Policy Files¶

--policies-json accepts either inline JSON or a path to a JSON file. The CLI help documents the first-pass shape as:

{
  "fetch": {
    "mode": "all",
    "policies": [
      {
        "url": "file:///abs/path/fetch.rego",
        "policy_path": "mcp/fetch",
        "rule": "data.mcp.fetch.allow"
      }
    ]
  },
  "modules": {
    "mode": "all",
    "policies": []
  }
}

Useful keys:

• top-level operation keys: fetch, modules, filesystem, mcp_tools, and subprocess
• per-operation keys: mode and policies
• mode: "all" or "any"; omitted means "all"
• policies: ordered list of policy sources
• per-policy keys:
• url: required; http:// and https:// point at remote OPA, file:// points at a local .rego file or directory
• policy_path: optional remote OPA data path
• rule: optional local Regorus rule path

For local fetch policies, omitting rule uses the default data.mcp.fetch.allow.

Minimal local Rego from server/tests/local_opa_policy.rs:

package mcp.fetch
default allow = false

allow if {
    input.method == "GET"
}

That test is wired with a policy entry like {"url":"file:///.../fetch.rego","policy_path":null,"rule":null}, which is enough for fetch gating because the default fetch rule path is applied.

For the behavior model behind these configuration keys, see Policy System, Network Access, and Filesystem Access.