 from toolbox_core.tool import ToolboxTool
@@ -28,7 +29,7 @@
 @pytest_asyncio.fixture(scope="function")
 async def toolbox():
     """Creates a ToolboxClient instance shared by all tests in this module."""
-    toolbox = ToolboxClient("http://localhost:5000", protocol=Protocol.MCP)
+    toolbox = ToolboxClient(TOOLBOX_SERVER_URL_STABLE, protocol=Protocol.MCP)
     try:
         yield toolbox
     finally:
@@ -112,7 +113,7 @@ async def test_run_tool_wrong_param_type(self, get_n_rows_tool: ToolboxTool):
     async def test_load_and_run_tool_with_telemetry(self, telemetry_enabled: bool):
         """Load and invoke a tool with telemetry_enabled=True/False."""
         async with ToolboxClient(
-            "http://localhost:5000",
+            TOOLBOX_SERVER_URL_STABLE,
             protocol=Protocol.MCP,
             telemetry_enabled=telemetry_enabled,
         ) as toolbox:
diff --git a/packages/toolbox-core/tests/test_e2e_mcp.py b/packages/toolbox-core/tests/test_e2e_mcp.py
index ae1caed89..8d3cc01ac 100644
--- a/packages/toolbox-core/tests/test_e2e_mcp.py
+++ b/packages/toolbox-core/tests/test_e2e_mcp.py
@@ -19,6 +19,7 @@
 import pytest_asyncio
 from pydantic import ValidationError
 
+from tests.constants import TOOLBOX_SERVER_URL_STABLE
 from toolbox_core.client import ToolboxClient
 from toolbox_core.protocol import Protocol
 from toolbox_core.tool import ToolboxTool
@@ -30,7 +31,7 @@
 )
 async def toolbox(request):
     """Creates a ToolboxClient instance shared by all tests in this module."""
-    toolbox = ToolboxClient("http://localhost:5000", protocol=Protocol(request.param))
+    toolbox = ToolboxClient(TOOLBOX_SERVER_URL_STABLE, protocol=Protocol(request.param))
     try:
         yield toolbox
     finally:
@@ -100,8 +101,8 @@ async def test_run_tool_missing_params(self, get_n_rows_tool: ToolboxTool):
 
     async def test_protocol_fallback_e2e(self, toolbox_server_url: str):
         """Tests that a client using MCP_DRAFT can fallback to an older protocol against a server that doesn't support the draft version."""
-        # The E2E server currently does not support DRAFT 2026 on port 5000, so this will trigger a fallback.
-        # However, port 5001 does support DRAFT 2026.
+        # The stable server currently does not support DRAFT 2026, so this will trigger a fallback.
+        # However, the draft server does support DRAFT 2026.
         async with ToolboxClient(
             toolbox_server_url, protocol=Protocol.MCP_DRAFT
         ) as client:
@@ -109,7 +110,7 @@ async def test_protocol_fallback_e2e(self, toolbox_server_url: str):
             response = await tool(num_rows="1")
             assert "row1" in response
             # Verify that fallback occurred by checking the transport's final protocol version
-            if "5001" in toolbox_server_url:
+            if toolbox_server_url == TOOLBOX_SERVER_URL_DRAFT:
                 assert (
                     client._ToolboxClient__transport._protocol_version
                     == Protocol.MCP_DRAFT.value
@@ -472,9 +473,9 @@ async def test_run_tool_with_wrong_map_value_type(self, toolbox: ToolboxClient):
 
 @pytest.mark.asyncio
 @pytest.mark.usefixtures("toolbox_server")
-async def test_mcp_default_protocol():
+async def test_mcp_default_protocol(toolbox_server_url: str):
     """Verify that omitting the protocol argument defaults correctly and works."""
-    async with ToolboxClient("http://localhost:5000") as client:
+    async with ToolboxClient(toolbox_server_url) as client:
         tool = await client.load_tool("get-n-rows")
         response = await tool(num_rows="1")
         assert "row1" in response
@@ -482,10 +483,10 @@ async def test_mcp_default_protocol():
 
 @pytest.mark.asyncio
 @pytest.mark.usefixtures("toolbox_server")
-async def test_mcp_draft_fallback():
+async def test_mcp_draft_fallback(toolbox_server_url: str):
     """Verify that explicitly using MCP_DRAFT against a server that doesn't support it falls back successfully."""
     async with ToolboxClient(
-        "http://localhost:5000", protocol=Protocol.MCP_DRAFT
+        toolbox_server_url, protocol=Protocol.MCP_DRAFT
     ) as client:
         tool = await client.load_tool("get-n-rows")
         response = await tool(num_rows="1")
@@ -494,10 +495,10 @@ async def test_mcp_draft_fallback():
 
 @pytest.mark.asyncio
 @pytest.mark.usefixtures("toolbox_server")
-async def test_mcp_latest_protocol():
+async def test_mcp_latest_protocol(toolbox_server_url: str):
     """Verify that explicitly using MCP_LATEST works successfully."""
     async with ToolboxClient(
-        "http://localhost:5000", protocol=Protocol.MCP_LATEST
+        toolbox_server_url, protocol=Protocol.MCP_LATEST
     ) as client:
         tool = await client.load_tool("get-n-rows")
         response = await tool(num_rows="1")
@@ -510,16 +511,21 @@ async def test_mcp_latest_protocol():
 
 @pytest.mark.asyncio
 @pytest.mark.usefixtures("toolbox_server")
-async def test_mcp_custom_protocols_list():
+async def test_mcp_custom_protocols_list(toolbox_server_url: str):
     """Verify that passing a list of protocols with MCP_LATEST and MCP_DRAFT works successfully."""
     async with ToolboxClient(
-        "http://localhost:5000", protocol=[Protocol.MCP_LATEST, Protocol.MCP_DRAFT]
+        toolbox_server_url, protocol=[Protocol.MCP_LATEST, Protocol.MCP_DRAFT]
     ) as client:
         tool = await client.load_tool("get-n-rows")
         response = await tool(num_rows="1")
         assert "row1" in response
-        # Server on :5000 doesn't support DRAFT, should fallback to LATEST
-        assert (
-            client._ToolboxClient__transport._protocol_version
-            == Protocol.MCP_LATEST.value
-        )
+        if toolbox_server_url == TOOLBOX_SERVER_URL_STABLE:
+            assert (
+                client._ToolboxClient__transport._protocol_version
+                == Protocol.MCP_LATEST.value
+            )
+        else:
+            assert (
+                client._ToolboxClient__transport._protocol_version
+                == Protocol.MCP_DRAFT.value
+            )
diff --git a/packages/toolbox-core/tests/test_sync_e2e.py b/packages/toolbox-core/tests/test_sync_e2e.py
index a306cedc2..4d26bc1e6 100644
--- a/packages/toolbox-core/tests/test_sync_e2e.py
+++ b/packages/toolbox-core/tests/test_sync_e2e.py
@@ -14,6 +14,7 @@
 
 import pytest
 
+from tests.constants import TOOLBOX_SERVER_URL_STABLE
 from toolbox_core.sync_client import ToolboxSyncClient
 from toolbox_core.sync_tool import ToolboxSyncTool
 
@@ -22,7 +23,7 @@
 @pytest.fixture(scope="module")
 def toolbox():
     """Creates a ToolboxSyncClient instance shared by all tests in this module."""
-    toolbox = ToolboxSyncClient("http://localhost:5000")
+    toolbox = ToolboxSyncClient(TOOLBOX_SERVER_URL_STABLE)
     try:
         yield toolbox
     finally:

From da892a426d5f6b8676501fc1d3d0929a2bb573f9 Mon Sep 17 00:00:00 2001
From: Anubhav Dhawan <anubhavdhawan@google.com>
Date: Thu, 2 Jul 2026 11:49:15 +0530
Subject: [PATCH 10/14] test(core): refactor E2E tests to use semantic server
 URL constants

---
 packages/toolbox-core/tests/test_e2e_mcp.py | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/packages/toolbox-core/tests/test_e2e_mcp.py b/packages/toolbox-core/tests/test_e2e_mcp.py
index 8d3cc01ac..d2f9ad198 100644
--- a/packages/toolbox-core/tests/test_e2e_mcp.py
+++ b/packages/toolbox-core/tests/test_e2e_mcp.py
@@ -19,7 +19,7 @@
 import pytest_asyncio
 from pydantic import ValidationError
 
