crow_browser_evaluate

Execute JavaScript in the page context and return the result.

SERVERCrow SOURCEkh0pper/crow

High RISK CLASS

Category Execute

Parameters 00 required

Recommended Rate-limitedsee the rule below

Registry record Grade F, identity unverified Pull the record →

This record as markdown: /tools/kh0pper-crow/crow-browser-evaluate.md

WHAT IT DOES

What crow_browser_evaluate does on Crow

AI agents invoke crow_browser_evaluate to trigger actions in Crow. 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.

RISK

Why crow_browser_evaluate is rated High

This tool allows execution of JavaScript code, which is a form of code execution. While the blast radius is somewhat bounded to the browser context (unlike shell execution), JavaScript can still perform significant side effects including DOM manipulation, data exfiltration, form submission, credential theft, and interaction with web services.

From the tool's definition Tool name 'crow_browser_evaluate' combined with description 'Execute JavaScript in the page context and return the result' explicitly indicates execution of arbitrary code within a browser environment.

Attacks that exploit this kind of access

RECOMMENDED RULE

The rule that runs crow_browser_evaluate safely

PolicyLayer is an MCP gateway: it sits between your AI agents and Crow, and checks every tool call against a rule you set before the call runs. Nothing changes on the server itself. For crow_browser_evaluate, this is the rule to start with:

crow_browser_evaluate Rate-limited

crow_browser_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": {
    "crow_browser_evaluate": {
      "limits": [
        {
          "counter": "crow_browser_evaluate_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL → Instant setup, no code required.

The button opens the PolicyLayer dashboard: create your workspace, connect Crow, apply this rule, and every crow_browser_evaluate call is checked against it from then on.

FAQ

Questions about crow_browser_evaluate

What does the crow_browser_evaluate tool do? +

Execute JavaScript in the page context and return the result. It is categorised as a Execute tool in the Crow MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on crow_browser_evaluate? +

Register the Crow MCP server in PolicyLayer and add a rule for crow_browser_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 Crow. Nothing to install.

What risk level is crow_browser_evaluate? +

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

Can I rate-limit crow_browser_evaluate? +

Yes. Add a rate_limit block to the crow_browser_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 crow_browser_evaluate completely? +

Set action: deny in the PolicyLayer policy for crow_browser_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 crow_browser_evaluate? +

crow_browser_evaluate is provided by the Crow MCP server (kh0pper/crow). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

KEEP EXPLORING

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