GA4 Custom Alerts: How to Set Them Up, and What They Will Not Catch
GA4 can email you when a number moves. The feature is called a custom insight, it is free, and most people who run a site have never opened it. This guide sets one up in about five minutes, then is honest about what it will not catch, because that second part is why dedicated monitoring tools exist.
Full disclosure before anything else: this guide lives on the Metrics Watch blog, and Metrics Watch sells a GA4 alerting product. The GA4 instructions below are the same either way, and every GA4 limit quoted here was checked against Google's own documentation on 3 September 2026.
What a GA4 custom alert actually is
Google does not call them alerts. In GA4 the feature is a custom insight: a rule that evaluates one metric on a schedule, and either shows a card on the Insights panel or emails a list of addresses you type in. You can have up to 50 of them per property, and you need the Editor or Administrator role on the property to create one.
Each rule has four parts: how often it runs (hourly, daily, weekly, or monthly), which slice of your data it looks at (all of it, or a segment filtered by a dimension such as country or source/medium), the metric, and the condition. The condition is either a threshold you set (sessions decreased by more than 30 percent, conversions less than 10) or "has anomaly," which lets Analytics decide what counts as unusual against its own model of your history.
Setting one up
- Open the property in GA4 and go to Reports, then the Reports snapshot. Scroll to the Insights card and click View all insights.
- Click Create. Google offers suggested insights first; skip those and choose Create new.
- Pick the evaluation frequency. Hourly is only offered for web data; app events are excluded from hourly checks because collection delays would generate false notifications.
- Choose the segment. "All users" is the default; narrow it by a dimension if the rule is about one campaign or one landing page.
- Choose the metric and the condition. Start with something that describes a real failure, not a slow trend: sessions decreased by 50 percent, or conversions equal to 0.
- Name it, enter the email addresses that should be notified, and save.
The insight is also visible to every user of the property on the Insights panel whether or not they are on the email list, and generated insights are kept for one year.
Three rules worth creating on every property
Conversions equal to 0, checked daily. The cheapest tracking-loss detector there is. If a form or checkout event stops firing, this is the rule that notices.
Sessions decreased by 50 percent, checked hourly. Catches a site outage, a robots.txt mistake, or a tag manager publish that removed the GA4 tag. Hourly is the fastest GA4 offers.
Has anomaly on sessions, checked daily. The catch-all. You will get some noise on the first few weeks while the model learns your traffic shape, and a spike from a mention or a bot is reported the same way as a drop.
What GA4 custom insights will not do
These are the limits as documented, not opinions, and they are the reason a free feature has a paid category next to it.
Email is the only delivery channel. There is no Slack, no webhook, no SMS. If the person who reads that mailbox is on holiday, the alert is read when they are back.
Hourly is the ceiling, and only for web data. A rule cannot run more often than once an hour, and it runs against whatever GA4 has finished processing at that point, which is not real time. A tag that breaks at 9:05 is noticed, at best, sometime after 10:00.
One condition per rule, one metric per condition. "Sessions are normal but conversions dropped" is two rules and two emails, and nothing connects them.
No schedule awareness. There are no quiet hours and no separate thresholds for weekdays and weekends. A rule that is right for Tuesday afternoon fires every Sunday morning, and after the third false alarm people stop reading the email, which is the failure mode that matters.
Fifty per property. Enough for one site. An agency watching 20 client properties is setting up and maintaining rules in 20 places, each needing Editor access.
Where a dedicated monitor fits
If daily email is enough for you, stop here; the three rules above are free and you should have them. A dedicated tool earns its price on the four gaps: speed, channel, schedule, and scale.
Metrics Watch Alerts monitors GA4 traffic, conversions, events, and custom metrics on a 15-minute check on its Basic plan and a 10-minute check on Starter and above. Alerts are delivered by email and, on Starter and above, to Slack, so the person on call sees it where they already are. Each alert can be filtered by any GA4 dimension, can carry different thresholds for weekdays and weekends, and can be silenced during quiet hours you set. Basic is $79 per month ($66 per month paid annually) for 3 alerts; Starter is $99 per month ($83 annually) for 10. The trial needs no credit card, and there is a 30-day money-back guarantee if it does not catch a real problem faster than you would have. Those figures are from the Metrics Watch Alerts page as of 3 September 2026.
It monitors GA4 only. If the thing you are worried about is ad spend on Google Ads or Meta rather than what happens on the site, look at a tool built for ad accounts instead; that is a different job.
Common questions
Do GA4 custom insights cost anything?
No. They are part of every GA4 property, standard or 360.
Can GA4 send alerts to Slack?
Not natively. Custom insights notify by email only. Getting one into Slack means forwarding the email through a rule in your mail client or a third-party connector, and you lose the ability to act on the alert from Slack itself.
How fast will GA4 notice a broken tag?
An hourly custom insight on web data is the fastest option, and it evaluates processed data, not the realtime report. Expect to learn about a break in the following hour at the earliest, often later.
Who is behind Metrics Watch?
A small company, deliberately. It has been reporting on marketing data since 2015, it is run by its owner, and support emails get answered by the person who can actually fix things.
Start with the free rules
Create the three GA4 rules above today; they cost nothing and they catch the obvious failures by the next morning. If "the next morning" is too late for your site, or the alert needs to land in Slack rather than an inbox, set up one alert on Metrics Watch Alerts against the same property and break something on purpose in a test environment; you will know within an hour whether it earns its place.