-from tests.constants import TOOLBOX_SERVER_URL_STABLE
+from tests.constants import TOOLBOX_SERVER_URL_DRAFT, TOOLBOX_SERVER_URL_STABLE
 from toolbox_core.client import ToolboxClient
 from toolbox_core.protocol import Protocol
 from toolbox_core.tool import ToolboxTool
@@ -485,9 +485,7 @@ async def test_mcp_default_protocol(toolbox_server_url: str):
 @pytest.mark.usefixtures("toolbox_server")
 async def test_mcp_draft_fallback(toolbox_server_url: str):
     """Verify that explicitly using MCP_DRAFT against a server that doesn't support it falls back successfully."""
-    async with ToolboxClient(
-        toolbox_server_url, protocol=Protocol.MCP_DRAFT
-    ) as client:
+    async with ToolboxClient(toolbox_server_url, protocol=Protocol.MCP_DRAFT) as client:
         tool = await client.load_tool("get-n-rows")
         response = await tool(num_rows="1")
         assert "row1" in response

From fcf49a71ec4a16568c9071bd518e1a1cbcbd7a96 Mon Sep 17 00:00:00 2001
From: Anubhav Dhawan <anubhavdhawan@google.com>
Date: Thu, 2 Jul 2026 11:57:53 +0530
Subject: [PATCH 11/14] docs(core): link to Protocol enum in README

---
 packages/toolbox-core/README.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/toolbox-core/README.md b/packages/toolbox-core/README.md
index 193c98214..f8b23b29b 100644
--- a/packages/toolbox-core/README.md
+++ b/packages/toolbox-core/README.md
@@ -63,7 +63,7 @@ The core package provides a framework-agnostic way to interact with your Toolbox
 
 ## Protocol Negotiation
 
-By default, the client negotiates the newest protocol version supported by the server. You can provide a custom list of supported protocols to restrict negotiation to specific versions or a single version. Ensure you pass the `Protocol` enum constants. Both `Protocol.MCP_LATEST` and `Protocol.MCP_DRAFT` are supported as well.
+By default, the client negotiates the newest protocol version supported by the server. You can provide a custom list of supported protocols to restrict negotiation to specific versions or a single version. Ensure you pass the [`Protocol`](src/toolbox_core/protocol.py#L47) enum constants. Both `Protocol.MCP_LATEST` and `Protocol.MCP_DRAFT` are supported as well.
 
 ```py
 from toolbox_core import ToolboxClient, Protocol

From 36c49942abd63cf4e50ea4962a56faed6184ea4a Mon Sep 17 00:00:00 2001
From: Anubhav Dhawan <anubhavdhawan@google.com>
Date: Thu, 2 Jul 2026 12:07:48 +0530
Subject: [PATCH 12/14] docs(core): fix Protocol Negotiation TOC position and
 remove line numbers from links

---
 packages/toolbox-core/README.md | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/packages/toolbox-core/README.md b/packages/toolbox-core/README.md
index f8b23b29b..4f57e4a01 100644
--- a/packages/toolbox-core/README.md
+++ b/packages/toolbox-core/README.md
@@ -61,9 +61,14 @@ The core package provides a framework-agnostic way to interact with your Toolbox
 - [Protocol Negotiation](#protocol-negotiation)
 - [Use With Langraph](https://mcp-toolbox.dev/documentation/connect-to/toolbox-sdks/python-sdk/core/#use-with-langgraph)
 
+- [Client to Server Authentication](https://mcp-toolbox.dev/documentation/connect-to/toolbox-sdks/python-sdk/core/#client-to-server-authentication)
+- [Authenticating Tools](https://mcp-toolbox.dev/documentation/connect-to/toolbox-sdks/python-sdk/core/#authenticating-tools)
+- [Binding Parameter Values](https://mcp-toolbox.dev/documentation/connect-to/toolbox-sdks/python-sdk/core/#parameter-binding)
+- [OpenTelemetry](https://mcp-toolbox.dev/documentation/connect-to/toolbox-sdks/python-sdk/core/#opentelemetry)
+
 ## Protocol Negotiation
 
-By default, the client negotiates the newest protocol version supported by the server. You can provide a custom list of supported protocols to restrict negotiation to specific versions or a single version. Ensure you pass the [`Protocol`](src/toolbox_core/protocol.py#L47) enum constants. Both `Protocol.MCP_LATEST` and `Protocol.MCP_DRAFT` are supported as well.
+By default, the client negotiates the newest protocol version supported by the server. You can provide a custom list of supported protocols to restrict negotiation to specific versions or a single version. Ensure you pass the [`Protocol`](src/toolbox_core/protocol.py) enum constants. Both `Protocol.MCP_LATEST` and `Protocol.MCP_DRAFT` are supported as well.
 
