A p95 alert says
“The slow 5% crossed 1 second.”
Shape of the tail. Silent when requests fail fast.
An Apdex alert says
“One request in five was slow or broken.”
Size of the tail, counting failures as unhappy users.
## The score in one line
Apdex compresses a latency distribution into a single number between
Apdex = (satisfied + 0.5 × tolerating) / total
Always between 0 and 1. Both boundaries come from the single value you set for T.
Counting failures as frustrated is what makes this worth alerting on. A dependency that starts failing 15% of requests in 40ms makes your p95 _faster_, so a latency alert stays quiet while Apdex falls from 0.97 to about 0.83.
[**What is Apdex?**](/guides/what-is-apdex) walks through the formula, a worked example, and where Apdex and latency percentiles disagree. The rest of this page is the Maple-specific part: picking T for a rule, and building it.
## Choosing T for the rule
0.94 – 1.00
Healthy, with a normal slow tail.
0.85 – 0.94
Degraded, and users can feel it.
below 0.80
The common alerting line. Roughly a fifth of traffic is frustrated or worse.
below 0.50
Most requests are failing or timing out.
0.8 is a common convention. Set the threshold from where your service sits when it is healthy, and how far it has to fall before you would want to be woken up.
## Setting up an Apdex alert in Maple
Maple computes Apdex over the entry-point spans of a service: server spans, consumer spans and trace roots. The service's Apdex chart draws the same set of requests, so a rule you build here matches the chart.
### 1. Start from the Low Apdex score template
Open **Alerts → New rule**. Starting from a service page instead (**Services → your service → Create Alert**) pre-fills the scope.
The rule builder opens on **Start with a template**. Pick