MCP export

For a host that can only add an MCP server, the reference export is one tool named hcp that wraps the CLI, instead of one tool per command. Search, install, Skill, availability and exec all go through it, so the host takes new packs without a config change, which a host given one tool per command never could. Run hcpx adopt mcp --write and point the host at hcpx mcp.

How a call runs#

The tool's argument is the same argv you would type after hcpx. The server is no shell, so it rejects pipes, substitution and chaining, and it runs each call inside its own process the way hcpx runs it in a terminal: one runtime load and no new CLI process. Every call still goes through Policy, Binding and the sandbox, and the access commands refuse the agent there as they do in its shell.

Host (MCP only)
   │  tools/list → [hcp]
   │  tools/call { args: "exec transit plan -- from=A to=B" }
   ▼
hcpx mcp  (stdio)  →  run that argv in this process  (no shell, no new process)
   ▼
exec transit plan --json -- from=A to=B
   ▼
runtime (§6.3)  →  spawns the pack's CLI

Run it#

Terminal

bun add -g @harnesscontextprotocol/cli   # GitHub Packages preview: /docs/quickstart#install-the-cli
hcpx adopt mcp --write
hcpx mcp                                  # stdio server

Adopt writes .hcp/mcp.json:

JSON

{
  "mcpServers": {
    "hcp": {
      "command": "hcpx",
      "args": ["mcp"],
      "env": { "HCP_HOME": "~/.hcp" }
    }
  }
}

command is the name that starts the CLI on your machine. Point the host at that command, then call the one tool named hcp:

`args` (string)	`argv` (array)	What happens
`search transit`	`["search","transit"]`	Catalog search
`skill transit`	`["skill","transit"]`	Skill text
`availability transit`	`["availability","transit"]`	Four-flag availability
`exec transit plan -- from=A to=B`	`["exec","transit","plan","--","from=A","to=B"]`	Execute through the runtime
`install npm:@scope/pack`	`["install","npm:@scope/pack"]`	Install a pack package

Prefer argv when the host can pass an array, and use args, the bash-like form, when it only sends a string. Neither is a shell, and both reject metacharacters.

For reading, resources/list exposes hcp://catalog, hcp://help and hcp://skill/<pack_id> for installed packs, with no extra tools. Actions still go through the single hcp tool, and writes still need confirm=true when Policy says so, so MCP gives the model no way around the gate.

What the export does not do#

Installing the MCP server installs no pack, because hcpx install still copies the three files. When the host can load HCP directly, native adopt (coding agents) is the better path, for the reasons in Adopt in a host. The normative rules are in §12.5.

How a call runs#

Run it#

What the export does not do#

Related#