files.write_text · MCP Playwright Browser MCP: Risk & Policy

WHAT IT DOES

What files.write_text does on MCP Playwright Browser

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

WHY IT NEEDS A POLICY

Why files.write_text needs a policy

This tool creates or modifies files on the system where the MCP server runs. While reversible (files can be edited or deleted), the 'arbitrary' nature means an AI agent could write malicious content to sensitive locations (configuration files, scripts, credentials) or overwrite important data.

From the tool's definition Tool name 'files.write_text' combined with description 'Write arbitrary text to a file path' explicitly indicates file creation or modification capability.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

files.write_text Rate-limited

files.write_text 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": {
    "files.write_text": {
      "limits": [
        {
          "counter": "files.write_text_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 Browser, so you can run agents against it safely.

FAQ

Questions about files.write_text

What does the files.write_text tool do? +

Write arbitrary text to a file path. It is categorised as a Write tool in the MCP Playwright Browser MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.

How do I enforce a policy on files.write_text? +

Register the MCP Playwright Browser MCP server in PolicyLayer and add a rule for files.write_text: 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 Browser. Nothing to install.

What risk level is files.write_text? +

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

Can I rate-limit files.write_text? +

Yes. Add a rate_limit block to the files.write_text 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 files.write_text completely? +

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

files.write_text is provided by the MCP Playwright Browser MCP server (mhrnqaruni/mcp-playwright-browser). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.