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feat(tools): add "no_mcp" sentinel to exclude MCP servers per platform

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Currently, MCP servers are included on all platforms by default. If a
platform's toolset list does not explicitly name any MCP servers, every
globally enabled MCP server is injected. There is no way to opt a
platform out of MCP servers entirely.

This matters for the API server platform when used as an execution
backend — each spawned agent session gets the full MCP tool schema
injected into its system prompt, dramatically inflating token usage
(e.g. 57K tokens vs 9K without MCP tools) and slowing response times.

Add a "no_mcp" sentinel value for platform_toolsets. When present in a
platform's toolset list, all MCP servers are excluded for that platform.
Other platforms are unaffected.

Usage in config.yaml:

    platform_toolsets:
      api_server:
        - terminal
        - file
        - web
        - no_mcp    # exclude all MCP servers

The sentinel is filtered out of the final toolset — it does not appear
as an actual toolset name.
This commit is contained in:
Jonathan Barket 2026-04-06 23:03:14 -05:00 • committed by Teknium
parent b9a5e6e247
commit 7fe6782a25
2 changed files with 48 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

12
hermes_cli/tools_config.py
View file

@ -554,6 +554,7 @@ def _get_platform_tools(
# MCP servers are expected to be available on all platforms by default.
# If the platform explicitly lists one or more MCP server names, treat that
# as an allowlist. Otherwise include every globally enabled MCP server.
# Special sentinel: "no_mcp" in the toolset list disables all MCP servers.
mcp_servers = config.get("mcp_servers") or {}
enabled_mcp_servers = {
name
@ -561,10 +562,15 @@ def _get_platform_tools(
if isinstance(server_cfg, dict)
and _parse_enabled_flag(server_cfg.get("enabled", True), default=True)
}
explicit_mcp_servers = explicit_passthrough & enabled_mcp_servers
enabled_toolsets.update(explicit_passthrough - enabled_mcp_servers)
# Allow "no_mcp" sentinel to opt out of all MCP servers for this platform
if "no_mcp" in toolset_names:
explicit_mcp_servers = set()
enabled_toolsets.update(explicit_passthrough - enabled_mcp_servers - {"no_mcp"})
else:
explicit_mcp_servers = explicit_passthrough & enabled_mcp_servers
enabled_toolsets.update(explicit_passthrough - enabled_mcp_servers)
if include_default_mcp_servers:
if explicit_mcp_servers:
if explicit_mcp_servers or "no_mcp" in toolset_names:
enabled_toolsets.update(explicit_mcp_servers)
else:
enabled_toolsets.update(enabled_mcp_servers)

39
tests/hermes_cli/test_tools_config.py
View file

@ -72,6 +72,45 @@ def test_get_platform_tools_keeps_enabled_mcp_servers_with_explicit_builtin_sele
assert "web-search-prime" in enabled
def test_get_platform_tools_no_mcp_sentinel_excludes_all_mcp_servers():
"""The 'no_mcp' sentinel in platform_toolsets excludes all MCP servers."""
config = {
"platform_toolsets": {"cli": ["web", "terminal", "no_mcp"]},
"mcp_servers": {
"exa": {"url": "https://mcp.exa.ai/mcp"},
"web-search-prime": {"url": "https://api.z.ai/api/mcp/web_search_prime/mcp"},
},
}
enabled = _get_platform_tools(config, "cli")
assert "web" in enabled
assert "terminal" in enabled
assert "exa" not in enabled
assert "web-search-prime" not in enabled
assert "no_mcp" not in enabled
def test_get_platform_tools_no_mcp_sentinel_does_not_affect_other_platforms():
"""The 'no_mcp' sentinel only affects the platform it's configured on."""
config = {
"platform_toolsets": {
"api_server": ["web", "terminal", "no_mcp"],
},
"mcp_servers": {
"exa": {"url": "https://mcp.exa.ai/mcp"},
},
}
# api_server should exclude MCP
api_enabled = _get_platform_tools(config, "api_server")
assert "exa" not in api_enabled
# cli (not configured with no_mcp) should include MCP
cli_enabled = _get_platform_tools(config, "cli")
assert "exa" in cli_enabled
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(