browser_set_storage_state · Playwright MCP: Risk & Policy

WHAT IT DOES

What browser_set_storage_state does on Playwright MCP

AI agents use browser_set_storage_state to create or update resources in Playwright MCP — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your Playwright MCP environment.

WHY IT NEEDS A POLICY

Why browser_set_storage_state needs a policy

This tool creates or modifies persistent browser storage state, which is a reversible write operation. It does not execute arbitrary code (Execute), delete data (Destructive), or move money (Financial). However, the severity is high because an agent could use it to inject malicious session tokens, authentication credentials, or tracking data that affects subsequent page interactions or compromises user sessions.

From the tool's definition Tool name 'browser_set_storage_state' indicates modification of browser storage (localStorage, sessionStorage, or similar). The verb 'set' explicitly denotes a write operation.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

browser_set_storage_state Rate-limited

browser_set_storage_state 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.

View as policy code

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "browser_set_storage_state": {
      "limits": [
        {
          "counter": "browser_set_storage_state_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

LIMIT THIS TOOL →

Instant setup, no code required.

PolicyLayer is an MCP gateway: every tool call is checked against your rule before it reaches Playwright MCP, so you can run agents against it safely.

FAQ

Questions about browser_set_storage_state

What does the browser_set_storage_state tool do? +

browser_set_storage_state. It is categorised as a Write tool in the Playwright MCP MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on browser_set_storage_state? +

Register the Playwright MCP server in PolicyLayer and add a rule for browser_set_storage_state: 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. Nothing to install.

What risk level is browser_set_storage_state? +

browser_set_storage_state is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.

Can I rate-limit browser_set_storage_state? +

Yes. Add a rate_limit block to the browser_set_storage_state 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.

How do I block browser_set_storage_state completely? +

Set action: deny in the PolicyLayer policy for browser_set_storage_state. 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.

What MCP server provides browser_set_storage_state? +

browser_set_storage_state is provided by the Playwright MCP server (roshan571/playwright-mcp2). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.