fill_web_form · Nexus Core MCP: Risk & Policy

WHAT IT DOES

What fill_web_form does on Nexus Core

AI agents invoke fill_web_form to trigger actions in Nexus Core. 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 fill_web_form needs a policy

This tool performs browser automation - navigating to URLs and filling web forms with simulated human input. This constitutes executing external operations (browser actions) that can trigger submissions, logins, signups, purchases, or other web interactions. The APPROVAL-GATED label confirms the system recognizes its elevated risk.

From the tool's definition navigate to URL, fill named fields with human-like typing

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

fill_web_form Rate-limited

fill_web_form 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": {
    "fill_web_form": {
      "limits": [
        {
          "counter": "fill_web_form_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 Nexus Core, so you can run agents against it safely.

FAQ

Questions about fill_web_form

What does the fill_web_form tool do? +

APPROVAL-GATED: navigate to URL, fill named fields with human-like typing. It is categorised as a Execute tool in the Nexus Core MCP Server, which means it can trigger actions or run processes. Use rate limits and argument validation.

How do I enforce a policy on fill_web_form? +

Register the Nexus Core MCP server in PolicyLayer and add a rule for fill_web_form: 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 Nexus Core. Nothing to install.

What risk level is fill_web_form? +

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

Can I rate-limit fill_web_form? +

Yes. Add a rate_limit block to the fill_web_form 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 fill_web_form completely? +

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

fill_web_form is provided by the Nexus Core MCP server (noumenon-ai/nexus-core). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.