Fix Truncated Event Names in GA4
The Case File: Event Name Truncation
Your GA4 property is collecting events, but something is quietly breaking in the background. Event names exceeding 40 characters are being truncated, and this silent data corruption is creating inconsistencies across your analytics reports.
When an event name surpasses GA4's 40-character limit, the platform automatically truncates it to the first 40 characters. This means button_click_homepage_hero_section_learn_more becomes button_click_homepage_hero_section_le—a meaningless string that undermines your entire event taxonomy.
The symptom is subtle but destructive: events appear in your reports with shortened names, making them difficult to identify. Worse, if you've marked a truncated event as a key event (conversion), GA4 will not report it as a key event at all because the system appends "_c" to conversion event names, pushing the total length beyond the limit.
The Root Causes: Why Event Names Get Too Long
1. Universal Analytics Migration Baggage
Many organizations migrated from Universal Analytics to GA4 without reconsidering their event naming structure. UA allowed for Category/Action/Label combinations that could be quite verbose. Teams often concatenated these elements into single event names for GA4, creating monsters like ecommerce_product_detail_view_add_to_cart_button_clicked.
According to official Google documentation, event names must be 40 characters or fewer. This is a hard limit that cannot be increased, even with Google Analytics 360.
2. Over-Descriptive Naming Conventions
The desire for self-documenting event names leads to excessive verbosity. Developers and analysts create names that describe every aspect of the interaction: video_play_homepage_above_fold_product_demo_autoplay. While the intention is clarity, the result is truncation and confusion.
3. Dynamic Event Name Construction in GTM
Google Tag Manager implementations often use dynamic variable concatenation to build event names. A common pattern looks like this:
Copy code
{{Page Type}}_{{Action}}_{{Element ID}}_{{User Status}}
When each variable contains lengthy values, the resulting event name easily exceeds 40 characters. For example: product_detail_page_button_click_add_to_cart_premium_logged_in_user clocks in at 73 characters.
4. Data Layer Inconsistencies
Developers may push event names to the data layer without validation. If the data layer structure includes nested properties or auto-generated identifiers, event names can balloon unexpectedly:
javascriptCopy code
dataLayer.push({
'event': 'form_submission_contact_us_enterprise_sales_inquiry_form'
});
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5. Lack of Event Naming Governance
Without a documented event taxonomy and naming conventions, different teams create events independently. Marketing wants campaign_click_summer_sale_2024_banner_homepage, while product teams use user_interaction_feature_discovery_onboarding_tooltip_dismissed. The absence of governance creates a wild west of event names.
6. Platform-Specific Quirks
GA4's event modification feature (Admin > Events > Modify event) allows you to rename events post-collection, but if you create a modified event name that exceeds 40 characters, the same truncation issue occurs. This catches many analysts off guard who assume the Admin interface would prevent the error.
The "So What?": Business Impact of Truncated Events
Key Events (Conversions) Fail Silently
This is the most critical impact. According to Google's official documentation: "If you mark an event as a key event and the event exceeds 40 characters, then the event will not be reported as a key event."
When GA4 marks an event as a key event, it appends "_c" to create a conversion event. If your original event name is 39 characters, adding "_c" pushes it to 41 characters, breaking the key event tracking entirely. Your conversion reporting becomes incomplete, directly impacting:
ROAS calculations in Google Ads
Attribution modeling accuracy
Funnel analysis completeness
Executive dashboards showing conversion metrics
Data Fragmentation and Reporting Chaos
Truncated event names create multiple versions of what should be the same event. Consider these scenarios:
button_click_homepage_hero_section_learn_more (45 chars) becomes button_click_homepage_hero_section_le
button_click_homepage_hero_section_sign_up (44 chars) becomes button_click_homepage_hero_section_si
Both appear as separate events in reports, but the truncated names are indistinguishable from each other and from other similarly truncated events. This makes it impossible to analyze user behavior accurately.
Audience Building Failures
GA4 audiences rely on specific event names for segmentation. If you create an audience based on user_completed_onboarding_tutorial_step_five, but the actual event is truncated to user_completed_onboarding_tutorial_st, your audience will never populate. This breaks:
Remarketing campaigns
Personalization strategies
Cohort analysis
Lifecycle marketing automation
BigQuery Export Complications
For organizations using the GA4 BigQuery export, truncated event names create query complexity. Analysts must account for truncation when writing SQL queries, adding LENGTH() checks and substring matching that shouldn't be necessary.
The Investigation: How to Detect Truncated Events
Method 1: GA4 Reports Interface
Navigate to Reports > Engagement > Events in your GA4 property. Look for event names that:
End abruptly mid-word (e.g., button_click_homepage_hero_section_le)
Appear to be cut off at exactly 40 characters
Have similar prefixes but different, nonsensical endings
Add a secondary dimension of "Event count" and sort by event name alphabetically. Truncated events will cluster together, making patterns visible.
Method 2: GA4 DebugView
Enable DebugView (Configure > DebugView) and trigger events on your site while monitoring in real-time. DebugView displays the full event name as it's collected. Compare what you see in DebugView to what appears in standard reports after 24-48 hours.
