Hermes runs one MCP client across every surface, and a second one it does not expose

Kind: nuance · Status: current · Last verified: 2026-11-09 · Clients: hermes-agent, cline, openclaw · Revisions: 2025-11-25

Cline's read established that finding a client's MCP client is not enough — its behaviour splits four ways, by surface and again by transport, with the CLI's stdio path hand-written and four revisions behind the rest. goose's splits by surface on the client name. Hermes is the counter-case, and checking cost the same work.

Every user-facing surface uses the client in tools/mcp_tool.py, which at 9dcf7714 is split across about 25 tools/mcp_tool_* modules: the interactive CLI, the Electron desktop app's backend (Tauri at a24c12d1), the gateway, the TUI gateway, the ACP adapter, the cron scheduler and the web server. No package.json in the repo depends on @modelcontextprotocol/sdk, and a search for a hand-rolled initialize frame in the TypeScript and TSX sources returns nothing, so the desktop app has no client of its own and drives the Python one. Capability answers therefore hold for the whole product, which has not been true of any other multi-surface client read here.

The hand-written initialize frames in the repo are not clients. When a configured URL answers with a non-MCP content type, Hermes POSTs a minimal frame at 2025-03-26 naming itself hermes-probe to decide whether the endpoint speaks MCP at all before raising NonMcpEndpointError. At 9dcf7714 there is a second one: the platform resolver POSTs initialize at 2025-06-18 as hermes to a declared desktop app's loopback endpoint and reads only the HTTP status to decide whether the app is answering. Neither carries a session.

There is a genuine second ClientSession, in the computer-use backend. It spawns the cua-driver binary over stdio and talks to its MCP server, which makes Hermes an MCP client to a component it ships rather than to anything a user configures. That session, now in tools/computer_use/cua_backend_session.py, is constructed bare — no sampling callback, no elicitation callback, no client_info — and calls session.initialize() directly instead of going through _negotiate_session, so it declares no capabilities and has no server/discover fallback. It is not reachable from mcp_servers config and does not appear in the tool registry, so the registry entry describes the configurable path only.

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