save_storage_state · MCP Playwright Server MCP

WHAT IT DOES

What save_storage_state does on MCP Playwright Server

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

WHY IT NEEDS A POLICY

Why save_storage_state needs a policy

This tool creates and stores authentication artifacts (cookies, localStorage) that persist state. While not destructive, it modifies the browser's stored state in a way that could be misused to exfiltrate or persist unauthorized sessions, capture credentials, or enable replay attacks. The 'save' operation is reversible (storage can be cleared), making it Write rather than Destructive.

From the tool's definition Tool name is 'save_storage_state' and description states it 'Save[s] browser storage state (cookies, localStorage)'. This explicitly involves creating or persisting authentication credentials and session data.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

save_storage_state Rate-limited

save_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": {
    "save_storage_state": {
      "limits": [
        {
          "counter": "save_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 MCP Playwright Server, so you can run agents against it safely.

FAQ

Questions about save_storage_state

What does the save_storage_state tool do? +

Save browser storage state (cookies, localStorage) for authentication reuse. It is categorised as a Write tool in the MCP Playwright Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on save_storage_state? +

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

What risk level is save_storage_state? +

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

Can I rate-limit save_storage_state? +

Yes. Add a rate_limit block to the save_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 save_storage_state completely? +

Set action: deny in the PolicyLayer policy for save_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 save_storage_state? +

save_storage_state is provided by the MCP Playwright Server MCP server (j0hanz/playwright-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.