browser_cookie_set · Playwright MCP: Risk & Policy

WHAT IT DOES

What browser_cookie_set does on Playwright MCP

AI agents use browser_cookie_set 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_cookie_set needs a policy

Setting cookies modifies browser session state but does not irreversibly delete data (Destructive), execute arbitrary code (Execute), or move money (Financial). This is a Write operation. Severity is high because an AI agent could maliciously set authentication cookies, session tokens, or tracking cookies to impersonate users, escalate privileges, or exfiltrate data.

From the tool's definition Tool name 'browser_cookie_set' indicates it sets (creates or modifies) cookies. Sibling tools include 'browser_cookie_delete' and 'browser_cookie_clear', confirming this server manages cookie state.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

browser_cookie_set Rate-limited

browser_cookie_set 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_cookie_set": {
      "limits": [
        {
          "counter": "browser_cookie_set_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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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_cookie_set

What does the browser_cookie_set tool do? +

browser_cookie_set. 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_cookie_set? +

Register the Playwright MCP server in PolicyLayer and add a rule for browser_cookie_set: 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_cookie_set? +

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

Can I rate-limit browser_cookie_set? +

Yes. Add a rate_limit block to the browser_cookie_set 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_cookie_set completely? +

Set action: deny in the PolicyLayer policy for browser_cookie_set. 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_cookie_set? +

browser_cookie_set is provided by the Playwright MCP server (naumana3services-maker/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.