What This Rule Detects

Identifies when UTM parameters use system-reserved keywords that GA4 uses internally to represent missing or untagged data. Using values like "null", "undefined", "(not set)", "(none)", "n/a", or "na" as utm_source makes your paid campaigns indistinguishable from actual untagged traffic, causing them to disappear from attribution reports.

Why It Matters

Business Impact:

• Paid campaigns invisible - Advertising spend appears to have zero results
• Budget allocation destroyed - Cannot measure which sources drive revenue
• ROI calculation impossible - Paid traffic looks identical to missing/untagged traffic
• Reporting shows "missing data" - Your tagged campaigns appear as data quality issues

Technical Impact:

• GA4 uses these keywords internally to represent MISSING attribution data
• When you use them as utm_source, GA4 cannot distinguish your PAID traffic from UNTAGGED traffic
• Reports show your campaigns as "(not set)" - looks like tracking failure, not active campaign
• Data exports contain your expensive ad traffic in "unknown source" rows

Real Example:

• Developer uses utm_source=null as placeholder, forgets to change it
• Launches $15,000 Google Ads campaign
• GA4 reports show:
  • Traffic source: "(not set)" or "null"
  • Indistinguishable from actual untagged/direct traffic
  • Campaign appears to have zero conversions
• Reality: Campaign drove 200 conversions, but data looks like tracking error
• Result: Marketing manager pauses "broken" campaign, wasting $15,000 budget

Common Scenarios

Scenario 1: Development Placeholder Left in Production

Developer uses "null" as temporary value during testing:

Scenario 2: Unknown Source Placeholder

Using "(none)" when actual source is uncertain:

Scenario 3: Not Applicable Shorthand

Using "n/a" when source doesn't seem to fit categories:

How to Fix

Step 1: Identify All Reserved Keywords in Your UTM Parameters

Complete list of GA4 system-reserved values (NEVER use these):

ABSOLUTELY FORBIDDEN:
├── null              → GA4 internal for missing data
├── undefined         → JavaScript/system null state
├── (not set)         → GA4 placeholder for missing values
├── (none)            → GA4 placeholder for absent data
├── n/a               → Commonly confused with "not applicable"
├── na                → Abbreviation of "not applicable"
├── not set           → Variation of "(not set)"
├── not provided      → GA historical keyword (deprecated)
├── (direct)          → GA4 reserved for Direct traffic
└── unknown           → System placeholder (avoid)

Why these are forbidden:

• GA4 uses these INTERNALLY to represent data quality issues
• Your paid campaigns become invisible in reports
• Appear identical to actual untagged/broken tracking
• Cannot be filtered out (mixed with real missing data)

Step 2: Search for Reserved Keywords in Active Campaigns

Manual audit across platforms:

Google Ads:

1. Campaigns → All campaigns
2. Click "Columns" → Modify columns → Add "Final URL"
3. Search for: "null", "undefined", "none", "n/a"
4. Review tracking templates for reserved keywords

Facebook Ads:

1. Ads Manager → Campaigns
2. Check URL parameters on each campaign
3. Search campaign URLs for reserved keywords

Email platforms (Mailchimp, Constant Contact, SendGrid):

1. Review email templates
2. Check all link tracking parameters
3. Verify utm_source not using reserved values

Partner/affiliate links:

1. Request current link formats from partners
2. Check for placeholder values
3. Provide correct utm_source alternatives

Step 3: Replace Reserved Keywords with Descriptive Source Names

Replacement strategy:

If using "null" or "undefined":

❌ utm_source=null
✅ utm_source=`{actual_platform_name}`

Examples:
- utm_source=partner-website
- utm_source=email-signature
- utm_source=qr-code-flyer

If using "(none)" or "n/a":

❌ utm_source=(none)
✅ utm_source=`{specific_identifier}`

Examples:
- utm_source=offline-event
- utm_source=podcast-mention
- utm_source=print-magazine

If using "unknown":

❌ utm_source=unknown
✅ Identify actual source before launching campaign

If truly unknown, use:
- utm_source=organic (for unpaid)
- utm_source=other (last resort, but track separately)

Step 4: Update All Active Campaign Links

Platform-specific update instructions:

Google Ads:

1. Go to affected campaigns
2. Settings → Campaign URL options
3. Update "Final URL suffix" or "Tracking template"
4. Replace: utm_source=null → utm_source=google
5. Save and verify changes

Facebook Ads:

1. Edit each affected ad
2. Update URL parameters
3. Replace: utm_source=undefined → utm_source=facebook
4. Publish changes

Email campaigns:

1. Update email templates
2. Replace reserved keywords with email platform name
3. Example: utm_source=mailchimp, utm_source=constant-contact
4. Test send to verify parameters

Partner links:

1. Contact partners using reserved keywords
2. Provide corrected links with proper utm_source
3. Example: utm_source=partner-name-blog

Step 5: Implement Validation Before Launch

Pre-launch checklist:

Before launching any campaign, verify:
☐ utm_source is NOT any reserved keyword
☐ utm_source describes actual traffic source
☐ utm_source is specific (not "web", "link", "campaign")
☐ No parentheses in values: (none), (not set)
☐ No programming terms: null, undefined, n/a
☐ Test in GA4 Real-Time report to confirm proper attribution

