AI agents call browser_localstorage_list to retrieve information from Playwright without modifying anything — typically the context-gathering step in research, monitoring, and reporting workflows, before the agent takes action elsewhere.
This tool retrieves local storage data from a browser context, which is a read-only query operation. However, severity is medium rather than low because local storage may contain sensitive authentication tokens, session data, or PII that could be exposed to an AI agent. No destructive or financial impact, but data sensitivity elevation justifies medium over low.
From the tool's definition Tool name 'browser_localstorage_list' indicates listing/querying browser local storage. Sibling tools like 'browser_cookie_list', 'browser_cookie_get' are clearly Read operations. The '_list' suffix suggests retrieval without modification.
Documented attack patterns abuse exactly the kind of access browser_localstorage_list gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and Playwright, and nothing reaches the server without passing your rules. This is the rule we recommend for browser_localstorage_list:
{
"version": "1",
"default": "deny",
"tools": {
"browser_localstorage_list": {}
}
}browser_localstorage_list is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.
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browser_localstorage_list. It is categorised as a Read tool in the Playwright MCP Server, which means it retrieves data without modifying state.
Register the Playwright MCP server in PolicyLayer and add a rule for browser_localstorage_list: 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. Nothing to install.
browser_localstorage_list 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 browser_localstorage_list 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 browser_localstorage_list. 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.
browser_localstorage_list is provided by the Playwright MCP server (@playwright/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from Playwright, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
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68 Playwright tools catalogued and risk-classified — across an index of 43,000+ MCP servers.