Chrome Devtools

Chrome DevTools

A specialized skill for controlling and inspecting a live Chrome browser. This skill leverages the chrome-devtools MCP server to perform a wide range of browser-related tasks, from simple navigation to complex performance profiling.

Core Process

1. Context Awareness: Always run list_pages and select_page if you are unsure which tab is currently active.
2. Visual Inspection: Take a new take_snapshot after any major navigation or DOM change to get updated uid values.
3. Execution: Perform interactions using uid or wait_for specific text to appear.
4. Validation: Use screenshots sparingly for visual verification, but rely on snapshots for logic.

Core Principles

• Snapshot-First Identification: Always prefer take_snapshot over take_screenshot for finding elements. The snapshot provides uid values required by interaction tools.
• Troubleshoot Objectively: When a page fails, check both console logs (list_console_messages) and network requests (list_network_requests).
• Profile Methodically: Use performance_start_trace and performance_analyze_insight to identify LCP issues or layout shifts.

When to Use

Use this skill when:

• Browser Automation: Navigating pages, clicking elements, filling forms, and handling dialogs.
• Visual Inspection: Taking screenshots or text snapshots of web pages.
• Debugging: Inspecting console messages, evaluating JavaScript in the page context, and analyzing network requests.
• Performance Analysis: Recording and analyzing performance traces to identify bottlenecks and Core Web Vital issues.
• Emulation: Resizing the viewport or emulating network/CPU conditions.

Commands / Usage Patterns

Navigation & Page Management

• new_page: Open a new tab/page.
• navigate_page: Go to a specific URL, reload, or navigate history.
• select_page: Switch context between open pages.
• list_pages: See all open pages and their IDs.
• close_page: Close a specific page.
• wait_for: Wait for specific text to appear on the page. Use reasonable timeouts.

Input & Interaction

• click: Click on an element (use uid from snapshot).
• fill / fill_form: Type text into inputs or fill multiple fields at once.
• hover: Move the mouse over an element.
• press_key: Send keyboard shortcuts or special keys (e.g., "Enter", "Control+C").
• drag: Drag and drop elements.
• handle_dialog: Accept or dismiss browser alerts/prompts.
• upload_file: Upload a file through a file input.

Debugging & Inspection

• take_snapshot: Get a text-based accessibility tree (best for identifying elements).
• take_screenshot: Capture a visual representation of the page or a specific element.
• list_console_messages / get_console_message: Inspect the page's console output.
• evaluate_script: Run custom JavaScript in the page context.
• list_network_requests / get_network_request: Analyze network traffic and request details.

Emulation & Performance

• resize_page: Change the viewport dimensions.
• emulate: Throttling CPU/Network or emulating geolocation.
• performance_start_trace: Start recording a performance profile.
• performance_stop_trace: Stop recording and save the trace.
• performance_analyze_insight: Get detailed analysis from recorded performance data.

Tool Categories

1. Navigation & Page Management

• new_page: Open a new tab/page.
• navigate_page: Go to a specific URL, reload, or navigate history.
• select_page: Switch context between open pages.
• list_pages: See all open pages and their IDs.
• close_page: Close a specific page.
• wait_for: Wait for specific text to appear on the page.

2. Input & Interaction

• click: Click on an element (use uid from snapshot).
• fill / fill_form: Type text into inputs or fill multiple fields at once.
• hover: Move the mouse over an element.
• press_key: Send keyboard shortcuts or special keys (e.g., "Enter", "Control+C").
• drag: Drag and drop elements.
• handle_dialog: Accept or dismiss browser alerts/prompts.
• upload_file: Upload a file through a file input.

3. Debugging & Inspection

• take_snapshot: Get a text-based accessibility tree (best for identifying elements).
• take_screenshot: Capture a visual representation of the page or a specific element.
• list_console_messages / get_console_message: Inspect the page's console output.
• evaluate_script: Run custom JavaScript in the page context.
• list_network_requests / get_network_request: Analyze network traffic and request details.

4. Emulation & Performance

• resize_page: Change the viewport dimensions.
• emulate: Throttling CPU/Network or emulating geolocation.
• performance_start_trace: Start recording a performance profile.
• performance_stop_trace: Stop recording and save the trace.
• performance_analyze_insight: Get detailed analysis from recorded performance data.

Workflow Patterns

Pattern A: Identifying Elements (Snapshot-First)

Always prefer take_snapshot over take_screenshot for finding elements. The snapshot provides uid values which are required by interaction tools.

1. `take_snapshot` to get the current page structure.
2. Find the `uid` of the target element.
3. Use `click(uid=...)` or `fill(uid=..., value=...)`.

Pattern B: Troubleshooting Errors

When a page is failing, check both console logs and network requests.

1. `list_console_messages` to check for JavaScript errors.
2. `list_network_requests` to identify failed (4xx/5xx) resources.
3. `evaluate_script` to check the value of specific DOM elements or global variables.

Pattern C: Performance Profiling

Identify why a page is slow.

1. `performance_start_trace(reload=true, autoStop=true)`
2. Wait for the page to load/trace to finish.
3. `performance_analyze_insight` to find LCP issues or layout shifts.

Best Practices

• Context Awareness: Always run list_pages and select_page if you are unsure which tab is currently active.
• Snapshots: Take a new snapshot after any major navigation or DOM change, as uid values may change.
• Timeouts: Use reasonable timeouts for wait_for to avoid hanging on slow-loading elements.
• Screenshots: Use take_screenshot sparingly for visual verification, but rely on take_snapshot for logic.

References

Related Skills

• critical-thinking:

You MUST load this skill when interpreting performance profiles or debugging complex DOM state issues.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: Cogni-AI-OU
• Source: Cogni-AI-OU/cogni-ai-agent-skills
• License: MIT

Install and usage instructions live in the source repository linked above.