AI agents use user_agent to create or update resources in OpenChrome — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your OpenChrome environment.
This tool modifies the browser's user agent string, which is a reversible configuration change. It doesn't read data, execute code, or delete anything, but it does alter browser state that can affect how websites identify and interact with the automated browser. Misuse could enable deceptive browsing behavior (e.g., spoofing a different browser/OS), hence medium severity.
From the tool's definition Set or reset browser user agent
Documented attack patterns abuse exactly the kind of access user_agent gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and OpenChrome, and nothing reaches the server without passing your rules. This is the rule we recommend for user_agent:
{
"version": "1",
"default": "deny",
"tools": {
"user_agent": {
"limits": [
{
"counter": "user_agent_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}user_agent stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
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Set or reset browser user agent. It is categorised as a Write tool in the OpenChrome MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the OpenChrome MCP server in PolicyLayer and add a rule for 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 OpenChrome. Nothing to install.
user_agent is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the 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 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.
user_agent is provided by the OpenChrome MCP server (shaun0927/openchrome). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Deterministic rules across all 106 OpenChrome tools. Per-identity grants. Full audit log. Live in minutes. Nothing to install.
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106 OpenChrome tools catalogued and risk-classified — across an index of 42,500+ MCP servers.