Set a custom User Agent for the browser
AI agents invoke playwright_custom_user_agent to trigger actions in Playwright MCP Server. 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.
Setting a custom User Agent changes the browser's runtime configuration, which can affect all subsequent web interactions. It's not a simple read, and while it modifies state, it operates at the browser execution environment level rather than creating/updating persistent data.
From the tool's definition 'Set a custom User Agent for the browser' — modifies browser configuration/state, affecting how the browser identifies itself to external servers
Documented attack patterns abuse exactly the kind of access playwright_custom_user_agent gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Playwright MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for playwright_custom_user_agent:
{
"version": "1",
"default": "deny",
"tools": {
"playwright_custom_user_agent": {
"limits": [
{
"counter": "playwright_custom_user_agent_rate",
"window": "minute",
"max": 10,
"scope": "grant"
}
]
}
}
}playwright_custom_user_agent 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.
Free to start. No card required.
Set a custom User Agent for the browser. It is categorised as a Execute tool in the Playwright MCP Server MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.
Register the Playwright MCP Server MCP server in PolicyLayer and add a rule for playwright_custom_user_agent: 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 Playwright MCP Server. Nothing to install.
playwright_custom_user_agent 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 playwright_custom_user_agent 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 playwright_custom_user_agent. 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.
playwright_custom_user_agent is provided by the Playwright MCP Server MCP server (pvinis/mcp-playwright-stealth). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Playwright MCP Server, 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.
29 Playwright MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.