switch_runner · Yaver MCP: Risk & Policy

WHAT IT DOES

What switch_runner does on Yaver

AI agents use switch_runner to create or update resources in Yaver — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Yaver environment.

PARAMETERS

Parameter	Type	Required	Description
`runner_id`	string	Yes	Runner ID — claude, codex, or opencode.

Parameters from the server's own tool schema.

WHY IT NEEDS A POLICY

Why switch_runner needs a policy

An AI agent can call switch_runner faster than any human can review — one bad instruction and it creates or modifies resources in Yaver by the hundred, each call as confident as the last.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

switch_runner Rate-limited

switch_runner stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "switch_runner": {
      "limits": [
        {
          "counter": "switch_runner_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Yaver, so you can run agents against it safely.

FAQ

Questions about switch_runner

What does the switch_runner tool do? +

Switch the active AI runner. Available: claude, codex, aider. It is categorised as a Write tool in the Yaver MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

What parameters does switch_runner accept? +

switch_runner accepts 1 parameter: runner_id. Required: runner_id. The full parameter table on this page comes from the server's own tool schema.

How do I enforce a policy on switch_runner? +

Register the Yaver MCP server in PolicyLayer and add a rule for switch_runner: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches Yaver. Nothing to install.

What risk level is switch_runner? +

switch_runner is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit switch_runner? +

Yes. Add a rate_limit block to the switch_runner rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block switch_runner completely? +

Set action: deny in the PolicyLayer policy for switch_runner. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides switch_runner? +

switch_runner is provided by the Yaver MCP server (yaver-cli). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.