Screenshot Eval

Screenshot Evaluation Skill

Activation: screenshot evaluation, error detection, browser testing, UI verification, feature validation, console errors, network failures

Overview

This skill provides a systematic approach to evaluating browser state during testing. It ensures features actually work by checking for console errors, network failures, and visual error indicators before declaring success.

Critical Rule: A feature is NOT complete until browser testing passes with no errors.

Evaluation Checklist

Execute these steps in order after navigating to the page or completing an action:

Step 1: Check Console for Errors

Use mcp__playwright__browser_console_messages with level="error"

Pass criteria:

• No console errors related to your feature
• React errors (component crashes) = FAIL
• Network/fetch errors = FAIL
• TypeScript/undefined errors = FAIL

Acceptable errors (can ignore):

• Third-party script warnings (analytics, etc.)
• Deprecated API warnings not related to your code

Step 2: Check Network Requests

Use mcp__playwright__browser_network_requests

Pass criteria:

• All API requests return 2xx status codes
• No 4xx errors (except expected 401/403 for auth tests)
• No 5xx server errors
• All requests complete (no pending/cancelled)

Check specifically:

• Your API endpoints return expected data
• Static assets load successfully
• WebSocket connections establish if needed

Step 3: Take Accessibility Snapshot

Use mcp__playwright__browser_snapshot

Error patterns to look for in snapshot:

Step 4: Take Screenshot Proof

Use mcp__playwright__browser_take_screenshot

This screenshot is REQUIRED evidence that the feature works:

• Shows the expected UI state
• Proves the feature rendered correctly
• Attached to PR or issue as verification

Pass/Fail Criteria

PASS - All conditions met:

• No console errors (Step 1)
• All network requests succeeded (Step 2)
• No error patterns in snapshot (Step 3)
• Screenshot shows expected state (Step 4)

FAIL - Any condition:

• Console errors present
• Network requests failed (4xx/5xx)
• Error patterns detected in snapshot
• UI shows error state or missing content

Example Evaluation Workflow

Testing a New Feature

## Feature: Create Shootout Form

1. Navigate to /builder
   → mcp__playwright__browser_navigate url="/builder"

2. Check for errors after page load
   → mcp__playwright__browser_console_messages level="error"
   ✓ No console errors

3. Check network requests
   → mcp__playwright__browser_network_requests
   ✓ All 200 OK

4. Take snapshot, verify form elements
   → mcp__playwright__browser_snapshot
   ✓ Form visible with expected fields

5. Fill form and submit
   → mcp__playwright__browser_fill_form
   → mcp__playwright__browser_click (submit button)

6. Check for errors after submission
   → mcp__playwright__browser_console_messages level="error"
   ✓ No console errors

7. Check API call succeeded
   → mcp__playwright__browser_network_requests
   ✓ POST /api/v1/shootouts returned 201

8. Verify success state
   → mcp__playwright__browser_snapshot
   ✓ Success message visible OR redirected to new shootout

9. Take final screenshot proof
   → mcp__playwright__browser_take_screenshot
   ✓ Screenshot captured

Debugging a Failure

When evaluation fails:

1. Console error? → Check the error message, fix the code
2. Network failure? → Check backend logs, verify endpoint exists
3. Error in snapshot? → Identify the component showing error, trace the cause
4. Infinite loading? → Check if API call returned, verify data handling

MCP Tools Reference

Playwright (PR Verification)

Chrome DevTools (Deep Debugging)

When Playwright checks show errors, use Chrome DevTools for deeper investigation:

Workflow: Playwright finds issue → Chrome DevTools investigates → Fix code → Playwright verifies

Integration with /merge Command

The /merge command enforces this evaluation before PR creation:

1. Runs quality gates (tests, lint, build)
2. Requires browser testing using this skill
3. Checks console for errors
4. Checks network for failures
5. Captures screenshot proof
6. Includes evidence in PR body

Never bypass browser testing - unit tests passing does NOT mean the feature works.

Common Issues and Solutions

React Error Boundary Triggered

• Check for unhandled promises
• Verify data shape matches component expectations
• Check for null/undefined access

API Returns 404

• Verify endpoint URL is correct
• Check if backend route exists
• Verify path parameters are valid

API Returns 500

• Check backend container logs
• Verify database migrations ran
• Check for missing environment variables

Infinite Loading

• API might be hanging - check backend
• Data might not trigger render - check state updates
• WebSocket might not connect - check connection setup

Empty Content

• API might return empty array - verify test data exists
• Conditional rendering might hide content - check conditions
• Data might be undefined - check fetch success