ui_page_evaluate · UI Bridge MCP: Risk & Policy

WHAT IT DOES

What ui_page_evaluate does on UI Bridge MCP

AI agents invoke ui_page_evaluate 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 ui_page_evaluate needs a policy

The name 'ui_page_evaluate' strongly implies execution of code or expressions within a page context (analogous to Playwright/Puppeteer page.evaluate()), which would constitute arbitrary code execution in the UI. The description is empty, lowering confidence, but given the server's purpose of UI interaction and the naming convention, Execute is the most likely category.

From the tool's definition Tool name 'ui_page_evaluate' suggests evaluating/executing code or expressions in a UI page context, similar to browser page.evaluate() which runs JavaScript

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

ui_page_evaluate Rate-limited

ui_page_evaluate 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": {
    "ui_page_evaluate": {
      "limits": [
        {
          "counter": "ui_page_evaluate_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 ui_page_evaluate

What does the ui_page_evaluate tool do? +

ui_page_evaluate. 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 ui_page_evaluate? +

Register the UI Bridge MCP server in PolicyLayer and add a rule for ui_page_evaluate: 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 ui_page_evaluate? +

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

Can I rate-limit ui_page_evaluate? +

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

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

ui_page_evaluate 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.