Use ptc-host.json to install credentials, model routes, MCP tools, and outer
limits separately from an application.
ptc.json may select an installed alias
and ask for less, but it cannot create one or change its credentials, endpoint,
command, effects, or ceilings.
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",
"installation_revision": "model-v1",
"model": "openrouter:deepseek/deepseek-v4-flash",
"credential": "model_key",
"cache": false,
"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 an explicit connectivity probe and may consume remote
resources.
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.