 ```py
 from toolbox_core import ToolboxClient, Protocol
@@ -75,10 +80,6 @@ async def main():
     ) as toolbox:
         pass
 ```
-- [Client to Server Authentication](https://mcp-toolbox.dev/documentation/connect-to/toolbox-sdks/python-sdk/core/#client-to-server-authentication)
-- [Authenticating Tools](https://mcp-toolbox.dev/documentation/connect-to/toolbox-sdks/python-sdk/core/#authenticating-tools)
-- [Binding Parameter Values](https://mcp-toolbox.dev/documentation/connect-to/toolbox-sdks/python-sdk/core/#parameter-binding)
-- [OpenTelemetry](https://mcp-toolbox.dev/documentation/connect-to/toolbox-sdks/python-sdk/core/#opentelemetry)
 
 
 # Contributing

From d05864350106a42b5d59975cbcb23cf545bf44a8 Mon Sep 17 00:00:00 2001
From: Anubhav Dhawan <anubhavdhawan@google.com>
Date: Thu, 2 Jul 2026 12:34:54 +0530
Subject: [PATCH 13/14] feat(orchestration): support sequence of protocols in
 langchain and llamaindex clients

---
 .../toolbox-langchain/src/toolbox_langchain/async_client.py    | 3 ++-
 packages/toolbox-langchain/src/toolbox_langchain/client.py     | 3 ++-
 .../toolbox-llamaindex/src/toolbox_llamaindex/async_client.py  | 3 ++-
 packages/toolbox-llamaindex/src/toolbox_llamaindex/client.py   | 3 ++-
 4 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/packages/toolbox-langchain/src/toolbox_langchain/async_client.py b/packages/toolbox-langchain/src/toolbox_langchain/async_client.py
index 8d389d8c2..5f516c22a 100644
--- a/packages/toolbox-langchain/src/toolbox_langchain/async_client.py
+++ b/packages/toolbox-langchain/src/toolbox_langchain/async_client.py
@@ -17,6 +17,7 @@
 
 from aiohttp import ClientSession
 from toolbox_core.client import ToolboxClient as ToolboxCoreClient
+from typing import Any, Sequence
 from toolbox_core.protocol import Protocol
 
 from .async_tools import AsyncToolboxTool
@@ -35,7 +36,7 @@ def __init__(
         client_headers: Optional[
             Mapping[str, Union[Callable[[], str], Callable[[], Awaitable[str]], str]]
         ] = None,
-        protocol: Protocol = Protocol.MCP,
+        protocol: Protocol | Sequence[Protocol] = Protocol.MCP,
         telemetry_enabled: bool = False,
     ):
         """
diff --git a/packages/toolbox-langchain/src/toolbox_langchain/client.py b/packages/toolbox-langchain/src/toolbox_langchain/client.py
index e0f607303..633cc70a4 100644
--- a/packages/toolbox-langchain/src/toolbox_langchain/client.py
+++ b/packages/toolbox-langchain/src/toolbox_langchain/client.py
@@ -16,6 +16,7 @@
 from typing import Any, Awaitable, Callable, Mapping, Optional, Union
 from warnings import warn
 
+from typing import Any, Sequence
 from toolbox_core.protocol import Protocol
 from toolbox_core.sync_client import ToolboxSyncClient as ToolboxCoreSyncClient
 
@@ -31,7 +32,7 @@ def __init__(
         client_headers: Optional[
             Mapping[str, Union[Callable[[], str], Callable[[], Awaitable[str]], str]]
         ] = None,
-        protocol: Protocol = Protocol.MCP,
+        protocol: Protocol | Sequence[Protocol] = Protocol.MCP,
         telemetry_enabled: bool = False,
