Search the DOM tree for elements matching a tag name, class, or ID
AI agents call query_selector to retrieve information from Mcp Browser Lens without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
The tool performs DOM querying to locate elements based on selectors. It retrieves data about the page structure with no side effects, no data modification, no code execution, and no irreversible actions. This is a standard Read operation consistent with browser inspection APIs. The low severity reflects minimal risk even if misused—an agent querying the DOM cannot cause harm beyond information disclosure.
From the tool's definition Tool name 'query_selector' and description 'Search the DOM tree for elements matching a tag name, class, or ID' indicate a read-only operation that retrieves DOM information without modifying or executing code.
Attacks that exploit this kind of access
Search the DOM tree for elements matching a tag name, class, or ID. It is categorised as a Read tool in the Mcp Browser Lens MCP Server, which means it retrieves data without modifying state.
Register the Mcp Browser Lens MCP server in PolicyLayer and add a rule for query_selector: 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 Mcp Browser Lens. Nothing to install.
query_selector is a Read tool with low risk. Read-only tools are generally safe to allow by default.
Yes. Add a rate_limit block to the query_selector 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 query_selector. 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.
query_selector is provided by the Mcp Browser Lens MCP server (nano-step/mcp-browser-lens). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Every MCP server has a record like this.
Type a name, get the same breakdown: verified identity, auth posture, risk grade, capabilities, recommended policy.
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