Hermes MCP Server Extnsn

Hermes MCP Server Extension

When to Use

When you need external agents (Codex, Windsurf, Claude Code, Cursor) to access Hermes capabilities via MCP. The MCP server (mcp_serve.py) is separate from the agent's internal tool registry (tools/).

Key File

~/.hermes/hermes-agent/mcp_serve.py

Architecture

Hermes Internal Tools (tools/*.py)
  └── Only available to Hermes's own agent loop
  └── Registered via tools/registry.py

Hermes MCP Server (mcp_serve.py)
  └── Available to any MCP client (Codex, Windsurf, CC)
  └── Uses @mcp.tool() decorator inside create_mcp_server()
  └── Separate from internal tools — must reimplement or import helpers

Adding an MCP Tool

# Inside create_mcp_server() in mcp_serve.py:

# 1. Define helpers (reuse internals or reimplement)
def _get_skills_dir() -> Path:
    try:
        from hermes_constants import get_hermes_home
        return get_hermes_home() / "skills"
    except ImportError:
        return Path(os.environ.get("HERMES_HOME", Path.home() / ".hermes")) / "skills"

# 2. Add tool with @mcp.tool() decorator
@mcp.tool()
def my_new_tool(param: str) -> str:
    """Description visible to MCP clients.

    Args:
        param: What this parameter does.
    """
    return json.dumps({"result": "..."}, ensure_ascii=False)

Current MCP Tools (15)

Messaging (10)

• conversations_list, conversation_get, messages_read, attachments_fetch
• events_poll, events_wait, messages_send, channels_list
• permissions_list_open, permissions_respond

Skills & Routing (5)

• skill_list — list all skills with metadata (name, desc, category, tags)
• skill_view — load full SKILL.md content + linked files
• skill_route — match task description against routing triggers (Chinese + English)
• routing_rules — return full skill-router.md content
• skill_apply — ONE-STEP: find + load skill by name or task description. USE THIS FIRST.

Governance Feedback Loop (2)

• governance_submit_candidate — save external-agent findings as governance candidates
• governance_list_candidates — inspect recent saved candidates in the governance inbox

Auto-Routing Architecture (Critical)

External agents (Codex, Windsurf, CC) don't know to call skill tools unless told. Solution: embed the routing table in FastMCP(instructions=...) so it's always visible.

# At startup, read skill-router.md and build instructions dynamically
_routing_text = ""
_router_path = Path(HERMES_HOME) / "routing" / "skill-router.md"
for line in _router_path.read_text().splitlines():
    line = line.strip()
    if line.startswith("-") and "→" in line:
        _routing_text += "  " + line.lstrip("- ") + "\n"

mcp = FastMCP("hermes", instructions=(
    "ROUTING TABLE (keywords → skill):\n" + _routing_text +
    "\nCall skill_apply(query) to load a skill. USE THIS FIRST.\n"
))

Why this matters:

• Without routing in instructions, agents only see tool names/descriptions
• With routing in instructions, agents see "古法编程 → old-code" and know to call skill_apply
• skill_apply description says "USE THIS FIRST for any task" — nudges agents to check skills

skill_apply flow:

1. Try direct name match → load SKILL.md
2. Route match against triggers → load top hit
3. Fuzzy fallback on descriptions → load top hit
4. Return full content + source + all_matches

Pitfalls

• yaml import: Import once per function, not inside loops (895 skills = 895 imports)
• Unicode: Use ensure_ascii=False in all json.dumps calls
• Missing deps: Wrap imports in try/except ImportError
• instructions: Update FastMCP(instructions=...) when adding tools
• Circular imports: Can't always import from tools/ — may need to reimplement helpers
• Security scan: hermes-agent skill blocks edits due to env var refs; use this skill instead
• Auto-routing gap: If routing table is NOT in instructions, external agents won't know to call skill tools. Always embed routing triggers in instructions.
• skill_apply > skill_route + skill_view: Two-step flow requires agent to know both tools. skill_apply does it in one call — always prefer it in tool descriptions.
• Routing table size: 105 triggers ≈ 5.7KB in instructions. Acceptable for MCP context.

Decision Guide

Files Modified

• mcp_serve.py — added skill_list, skill_view, skill_route, routing_rules, skill_apply tools
• FastMCP instructions updated: routing table from skill-router.md embedded at startup
• _routing_text built dynamically from ~/.hermes/routing/skill-router.md
• _scan_skills() helper: walks skills dir, parses frontmatter, returns metadata
• _route_skill() helper: matches query against routing triggers + fuzzy fallback
• _load_skill_content() helper: finds and reads SKILL.md by name

Standalone Package: mcp-skill-hub

The same architecture can be extracted as a standalone package for others to use. Location: /tmp/mcp-skill-hub/ (ready to push to GitHub).

mcp-skill-hub/
├── pyproject.toml              # pip install mcp-skill-hub
├── src/mcp_skill_hub/
│   └── server.py               # standalone: no Hermes deps
└── examples/skills/
    ├── router.md               # keyword → skill routing
    ├── ddd-project/SKILL.md
    ├── code-review/SKILL.md
    └── old-code/SKILL.md

Architecture Insight (for README / talks)

The core idea is portable agent knowledge:

SKILL.md  = reusable knowledge unit (markdown, human-editable, agent-executable)
router.md = keyword → skill mapping (Chinese + English triggers)
MCP       = sharing protocol (one server, any client)

• Skills are just markdown — no code, no API, no cloud
• Anyone can contribute by PR-ing a SKILL.md
• Routing table in MCP instructions = agents auto-discover skills
• skill_apply("古法编程") one-step = zero-friction skill loading
• Tagline: "Share AI agent skills as markdown via MCP"

Why This Matters

Without this pattern:

• Agent knowledge is locked in system prompts / config files
• Switching agents means losing all learned workflows
• No way to share proven workflows between agents

With this pattern:

• Skills are portable across any MCP-capable agent
• Community can contribute skills via git
• Routing is declarative (keywords in router.md)
• One skill_apply() call replaces hours of trial-and-error