wait_for_signal · UI Bridge MCP: Risk & Policy

WHAT IT DOES

What wait_for_signal does on UI Bridge MCP

AI agents invoke wait_for_signal to trigger actions in UI Bridge MCP. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why wait_for_signal needs a policy

The tool appears designed to wait for or signal UI events/state changes, which constitutes triggering external operations. This is Execute-class (not Read, as it influences control flow; not Destructive, as effects are reversible; not Financial). Severity is medium due to potential for disrupting UI workflows or introducing delays.

From the tool's definition Tool name 'wait_for_signal' combined with server description stating it 'interact[s] with UI elements' and supports 'control mode for the runner's own UI' suggests triggering or awaiting external operations whose effects depend on context.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

wait_for_signal Rate-limited

wait_for_signal stays usable, but rate-capped — a runaway agent can't fire it dozens of times a minute. Everything else on the server is denied unless you say otherwise.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "wait_for_signal": {
      "limits": [
        {
          "counter": "wait_for_signal_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

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

FAQ

Questions about wait_for_signal

What does the wait_for_signal tool do? +

wait_for_signal. It is categorised as a Execute tool in the UI Bridge MCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on wait_for_signal? +

Register the UI Bridge MCP server in PolicyLayer and add a rule for wait_for_signal: 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 UI Bridge MCP. Nothing to install.

What risk level is wait_for_signal? +

wait_for_signal is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

Can I rate-limit wait_for_signal? +

Yes. Add a rate_limit block to the wait_for_signal 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 wait_for_signal completely? +

Set action: deny in the PolicyLayer policy for wait_for_signal. 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 wait_for_signal? +

wait_for_signal is provided by the UI Bridge MCP server (qontinui/ui-bridge-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.