cookies_set · MCP Playwright Server MCP: Risk & Policy

WHAT IT DOES

What cookies_set does on MCP Playwright Server

AI agents use cookies_set 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 cookies_set needs a policy

This tool creates or modifies cookies in the browser context, which is a reversible write operation. While cookies can be deleted, the tool itself performs creation/modification (Write category). Severity is high because misuse could set malicious authentication tokens, hijack sessions, or inject tracking/exploit cookies that affect subsequent browser behavior and could compromise user security or application state.

From the tool's definition 'Add one or more cookies to the browser context' - directly modifies browser state by writing cookies. Description explicitly mentions 'setting authentication tokens or session data', which are security-sensitive operations.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

cookies_set Rate-limited

cookies_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": {
    "cookies_set": {
      "limits": [
        {
          "counter": "cookies_set_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 cookies_set

What does the cookies_set tool do? +

Add one or more cookies to the browser context. Useful for setting authentication tokens or session data. 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 cookies_set? +

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

What risk level is cookies_set? +

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

Can I rate-limit cookies_set? +

Yes. Add a rate_limit block to the cookies_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 cookies_set completely? +

Set action: deny in the PolicyLayer policy for cookies_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 cookies_set? +

cookies_set 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.