browser_useragent_set

THE RISK

High Risk

Why browser_useragent_set needs a policy

This tool modifies browser behavior by overriding the JavaScript navigator.userAgent property and re-injecting it after each navigation. This is an Execute-class action because it runs JavaScript-side injection that actively manipulates the browser environment on an ongoing basis, affecting how web servers and scripts identify the client.

From the tool's definition Override navigator.userAgent (JS-side). Re-injected after navigation.

Documented attack patterns abuse exactly the kind of access browser_useragent_set gives an agent:

POLICY

How to control browser_useragent_set

PolicyLayer is an MCP gateway — it sits between your AI agents and Termux Browser Pilot, and nothing reaches the server without passing your rules. This is the rule we recommend for browser_useragent_set:

policy.json

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

browser_useragent_set 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.

Create a free account and register Termux Browser Pilot — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

RATE-LIMIT THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Termux Browser Pilot tools

Destructive browser_auth_delete Delete a saved auth session. Destructive browser_console_clear Clear all captured console log messages. Destructive browser_cookies_clear Clear all browser cookies. Destructive browser_dialog_clear Clear all captured dialog messages. Destructive browser_events_clear Clear all captured DOM events. Destructive browser_headers_clear Clear all custom HTTP headers and remove fetch/XHR hooks. Destructive browser_mock_clear Remove response mock(s). Destructive browser_mutations_clear Clear all captured DOM mutations.

All 148 Termux Browser Pilot tools →

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Go deeper

High-risk tools in Termux Browser Pilot → Every high-risk tool this server exposes, in one view.
All high-risk MCP tools → Every high-risk tool across the catalogue, and the policy pattern that contains them.
The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Agent sandbox → Bounding what an agent can execute and where the boundary should sit.
Least privilege for MCP → Granting agents the minimum tool surface the task needs.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about browser_useragent_set

What does the browser_useragent_set tool do? +

Override navigator.userAgent (JS-side). Re-injected after navigation. It is categorised as a Execute tool in the Termux Browser Pilot 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_useragent_set? +

Register the Termux Browser Pilot MCP server in PolicyLayer and add a rule for browser_useragent_set: 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 Termux Browser Pilot. Nothing to install.

What risk level is browser_useragent_set? +

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

Can I rate-limit browser_useragent_set? +

Yes. Add a rate_limit block to the browser_useragent_set 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_useragent_set completely? +

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

browser_useragent_set is provided by the Termux Browser Pilot MCP server (salviz/termux-browser-pilot). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Termux Browser Pilot tool call.

Start from Termux Browser Pilot, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →