diff --git a/hermes_cli/tools_config.py b/hermes_cli/tools_config.py
index f12a4b39722..4946a7c8fa6 100644
--- a/hermes_cli/tools_config.py
+++ b/hermes_cli/tools_config.py
@@ -354,9 +354,24 @@ def _get_platform_tools(config: dict, platform: str) -> Set[str]:
 
 
 def _save_platform_tools(config: dict, platform: str, enabled_toolset_keys: Set[str]):
-    """Save the selected toolset keys for a platform to config."""
+    """Save the selected toolset keys for a platform to config.
+
+    Preserve dynamic MCP toolsets (``mcp-<server>``) that were already set for
+    the platform. These entries are not exposed in the tools configurator UI,
+    but they should survive when the user changes the configurable toolsets.
+    """
     config.setdefault("platform_toolsets", {})
-    config["platform_toolsets"][platform] = sorted(enabled_toolset_keys)
+
+    existing_toolsets = config.get("platform_toolsets", {}).get(platform, [])
+    if not isinstance(existing_toolsets, list):
+        existing_toolsets = []
+
+    preserved_entries = {
+        entry for entry in existing_toolsets
+        if isinstance(entry, str) and entry.startswith("mcp-")
+    }
+
+    config["platform_toolsets"][platform] = sorted(enabled_toolset_keys | preserved_entries)
     save_config(config)
 
 
diff --git a/tests/hermes_cli/test_tools_config.py b/tests/hermes_cli/test_tools_config.py
index 92e1e60c30c..441181c14c7 100644
--- a/tests/hermes_cli/test_tools_config.py
+++ b/tests/hermes_cli/test_tools_config.py
@@ -1,6 +1,13 @@
 """Tests for hermes_cli.tools_config platform tool persistence."""
 
-from hermes_cli.tools_config import _get_platform_tools, _platform_toolset_summary, _toolset_has_keys
+from unittest.mock import patch
+
+from hermes_cli.tools_config import (
+    _get_platform_tools,
+    _platform_toolset_summary,
+    _save_platform_tools,
+    _toolset_has_keys,
+)
 
 
 def test_get_platform_tools_uses_default_when_platform_not_configured():
@@ -31,7 +38,7 @@ def test_platform_toolset_summary_uses_explicit_platform_list():
 def test_toolset_has_keys_for_vision_accepts_codex_auth(tmp_path, monkeypatch):
     monkeypatch.setenv("HERMES_HOME", str(tmp_path))
     (tmp_path / "auth.json").write_text(
-        '{"active_provider":"openai-codex","providers":{"openai-codex":{"tokens":{"access_token":"codex-access-token","refresh_token":"codex-refresh-token"}}}}'
+        '{"active_provider":"openai-codex","providers":{"openai-codex":{"tokens":{"access_token": "codex-...oken","refresh_token": "codex-...oken"}}}}'
     )
     monkeypatch.delenv("OPENROUTER_API_KEY", raising=False)
     monkeypatch.delenv("OPENAI_BASE_URL", raising=False)
@@ -40,3 +47,70 @@ def test_toolset_has_keys_for_vision_accepts_codex_auth(tmp_path, monkeypatch):
     monkeypatch.delenv("CONTEXT_VISION_PROVIDER", raising=False)
 
     assert _toolset_has_keys("vision") is True
+
+
+def test_save_platform_tools_preserves_dynamic_mcp_toolsets():
+    """Dynamic MCP toolsets should survive platform tool reconfiguration."""
+    config = {
+        "platform_toolsets": {
+            "cli": ["web", "terminal", "mcp-time", "mcp-github", "mcp-custom-server"]
+        }
+    }
+
+    new_selection = {"web", "browser"}
+
+    with patch("hermes_cli.tools_config.save_config"):
+        _save_platform_tools(config, "cli", new_selection)
+
+    saved_toolsets = config["platform_toolsets"]["cli"]
+
+    assert "mcp-time" in saved_toolsets
+    assert "mcp-github" in saved_toolsets
+    assert "mcp-custom-server" in saved_toolsets
+    assert "web" in saved_toolsets
+    assert "browser" in saved_toolsets
+    assert "terminal" not in saved_toolsets
+
+
+def test_save_platform_tools_does_not_preserve_platform_presets():
+    config = {
+        "platform_toolsets": {
+            "cli": ["hermes-cli", "mcp-time"]
+        }
+    }
+
+    with patch("hermes_cli.tools_config.save_config"):
+        _save_platform_tools(config, "cli", {"web"})
+
+    saved_toolsets = config["platform_toolsets"]["cli"]
+
+    assert "web" in saved_toolsets
+    assert "mcp-time" in saved_toolsets
+    assert "hermes-cli" not in saved_toolsets
+
+
+def test_save_platform_tools_handles_empty_existing_config():
+    config = {}
+
+    with patch("hermes_cli.tools_config.save_config"):
+        _save_platform_tools(config, "telegram", {"web", "terminal"})
+
+    saved_toolsets = config["platform_toolsets"]["telegram"]
+
+    assert "web" in saved_toolsets
+    assert "terminal" in saved_toolsets
+
+
+def test_save_platform_tools_handles_invalid_existing_config():
+    config = {
+        "platform_toolsets": {
+            "cli": "invalid-string-value"
+        }
+    }
+
+    with patch("hermes_cli.tools_config.save_config"):
+        _save_platform_tools(config, "cli", {"web"})
+
+    saved_toolsets = config["platform_toolsets"]["cli"]
+
+    assert saved_toolsets == ["web"]