To enable DebugView:
Install the Google Analytics Debugger Chrome extension, or
Add ?debug_mode=true to your URL parameters, or
For GTM implementations, create a debug_mode parameter set to true
Method 3: Explore Reports with Event Name Length
Create a custom Exploration report:
Go to Explore in the left navigation
Create a new Free form exploration
Add Event name as a dimension
Create a custom metric using the formula: LENGTH(Event name)
Filter for event names where length = 40
Any event showing exactly 40 characters is likely truncated.
Method 4: BigQuery SQL Query
If you have the BigQuery export enabled, run this query to identify potentially truncated events:
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SELECT
event_name,
LENGTH(event_name) as name_length,
COUNT(*) as event_count
FROM
`your-project.analytics_XXXXX.events_*`
WHERE
_TABLE_SUFFIX BETWEEN FORMAT_DATE('%Y%m%d', DATE_SUB(CURRENT_DATE(), INTERVAL 30 DAY))
AND FORMAT_DATE('%Y%m%d', CURRENT_DATE())
AND LENGTH(event_name) = 40
GROUP BY
event_name, name_length
ORDER BY
event_count DESC
This query identifies all events with exactly 40 characters collected in the last 30 days—strong candidates for truncation.
Method 5: GTM Preview Mode
If you're using Google Tag Manager, enter Preview mode and trigger events on your site. The GTM debugger shows the exact event name being sent to GA4 before any truncation occurs. Compare these values to what appears in GA4 reports.
Look for the GA4 Event tag in the Tags Fired section and check the Event Name field. If it exceeds 40 characters, you've found the source of truncation.
The Solution: How to Fix Truncated Event Names
Step 1: Audit Your Current Event Taxonomy
Before making changes, document all existing events:
Export your event list from Admin > Events
Use the BigQuery query above to identify truncated events
Create a spreadsheet mapping current (truncated) names to intended (full) names
Prioritize fixing key events first, as these directly impact conversion tracking
Step 2: Establish Event Naming Conventions
Implement a strict naming convention that keeps events under 40 characters:
Recommended Structure:
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{category}_{action}_{context}
Examples:
video_play_homepage (20 chars)
form_submit_contact (19 chars)
btn_click_cta_hero (18 chars)
purchase_complete (17 chars)
Best Practices:
Use abbreviations strategically: btn instead of button, cta instead of call_to_action
Keep category names short: vid for video, frm for form, nav for navigation
Use underscores only (no hyphens or spaces)
Start with a letter (required by GA4)
Use lowercase consistently
Avoid redundant words like "event" or "tracking"
Step 3: Fix GTM Event Tag Configurations
For Google Tag Manager implementations:
Go to Tags in your GTM container
Locate all GA4 Event tags
Check the Event Name field for each tag
If using variables, review the Variables section
For Dynamic Event Names:
Create a Custom JavaScript variable that validates and truncates if necessary:
javascriptCopy code
function() {
var eventName = {{Your Event Name Variable}};
if (eventName.length > 40) {
// Log warning to console
console.warn('Event name exceeds 40 chars:', eventName);
// Return truncated version or throw error
return eventName.substring(0, 40);
}
return eventName;
}
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Better approach: Redesign your event naming logic to never exceed 40 characters in the first place.
Step 4: Document Your Event Taxonomy
Create and maintain a tracking specification document that includes:
Complete list of all event names
Character count for each event
Purpose and trigger conditions
Associated parameters
Implementation location (GTM tag ID, code file, etc.)
Owner/team responsible
Store this in a shared location (Confluence, Google Docs, Notion) and require review before any new events are implemented.
Step 5: Test Everything
After implementing fixes:
Use GTM Preview mode to verify new event names
Monitor DebugView for 24-48 hours to confirm correct collection
Check Reports > Engagement > Events after processing delay
Verify key events appear in Admin > Key events
Confirm audience definitions still work with new event names
Test any Google Ads conversions that rely on these events
Step 6: Clean Up Historical Data (Optional)
You cannot retroactively fix truncated event names in GA4's standard reports, but you can:
Use BigQuery to reprocess historical data with corrected names for custom analysis
Create custom Looker Studio reports that map old truncated names to new correct names using CASE statements
Document the date of the fix so analysts know when the event naming changed
Case Closed: Let Watson Do the Heavy Lifting
Finding truncated event names manually requires systematic checking across multiple GA4 interfaces, GTM containers, and potentially BigQuery exports. For a property with dozens or hundreds of custom events, this investigation can take hours.
The Watson Analytics Detective dashboard spots this Advice-level error instantly, alongside 60+ other data quality checks. Watson automatically scans your GA4 property and flags any event names exceeding 40 characters, showing you:
The exact event names that are truncated
The character length of each problematic event
The count of truncated events in your property
The business impact (especially for key events)
Instead of manually running BigQuery queries or creating custom Exploration reports, Watson presents the issue in a clear, actionable format the moment you connect your GA4 property.
Stop hunting for invisible data quality issues. Let Watson be your analytics detective. Explore Watson Analytics Detective →
