add_cookie · Mcp Selenium MCP: Risk & Policy

WHAT IT DOES

What add_cookie does on Mcp Selenium

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

WHY IT NEEDS A POLICY

Why add_cookie needs a policy

Adding a cookie modifies browser session data reversibly. While this could potentially be misused to set tracking cookies or malicious session tokens, it does not execute arbitrary code, delete data, move money, or cause irreversible harm. It falls squarely in the Write category (creates/modifies data reversibly).

From the tool's definition Tool name 'add_cookie' and description 'adds a cookie to the current browser session' clearly indicate modification of browser state data. This is a write operation that creates or modifies cookies.

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"
        }
      ]
    }
  }
}

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 Selenium, so you can run agents against it safely.

FAQ

Questions about add_cookie

What does the add_cookie tool do? +

adds a cookie to the current browser session. The browser must be on a page from the cookie. It is categorised as a Write tool in the Mcp 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 Mcp 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 Mcp 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 Mcp Selenium MCP server (@angiejones/mcp-selenium). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.