Google Analytics Audit Test #

14

(not set) Hostname

Why It Matters:

Critical to identifying site or site tracking issues as well as identifying fraudulent/fake traffic.

Industries:

All

Checks For:

Accuracy

How accurate is your recent data?

Insight Category:

Behavior

Can you tell what visitors are doing?

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Background

A GA4 audit is essential for uncovering missing insights—key data points that organizations don't yet know and can act upon. A well-done audit evaluates both behavioral tracking and traffic attribution, ensuring each is accurate and useful. It also assesses whether the data collected truly supports business decisions and reporting.

Test Detail

This test checks for sessions in GA4 where the hostname (domain name of the visited page) is shown as (not set). The hostname dimension is critical for:

  • Validating that traffic is coming from the correct domains
  • Detecting spam or misconfigured tracking
  • Identifying cross-domain tracking issues
  • Ensuring you’re only analyzing production traffic (not test, dev, or 3rd-party embeds)

A (not set) hostname usually indicates:

  • The GA4 configuration didn’t register a valid page_location
  • There was a problem during tag firing or page load
  • A spammy or malformed hit was sent from an external source
  • A bot or scraper sent data without proper context

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How to Conduct This Test

Basic Tests

  • In GA4 > Explore, build a Free-form report:
    • Dimensions: Hostname, Session source/medium
    • Metrics: Sessions, Event count
    • Filter for Hostname = (not set)
    • Add a breakdown by Event name or Page location to look for patterns

Advanced QA

  • In BigQuery, use this query:
    SELECT
      event_date,
      COUNT(*) AS event_count
    FROM `your_dataset.events_*`
    WHERE platform IS NULL OR geo.host IS NULL OR geo.host = '(not set)'
    GROUP BY event_date
    ORDER BY event_date DESC;
  • If there’s any meaningful traffic with (not set) as the hostname, there’s likely a tag or bot issue.

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How To Fix

Fixing (not set) hostnames

  • Check that GA4 tags are firing correctly and early enough to capture page_location and hostname
  • In Google Tag Manager, make sure GA4 configuration tags:
    • Use the correct Measurement ID
    • Are not firing before necessary variables are available
  • Look for spammy traffic or fake hits by comparing:
    • (not set) hostnames with strange session sources or referral patterns
  • Use GA4 filters or BigQuery to exclude bad data from reporting
  • Consider implementing server-side tagging to block or validate incoming traffic before it reaches GA4
  • Hire a pro to diagnose and fix the root causes of (not set) hostname issues, and ensure your analytics stay clean and trustworthy.

Tips from a Google Analytics Consultant

Focus on Insights

Every Google Analytics audit should result in a plan for more insights.

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An insight is:

  • something you don't know
  • and can act on to improve performance

The Goal

Identify and remove insight blockers. Don't get tempted to track things you can't act on!

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