Execute JavaScript in a Chrome/Electron tab. Returns the result. WARNING: This runs arbitrary JS in the browser context — avoid on sensitive pages (banking, email). All executions are audit-logged.
AI agents invoke browser_js to trigger actions in ScreenHand. 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.
This tool executes arbitrary code (JavaScript) in a browser context, which is the definition of Execute category. While the execution itself is not destructive or financial by default, it can trigger external operations, modify DOM state, exfiltrate data, or interact with web services depending on the JS payload.
From the tool's definition Tool description explicitly states 'Execute JavaScript in a Chrome/Electron tab' and 'runs arbitrary JS in the browser context'.
Documented attack patterns abuse exactly the kind of access browser_js gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and ScreenHand, and nothing reaches the server without passing your rules. This is the rule we recommend for browser_js:
{
"version": "1",
"default": "deny",
"tools": {
"browser_js": {
"limits": [
{
"counter": "browser_js_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}browser_js 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.
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Execute JavaScript in a Chrome/Electron tab. Returns the result. WARNING: This runs arbitrary JS in the browser context — avoid on sensitive pages (banking, email). All executions are audit-logged. It is categorised as a Execute tool in the ScreenHand MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the ScreenHand MCP server in PolicyLayer and add a rule for browser_js: 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 ScreenHand. Nothing to install.
browser_js is a Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.
Yes. Add a rate_limit block to the browser_js 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.
Set action: deny in the PolicyLayer policy for browser_js. 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.
browser_js is provided by the ScreenHand MCP server (manushi4/screenhand). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from ScreenHand, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
89 ScreenHand tools catalogued and risk-classified — across an index of 43,000+ MCP servers.