Install models and tools

The ptc-host.json installs credentials, model routes, MCP tools, and limits. An application selects and narrows aliases without changing host configuration.

How do I install a model?

Install one model alias with a credential read from the process environment:

{
  "credentials": {
    "model_key": {"env": "OPENROUTER_API_KEY"}
  },
  "install": {
    "model": {
      "source": "llm",
      "structured_output_mode": "unsupported",
      "usage_guarantees": {"tokens": true, "cost_currency": "USD"},
      "installation_revision": "model-v1",
      "model": "openrouter:deepseek/deepseek-v4-flash",
      "credential": "model_key",
      "params": {"max_tokens": 4096}
    }
  }
}

Keep its path in ptc-project.json, then verify the selected application:

ptc doctor ptc-project.json
ptc doctor ptc-project.json --connect
ptc models ptc-project.json

Plain doctor validates configuration without loading credentials or dialing providers. --connect is a connectivity probe and may consume resources.

See usage guarantees for the required accounting policy.

How do I install an MCP server?

Install MCP tools with the same separation: the host fixes the transport and public tool mapping, while the application selects the alias and may narrow a write-bearing tool set. The workspace alias selected in Configure an application is installed as a second entry under the same install object:

{
  "workspace": {
    "source": "mcp",
    "installation_revision": "workspace-v1",
    "transport": {
      "type": "stdio",
      "command": "node",
      "args": ["server.js"]
    },
    "tools": {
      "read_text_file": {"as": "workspace.read", "effect": "read"}
    },
    "ceilings": {"timeout_ms": 15000, "max_result_bytes": 262144}
  }
}

The upstream operation name and server command belong to the server you run. You choose the public as name and its read or write effect. Follow Connect an MCP tool for one complete workflow against a checked-in server.

ptc validate reports installation_config_digests for the selected aliases so you can compare the host declaration you reviewed with the one a later validation or run actually named. The digest is configuration identity, not proof of live server scope; see the host-configuration reference.

Where is the complete contract?

The host-configuration reference owns the complete credential forms, provider sources, transport rules, OAuth behavior, data classes, ceilings, and diagnostics.