Chrome DevtoolsSAFE

Chrome DevTools for coding agents

The instruction file, verbatim from the audited commit — this is the text the model reads, and the surface the audit's instruction layer examines. Quoted here so you can judge it without cloning anything.

---
name: chrome-devtools
description: Uses Chrome DevTools via MCP for efficient debugging, troubleshooting and browser automation. Use when debugging web pages, automating browser interactions, analyzing performance, or inspecting network requests. This skill does not apply to `--slim` mode (MCP configuration).
---

## Core Concepts

**Browser lifecycle**: Browser starts automatically on first tool call using a persistent Chrome profile. Configure via CLI args in the MCP server configuration: `npx chrome-devtools-mcp@latest --help`.
Addional tooling can be enabled by providing the following flags:

- For extension tooling, use the `--categoryExtensions` flag.
- For memory tooling, use the `--memoryDebugging` flag.

**Page targeting**: Page-scoped tools require a `pageId` parameter to target a specific page. Use `list_pages` to see available pages and their IDs (e.g. `pageId: 1`), or use the ID returned when creating a page with `new_page`.
Note: For `evaluate_script`, `pageId` is required when targeting pages. However, when `--categoryExtensions` is enabled, `pageId` is optional so you can pass `serviceWorkerId` instead to evaluate inside an extension background service worker.
**Element interaction**: Use `take_snapshot` to get page structure with element `uid`s. Each element has a unique `uid` for interaction. If an element isn't found, take a fresh snapshot - the element may have been removed or the page changed.

## Workflow Patterns

### Before interacting with a page

1. Navigate: `navigate_page` or `new_page`
2. Wait: `wait_for` to ensure content is loaded if you know what you look for.
3. Snapshot: `take_snapshot` with `pageId` to understand page structure
4. Interact: Use element `uid`s from snapshot for `click`, `fill`, etc., passing the corresponding `pageId`.

### Efficient data retrieval

- Use `filePath` parameter for large outputs (screenshots, snapshots, traces)
- Use pagination (`pageIdx`, `pageSize`) and filtering (`types`) to minimize data
- Set `includeSnapshot: false` on input actions unless you need updated page state

### Tool selection

- **Automation/interaction**: `take_snapshot` (text-based, faster, better for automation)
- **Visual inspection**: `take_screenshot` (when user needs to see visual state)
- **CSS & Styling inspection**: Use `get_css_styles` to inspect matched rules, cascade, and CSS variables. Treat the output as authoritative and complete.
- **Additional details**: Use `evaluate_script` for runtime DOM/JS data not available via `get_css_styles` or `take_snapshot`.

### Parallel execution

You can send multiple tool calls in parallel, but maintain correct order: navigate → wait → snapshot → interact.

### Testing an extension

> **Before proceeding**: Extension tools (`install_extension`, `list_extensions`, etc.) are only available when the MCP server is started with the `--categoryExtensions` flag. If these tools are not in your tool list, stop and ask the user to update their MCP server configuration:
>
> ```json
> {
>   "mcpServers": {
>     "chrome-devtools": {
>       "command": "npx",
>       "args": ["chrome-devtools-mcp@latest", "--categoryExtensions"]
>     }
>   }
> }
> ```
>
> After updating, the user must restart the MCP server (or their AI client) for the change to take effect.

1. **Install**: Use `install_extension` with the path to the unpacked extension.
2. **Identify**: Get the extension ID from the response or by calling `list_extensions`.
3. **Trigger Action**: Use `trigger_extension_action` to open the popup or side panel if applicable.
4. **Verify Service Worker**: Use `evaluate_script` with `serviceWorkerId` (omitting `pageId` and `args`) to check extension state or trigger background actions. When evaluating in a page, pass `pageId` (omitting `serviceWorkerId`).
5. **Verify Page Behavior**: Navigate to a page where the extension operates and use `take_snapshot` to check if content scripts injected elements or modified the page correctly.

## Troubleshooting

If `chrome-devtools-mcp` is insufficient, guide users to use Chrome DevTools UI:

- https://developer.chrome.com/docs/devtools
- https://developer.chrome.com/docs/devtools/ai-assistance

If there are errors launching `chrome-devtools-mcp` or Chrome, refer to https://github.com/ChromeDevTools/chrome-devtools-mcp/blob/main/docs/troubleshooting.md.

SAFEgrade B · trust 89/100 Nothing in the source contradicts what it says it does. Grade A is reserved for packages that have also passed the behavioural sandbox.

What the source does

Filesystem

none-observed

Network

none-observed

Shell

none-observed

Dependencies

pinned

Secrets in source

none-found

Findings (0)

No findings outside the package's declared scope.

Gates applied: no_behavioural_pass.

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