gc_mcp

gc_mcp exposes Grand Central daemon capabilities as MCP tools.

It is a client, not a server of record: every tool call is proxied to a running gc_daemon. Without one listening on GC_DAEMON_URL (default http://localhost:4242) the tools will load and then fail to reach anything.

Install

Point your MCP client at it — no clone or build required:

{
  "mcpServers": {
    "gc": {
      "command": "npx",
      "args": ["-y", "@fosferon/gc-mcp"]
    }
  }
}

Or install it and use the binary directly:

npm install -g @fosferon/gc-mcp
gc-mcp                     # stdio (default) — the binary is unscoped
GC_MCP_TRANSPORT=streamable-http gc-mcp

From a clone, npm install && npm run build then point the client at node /path/to/gc_mcp/dist/index.js.

Parameter validation

Every tool rejects unsupported top-level parameters before its callback can contact gc_daemon. MCP returns its standard isError: true tool result; the diagnostic names the rejected parameter and lists the parameters registered for that tool. This makes a misspelled or obsolete option recoverable instead of silently ignoring it.

This boundary does not alter nested payload contracts: a declared map or object parameter continues to accept the nested values its existing schema allows.

Configuration

Variable	Default	Purpose
GC_DAEMON_URL	http://localhost:4242	Base URL of the gc_daemon this wraps.
GC_MCP_TRANSPORT	stdio	stdio, streamable-http, or all.
GC_MCP_HOST	127.0.0.1	Bind host, streamable-http only.
GC_MCP_PORT	8765	Bind port, streamable-http only.
GC_MCP_PATH	/mcp	HTTP path, streamable-http only.
GH_TOKEN	—	GitHub token for the gh_* tools. Falls back to ~/.config/gh-token.
GH_DEFAULT_REPO	unset	owner/repo used by the read-only gh_* tools when repo is omitted.

Why GH_DEFAULT_REPO does not apply to writes

gh_issue_create, gh_issue_edit and gh_issue_comment require an explicit repo. A write that infers its target from ambient configuration will eventually file into the wrong tracker, and the caller who omitted the argument gets no signal that it happened — the operation succeeds, somewhere else. Reads carry no such consequence, so they may fall back to the environment.

There is deliberately no compiled-in default. A shipped repository name aims every installation's bare calls at whatever tracker the author last worked on.