Use validation tools:

• Google Campaign URL Builder (validates format)
• UTMGuard audits (detects reserved keywords automatically)
• Create team documentation listing forbidden keywords

Examples

❌ Incorrect Examples

Using "null" as utm_source:
?utm_source=null&utm_medium=cpc&utm_campaign=google-ads-summer
Result: GA4 shows as "(not set)" or "null" in reports
Impact: Indistinguishable from actual missing data
Action: Campaign appears broken, gets paused

Using "(none)" as utm_source:
?utm_source=(none)&utm_medium=email&utm_campaign=weekly-digest
Result: Appears as missing source attribution
Impact: Email campaign invisible in source reports
Action: Cannot measure email campaign performance

Using "undefined" as utm_source:
?utm_source=undefined&utm_medium=social&utm_campaign=instagram
Result: Shows as system error in GA4
Impact: Looks like tracking failure, not active campaign
Action: Traffic appears as data quality issue

✅ Correct Examples

Specific source instead of "null":
?utm_source=partner-techcrunch&utm_medium=referral&utm_campaign=guest-article-jan
Result: Clearly shows traffic from TechCrunch partnership
Impact: Can measure partner referral performance
Action: Proper attribution, can calculate partnership ROI

Email platform name instead of "(none)":
?utm_source=mailchimp&utm_medium=email&utm_campaign=weekly-newsletter-2024-q1
Result: Shows Mailchimp as source in reports
Impact: Can compare email platform performance
Action: Email campaign tracked correctly

Platform name instead of "undefined":
?utm_source=instagram&utm_medium=social&utm_campaign=product-launch-stories
Result: Instagram identified as traffic source
Impact: Can analyze Instagram story campaign performance
Action: Full attribution with campaign-level ROI visibility

GA4 Impact Analysis

Traffic Source Reports:

• Reserved keywords → Appears as "(not set)" or system placeholder
• Proper source names → Appears as distinct traffic source
• Impact: Campaign visibility vs invisibility

Channel Grouping:

• Reserved keywords → May classify as "Unassigned" or "Direct"
• Proper naming → Classified correctly based on utm_medium
• Impact: Channel analysis broken vs working

Conversion Attribution:

• Reserved keywords → Conversions attributed to "(not set)"
• Proper naming → Conversions attributed to actual campaign
• Impact: ROI invisible vs measurable

Data Quality:

• Reserved keywords → Appears as data quality issue
• Proper naming → Appears as valid campaign traffic
• Impact: Looks like broken tracking vs successful campaign

Detection in UTMGuard

UTMGuard automatically detects reserved keywords in UTM parameters:

1. Scans all utm_source, utm_medium, utm_campaign values
2. Compares against list of GA4 system-reserved keywords
3. Flags any usage of forbidden values
4. Counts affected sessions
5. Reports specific campaigns using reserved keywords with priority ranking

Audit Report Shows:

• Total sessions using reserved keywords
• Which reserved keyword was used
• Affected campaigns and URLs
• Estimated advertising spend with broken attribution
• Priority ranking by traffic volume

Related Validation Rules

Frequently Asked Questions

Q: What if I already launched campaigns with reserved keywords?

A: Update the URLs immediately. Historical data cannot be fixed, but stopping the issue prevents further data corruption. Create a GA4 annotation marking when you fixed it to explain data discontinuity.

Q: Can I use "Other" as a utm_source?

A: Technically yes, but not recommended. "Other" is vague and makes reporting unclear. Use a specific identifier instead. Example: Instead of "other", use "offline-event" or "podcast-mention" or "print-ad".

Q: Will GA4 reject reserved keywords or just misclassify them?

A: GA4 will NOT reject them. It accepts the value but treats it identically to actual missing data, making your campaigns invisible. This is why detection is critical - the tracking "works" but data is unusable.

Q: Are reserved keywords case-sensitive?

A: No. "null", "Null", and "NULL" are all problematic. GA4 treats them as the same reserved value. Avoid all variations.

Q: What about "direct" as a utm_source?

A: Never use it. "(direct)" is GA4's reserved value for traffic with no source attribution (typed URL, bookmarks). Using utm_source=direct contradicts the purpose of UTM tagging.

Q: Can I use "not-applicable" with hyphens instead of "n/a"?

A: Still not recommended. While technically different, it suggests you don't know the source. Every campaign should have a specific, identifiable source. If truly unsure, delay launch until source is determined.

Q: How do I handle QR codes where source is ambiguous?

A: QR codes are the source. Use: utm_source=qr-code-{location} and utm_medium=offline or utm_medium=print. Example: utm_source=qr-code-flyer&utm_medium=print&utm_campaign=local-event-jan.

Q: What if my development team uses "null" in testing environments?

A: Acceptable for dev/staging environments ONLY. Implement validation that blocks deployment to production if reserved keywords detected. Use environment-specific URL builders that enforce proper naming in production.

External Resources

• GA4: Traffic Source Dimensions
• Google: Campaign URL Builder
• Best Practices for UTM Parameters
• GA4: Default Channel Grouping