fill · Opera DevTools MCP: Risk & Policy

WHAT IT DOES

What fill does on Opera DevTools MCP

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

WHY IT NEEDS A POLICY

Why fill needs a policy

The tool creates or modifies data (form field contents) reversibly. While it affects browser state, the modifications can be undone (cleared, reset, or overwritten). This is distinct from Execute because it doesn't run arbitrary code or trigger external operations—it only populates form fields. It's not Destructive because changes are reversible.

From the tool's definition Tool description states "Type text into an input, text area or select an option from a <select> element." This modifies input field values and form data, which are reversible state changes on a web page.

Attacks that exploit this kind of access

Recommended rule Ready

Verdict

fill Rate-limited

fill 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": {
    "fill": {
      "limits": [
        {
          "counter": "fill_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 Opera DevTools MCP, so you can run agents against it safely.

FAQ

Questions about fill

What does the fill tool do? +

Type text into an input, text area or select an option from a <select> element. It is categorised as a Write tool in the Opera DevTools 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 fill? +

Register the Opera DevTools MCP server in PolicyLayer and add a rule for 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 Opera DevTools MCP. Nothing to install.

What risk level is fill? +

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

Can I rate-limit fill? +

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

Set action: deny in the PolicyLayer policy for 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 fill? +

fill is provided by the Opera DevTools MCP server (operasoftware/opera-devtools-mcp). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.