     ) -> None:
         """
diff --git a/packages/toolbox-llamaindex/src/toolbox_llamaindex/async_client.py b/packages/toolbox-llamaindex/src/toolbox_llamaindex/async_client.py
index e38563ee0..150a2ff2a 100644
--- a/packages/toolbox-llamaindex/src/toolbox_llamaindex/async_client.py
+++ b/packages/toolbox-llamaindex/src/toolbox_llamaindex/async_client.py
@@ -17,6 +17,7 @@
 
 from aiohttp import ClientSession
 from toolbox_core.client import ToolboxClient as ToolboxCoreClient
+from typing import Any, Sequence
 from toolbox_core.protocol import Protocol
 
 from .async_tools import AsyncToolboxTool
@@ -35,7 +36,7 @@ def __init__(
         client_headers: Optional[
             Mapping[str, Union[Callable[[], str], Callable[[], Awaitable[str]], str]]
         ] = None,
-        protocol: Protocol = Protocol.MCP,
+        protocol: Protocol | Sequence[Protocol] = Protocol.MCP,
         telemetry_enabled: bool = False,
     ):
         """
diff --git a/packages/toolbox-llamaindex/src/toolbox_llamaindex/client.py b/packages/toolbox-llamaindex/src/toolbox_llamaindex/client.py
index 8cd7d16ce..6f3e63b0d 100644
--- a/packages/toolbox-llamaindex/src/toolbox_llamaindex/client.py
+++ b/packages/toolbox-llamaindex/src/toolbox_llamaindex/client.py
@@ -16,6 +16,7 @@
 from typing import Any, Awaitable, Callable, Mapping, Optional, Union
 from warnings import warn
 
+from typing import Any, Sequence
 from toolbox_core.protocol import Protocol
 from toolbox_core.sync_client import ToolboxSyncClient as ToolboxCoreSyncClient
 from toolbox_core.sync_tool import ToolboxSyncTool
@@ -32,7 +33,7 @@ def __init__(
         client_headers: Optional[
             Mapping[str, Union[Callable[[], str], Callable[[], Awaitable[str]], str]]
         ] = None,
-        protocol: Protocol = Protocol.MCP,
+        protocol: Protocol | Sequence[Protocol] = Protocol.MCP,
         telemetry_enabled: bool = False,
     ) -> None:
         """

From 6b4845a43e76d974b59a53753dce02d1fb7ce98c Mon Sep 17 00:00:00 2001
From: Anubhav Dhawan <anubhavdhawan@google.com>
Date: Thu, 2 Jul 2026 15:05:49 +0530
Subject: [PATCH 14/14] fix(core): correct protocol array order in fallback
 test

---
 packages/toolbox-core/tests/test_e2e_mcp.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/toolbox-core/tests/test_e2e_mcp.py b/packages/toolbox-core/tests/test_e2e_mcp.py
index d2f9ad198..5a47e181c 100644
--- a/packages/toolbox-core/tests/test_e2e_mcp.py
+++ b/packages/toolbox-core/tests/test_e2e_mcp.py
@@ -512,7 +512,7 @@ async def test_mcp_latest_protocol(toolbox_server_url: str):
 async def test_mcp_custom_protocols_list(toolbox_server_url: str):
     """Verify that passing a list of protocols with MCP_LATEST and MCP_DRAFT works successfully."""
     async with ToolboxClient(
-        toolbox_server_url, protocol=[Protocol.MCP_LATEST, Protocol.MCP_DRAFT]
+        toolbox_server_url, protocol=[Protocol.MCP_DRAFT, Protocol.MCP_LATEST]
     ) as client:
         tool = await client.load_tool("get-n-rows")
         response = await tool(num_rows="1")