troubleshooting

A troubleshooting guide for Chrome DevTools MCP, a connection that lets an agent work with a browser's developer tools. It diagnoses problems with listing pages, opening pages, navigating, or starting the server.

In plain words
What is it for?
It is for checking MCP configuration files, reviewing launch options and environment variables, and resolving browser developer-tools connection failures.
Why use it?
It gives a structured way to find configuration mistakes and common connection errors instead of guessing at fixes.

Skill for Claude CodeCodex

Part of the opera-devtools-mcp plugin — 6 skills, 1 MCP server shipped together

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/operasoftware/opera-devtools-mcp/troubleshooting
Any agent
npx skills add operasoftware/opera-devtools-mcp --skill troubleshooting
Clone the repo
git clone --depth 1 https://github.com/operasoftware/opera-devtools-mcp

Made for: Claude Code, Codex.

Or install opera-devtools-mcp, the plugin that ships this one along with the rest of its 6 skills, 1 MCP server.

Per session 40 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 1,519 The whole file, excluding the scripts and references it only reads on demand.
Security scan B 1 finding. Scan, not verified.
Origin 100% copy Near-identical to another mod in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00040 $0.01519
Opus 5 $0.00020 $0.00759
Sonnet 5 $0.00008 $0.00304
Haiku 4.5 $0.00004 $0.00152

Measured 3d ago against content hash f7deca2af0ea, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade B, and why

troubleshooting scanned grade B with 1 finding against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 3d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Reads MCP configurationmediumAgent snooping

mcp.json carries server URLs and auth tokens; reading it lets a mod discover and abuse other integrations.

Your first action should be to locate and read the MCP configuration file. Search for the following files in the user's workspace: `.mcp.json`, `gemini-extension.json`, `.claude/settings.json`, `.vscode/launch.json`, or
Origin

This is a copy

100% identical to troubleshooting — 1 line differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

skills/troubleshooting/SKILL.md · 99 lines

How it starts

The opening of the file, as written. The whole thing — 99 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Troubleshooting Wizard

You are acting as a troubleshooting wizard to help the user configure and fix their Chrome DevTools MCP server setup. When this skill is triggered (e.g., because list_pages, new_page, or navigate_page failed, or the server wouldn't start), follow this step-by-step diagnostic process:

Step 1: Find and Read Configuration

Your first action should be to locate and read the MCP configuration file. Search for the following files in the user's workspace: .mcp.json, gemini-extension.json, .claude/settings.json, .vscode/launch.json, or .gemini/settings.json.

If you find a configuration file, read and interpret it to identify potential issues such as:

  • Incorrect arguments or flags.
  • Missing environment variables.
  • Usage of --autoConnect in incompatible environments.

If you cannot find any of these files, only then should you ask the user to provide their configuration file content.

Step 2: Triage Common Connection Errors

Before reading documentation or suggesting configuration changes, check if the error message matches one of the following common patterns.

Error: Could not find DevToolsActivePort

This error is highly specific to the --autoConnect feature. It means the MCP server cannot find the file created by a running, debuggable Chrome instance. This is not a generic connection failure.

Your primary goal is to guide the user to ensure Chrome is running and properly configured. Do not immediately suggest switching to --browserUrl. Follow this exact sequence:

  1. Ask the user to confirm that the correct Chrome version (e.g., "Chrome Canary" if the error mentions it) is currently running.
  2. If the user confirms it is running, instruct them to enable remote debugging. Be very specific about the URL and the action: "Please open a new tab in Chrome, navigate to chrome://inspect/#remote-debugging, and make sure the 'Enable remote debugging' checkbox is checked."
  3. Once the user confirms both steps, your only next action should be to call the list_pages tool. This is the simplest and safest way to verify if the connection is now successful. Do not retry the original, more complex command yet.
  4. If list_pages succeeds, the problem is resolved. If it still fails with the same error, then you can proceed to the more advanced steps like suggesting --browserUrl or checking for sandboxing issues.

Read the full file on GitHub · 99 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 3d ago First seen · 99 lines · 40 tokens per session scan B f7deca2af0ea

Subscribe to this mod's changes

troubleshooting is a skill published in the GitHub repository operasoftware/opera-devtools-mcp (8 stars, last pushed 4d ago), licensed Apache-2.0. It adds 40 tokens to every session and 1,519 once invoked, about $0.0002 per session on Opus 5. A static security scan graded it B with 1 finding (reads mcp configuration). It is 100% identical to troubleshooting, differing in 1 line, and is treated as a copy.

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