browser_fill · Agent Browser MCP Server MCP: Risk & Policy

WHAT IT DOES

What browser_fill does on Agent Browser MCP Server

AI agents invoke browser_fill to trigger actions in Agent Browser MCP Server. 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_fill needs a policy

This tool fills form fields in a browser automation context, which constitutes executing a browser action. It can interact with login forms, payment forms, search fields, or any web form — making it potentially high severity as an AI agent could misuse it to submit credentials, personal data, or trigger sensitive web operations. The 'replacing existing values' aspect adds risk of overwriting important data.

From the tool's definition フォームフィールドに値を入力します（既存の値を置き換え）— fills form fields, replacing existing values; part of a browser automation suite that performs web interactions

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

browser_fill Rate-limited

browser_fill 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_fill": {
      "limits": [
        {
          "counter": "browser_fill_rate",
          "window": "minute",
          "max": 10,
          "scope": "grant"
        }
      ]
    }
  }
}

RATE-LIMIT THIS TOOL →

Instant setup, no code required.

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

FAQ

Questions about browser_fill

What does the browser_fill tool do? +

フォームフィールドに値を入力します（既存の値を置き換え）。. It is categorised as a Execute tool in the Agent Browser MCP Server 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_fill? +

Register the Agent Browser MCP Server MCP server in PolicyLayer and add a rule for browser_fill: 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 Agent Browser MCP Server. Nothing to install.

What risk level is browser_fill? +

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

Can I rate-limit browser_fill? +

Yes. Add a rate_limit block to the browser_fill 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_fill completely? +

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

browser_fill is provided by the Agent Browser MCP Server MCP server (nocall-corp/agent-browser-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.