browser_assert_layout · MCP: Risk & Policy

WHAT IT DOES

What browser_assert_layout does on Mcp

AI agents invoke browser_assert_layout to trigger actions in 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 browser_assert_layout needs a policy

This tool executes JavaScript assertions in a browser context to validate element positioning and dimensions. While it doesn't modify data or trigger external operations directly, it executes evaluative code whose behavior depends on the target element argument. The 'Execute' category is appropriate because it involves running code logic (assertions) in a browser environment.

From the tool's definition Tool uses 'assert' operations on getBoundingClientRect() output, which evaluates DOM element layout properties. The 'Run' verb combined with assertion logic indicates code execution (JavaScript evaluation against browser DOM).

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

browser_assert_layout Rate-limited

browser_assert_layout 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": {
    "browser_assert_layout": {
      "limits": [
        {
          "counter": "browser_assert_layout_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 Mcp, so you can run agents against it safely.

FAQ

Questions about browser_assert_layout

What does the browser_assert_layout tool do? +

Run numeric layout assertions against getBoundingClientRect() for a target element. It is categorised as a Execute tool in the 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 browser_assert_layout? +

Register the MCP server in PolicyLayer and add a rule for browser_assert_layout: 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 Mcp. Nothing to install.

What risk level is browser_assert_layout? +

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

Can I rate-limit browser_assert_layout? +

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

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

browser_assert_layout is provided by the MCP server (victormyschik/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.