browser_file_upload · Playwright MCP: Risk & Policy

WHAT IT DOES

What browser_file_upload does on Playwright MCP

AI agents use browser_file_upload 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_file_upload needs a policy

This tool enables an AI agent to programmatically upload files to web applications, which modifies state on remote systems. While uploads are typically reversible, the severity is high because an agent could upload malicious files, sensitive data to wrong destinations, or large quantities of unwanted files. The tool spans Write (file creation) but not Execute (no code running) or Destructive (uploads are undoable).

From the tool's definition Tool name 'browser_file_upload' and description 'Upload one or multiple files' indicate creation/modification of data on remote systems via browser automation. This is reversible (files can be deleted), distinguishing it from Destructive.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

browser_file_upload Rate-limited

browser_file_upload 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_file_upload": {
      "limits": [
        {
          "counter": "browser_file_upload_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 Playwright MCP, so you can run agents against it safely.

FAQ

Questions about browser_file_upload

What does the browser_file_upload tool do? +

Upload one or multiple files. 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_file_upload? +

Register the Playwright MCP server in PolicyLayer and add a rule for browser_file_upload: 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_file_upload? +

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

Can I rate-limit browser_file_upload? +

Yes. Add a rate_limit block to the browser_file_upload 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_file_upload completely? +

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

browser_file_upload is provided by the Playwright MCP server (markbustamante77/mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.