add_cookie · Selenium MCP: Risk & Policy

WHAT IT DOES

What add_cookie does on Selenium

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

WHY IT NEEDS A POLICY

Why add_cookie needs a policy

Adding cookies is a reversible Write operation that modifies browser state. While it could facilitate security attacks (e.g., session hijacking if combined with domain-level access), the operation itself is not destructive and can be undone by deleting the cookie.

From the tool's definition Tool name 'add_cookie' and description 'Add a cookie' indicates the tool creates or modifies cookie data in the browser. Cookies are persistent client-side data that persist across browser sessions.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

add_cookie Rate-limited

add_cookie 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": {
    "add_cookie": {
      "limits": [
        {
          "counter": "add_cookie_rate",
          "window": "minute",
          "max": 30,
          "scope": "grant"
        }
      ]
    }
  }
}

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

FAQ

Questions about add_cookie

What does the add_cookie tool do? +

Add a cookie. Browser must be on a page from the cookie's domain. It is categorised as a Write tool in the Selenium MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on add_cookie? +

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

What risk level is add_cookie? +

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

Can I rate-limit add_cookie? +

Yes. Add a rate_limit block to the add_cookie 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 add_cookie completely? +

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

add_cookie is provided by the Selenium MCP server (scv-consultants/selenium-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.