GTM Performance Skills¶

Audit Google Tag Manager implementations for performance impact with flexible argument modes.

Skill¶

gtm-performance-audit [options] — Comprehensive GTM performance audit analyzing container size, tag execution, trigger efficiency, and Core Web Vitals impact

Requirements¶

Required: Chrome DevTools MCP Server

This command requires an active Chrome DevTools MCP connection to perform live page profiling.

Flexible Argument Modes¶

Quick Checks During Development¶

/gtm-performance-audit --quick --url=https://example.com
/gtm-performance-audit --quick --scope=current-pr
/gtm-performance-audit --quick --container-id=GTM-ABC123

- Fast container health check (~5 min) - Tag count and container size - Obvious blocking tags

Standard Audits (Default)¶

/gtm-performance-audit --url=https://example.com
/gtm-performance-audit --url=https://example.com --with-container-json=./export.json
/gtm-performance-audit --standard --format=json --url=https://example.com

- Full analysis (~15 min) - All 14 issue detection checks - CWV impact mapping - Tag inventory with timing

Comprehensive Audits (Pre-Launch)¶

/gtm-performance-audit --comprehensive --url=https://example.com
/gtm-performance-audit --comprehensive --format=summary
/gtm-performance-audit --comprehensive --with-container-json=./container.json

- Deep profiling (~30 min) - Custom HTML code review - Server-side migration candidates - Full remediation roadmap

Argument Options¶

Depth Modes¶

--quick - Container size + tag count (~5 min)
--standard - Full analysis with CWV mapping (default, ~15 min)
--comprehensive - Deep profiling + remediation plan (~30 min)

Scope Control¶

--scope=current-pr - Only GTM-related files changed in current PR
--scope=container=<GTM-ID> - Specific GTM container
--scope=entire - Full GTM analysis (default)

Output Formats¶

--format=report - Detailed report with tag inventory (default)
--format=json - JSON for CI/CD integration
--format=summary - Executive summary with key findings

GTM-Specific Options¶

--container-id=<GTM-XXXX> - GTM container ID to audit
--with-container-json=<path> - Path to exported container JSON
--url=<target-url> - Target URL for live profiling

Legacy Focus Options (Still Supported)¶

For backward compatibility, focus areas without -- prefix still work: - container - Container size and structure - tags - Individual tag performance - triggers - Trigger efficiency - datalayer - DataLayer analysis - custom-html - Custom HTML tag audit - consent - Consent mode compliance

What Gets Audited¶

14-Point Issue Detection¶

Synchronous script loading - GTM loaded without async
Blocking tags - Tags blocking main thread >50ms
Large payloads - Tags or container >100KB
Main thread blocking - JavaScript execution blocking interactivity
Missing conditional firing - Tags firing on all pages unnecessarily
Trigger optimization - Expensive DOM selectors and broad rules
Duplicate tags - Same tracking pixel firing multiple times
Orphaned tags - Tags with no active triggers
Expensive variables - Variables with costly DOM lookups
Missing async attribute - Third-party scripts without async/defer
Custom HTML best practices - Inline scripts that could use built-in types
Server-side candidates - Tags eligible for server-side GTM
Consent mode gaps - Tags firing before consent granted
Tag firing order - Critical tags delayed by non-essential tags

CMS-Specific Patterns¶

Drupal¶

google_tag module configuration
Template-level GTM injection
DataLayer hook implementations
Multiple container detection

WordPress¶

GTM4WP plugin settings
header.php manual injection
WooCommerce enhanced ecommerce overhead
Google Site Kit conflicts

CI/CD Integration¶

Export results as JSON for automated pipelines:

# GitHub Actions example
- name: Run GTM audit
  run: /gtm-performance-audit --standard --format=json --url=${{ env.SITE_URL }} > gtm-results.json

- name: Check container size
  run: |
    SIZE=$(jq '.container.size_kb' gtm-results.json)
    if (( $(echo "$SIZE > 100" | bc -l) )); then
      echo "GTM container exceeds 100KB threshold"
      exit 1
    fi

Common Workflows¶

Pre-Commit (GTM config changes):

/gtm-performance-audit --quick --scope=current-pr

PR Review:

/gtm-performance-audit --standard --url=https://staging.example.com

Pre-Launch:

/gtm-performance-audit --comprehensive --url=https://example.com --with-container-json=./export.json

Tag Cleanup Sprint:

/gtm-performance-audit --comprehensive --format=summary

Performance Audit - General performance audit (Core Web Vitals, assets, queries)
Live Site Audit - Comprehensive audit (perf + a11y + security + quality)
Security Audit - Security audit (includes third-party script risks)

See Skills Overview for all available skills.