browser_file_upload · Playwright MCP: Risk & Policy

WHAT IT DOES

What browser_file_upload does on Playwright MCP

AI agents invoke browser_file_upload to trigger actions in Playwright MCP. What it does depends on the arguments the agent supplies, and its effects often reach beyond the immediate call — builds kicked off, notifications sent, workflows started.

WHY IT NEEDS A POLICY

Why browser_file_upload needs a policy

File upload is an external operation that sends data to remote systems. The actual impact depends on what files are uploaded and where; it can cause irreversible side effects on external services (e.g., publishing content, submitting forms with documents). It spans Write/Execute territory, but since it executes a browser action interacting with external systems, Execute is most appropriate.

From the tool's definition 'Upload one or multiple files' — triggers an external browser file upload operation whose effects depend on the target site and files uploaded

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

browser_file_upload Rate-limited

browser_file_upload stays usable, but rate-capped — a runaway agent can't fire it dozens of times 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": 10,
          "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 Execute tool in the Playwright MCP MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

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 Execute tool with high risk. Execute tools should be rate-limited and have argument validation enabled.

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 (nzjami/mcpplaywright). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.