debug_javascript_errors

THE RISK

Low Risk

Why debug_javascript_errors needs a policy

This tool queries and returns JavaScript error information from a running browser session. It performs passive introspection of errors that have already occurred, producing logs or stack traces for analysis. There are no arguments that would cause code execution, data modification, or external operations.

From the tool's definition Tool description states 'Get JavaScript errors' - a read operation that retrieves diagnostic data. The verb 'Get' and purpose 'identifying and debugging' indicate data retrieval with no side effects.

Documented attack patterns abuse exactly the kind of access debug_javascript_errors gives an agent:

POLICY

How to control debug_javascript_errors

PolicyLayer is an MCP gateway — it sits between your AI agents and Firefox MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for debug_javascript_errors:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "debug_javascript_errors": {}
  }
}

debug_javascript_errors is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.

Create a free account and register Firefox MCP Server — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

CAP THIS TOOL →

Free to start. No card required.

EXPLORE

Related tools and policies

More Firefox MCP Server tools

Destructive debug_buffers_clear Clear accumulated debug data buffers to free memory and start fresh monitoring. Destructive browser_close Close the entire browser instance and clean up all sessions and resources. Destructive session_close Close a specific browser session and clean up its resources. Execute browser_launch Launch Firefox browser with multi-session support and comprehensive debugging capabilities Execute debug_monitoring_start Start or restart comprehensive monitoring for console logs, errors, network activity, and Execute element_wait Wait for specific elements to appear or become visible. Essential for handling dynamic con Execute javascript_execute Execute custom JavaScript code in the browser context. Powerful for advanced DOM manipulat Execute page_navigate Navigate to a specific URL in the browser. Works with any web page or web application.

All 29 Firefox MCP Server tools →

Read tools on other servers

M-Team MCP Server get_torrent_detail YouTube MCP Server search_channel Android Forensics ADB MCP Server parse_browser_history 0xarchive web3_challenge

Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Data exfiltration → How read access becomes an exfiltration channel when chained with untrusted content.
MCP token cost → What connecting this server costs in context-window tokens on every request.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about debug_javascript_errors

What does the debug_javascript_errors tool do? +

Get JavaScript errors and exceptions with full stack traces. Critical for identifying and debugging client-side issues. It is categorised as a Read tool in the Firefox MCP Server MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on debug_javascript_errors? +

Register the Firefox MCP Server MCP server in PolicyLayer and add a rule for debug_javascript_errors: 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 Firefox MCP Server. Nothing to install.

What risk level is debug_javascript_errors? +

debug_javascript_errors is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit debug_javascript_errors? +

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

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

debug_javascript_errors is provided by the Firefox MCP Server MCP server (jediluke/firefox-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every Firefox MCP Server tool call.

Start from Firefox MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →