Get all CSS custom properties (--*) defined in the page with their values
AI agents call get_css_variables 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.
This tool only reads and queries styling metadata from the DOM without modifying any state, executing code, or producing side effects. It is purely informational, similar to other read-only tools on the server like 'describe_ui' and 'get_computed_styles'. The low severity reflects minimal risk even if misused by an agent, as accessing CSS variables poses no security or operational threat.
From the tool's definition Tool retrieves CSS custom properties (--*) defined in a page with their values. The description indicates a retrieval operation with 'Get all CSS custom properties...with their values' - no creation, modification, execution, or deletion of data.
Attacks that exploit this kind of access
Get all CSS custom properties (--*) defined in the page with their values. 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 get_css_variables: 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.
get_css_variables 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 get_css_variables 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 get_css_variables. 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.
get_css_variables 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.
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