The Klaviyo Experiment Lab
Subject line
entropy
score.
Your list habituates to predictable subject line patterns. Sensory adaptation – a real neurological process – causes open rates to decay when the brain starts pre-categorising your emails before they are even opened. This tool measures how predictable your subject lines are, and tells you where to vary them.
// Based on Shannon entropy – the same information theory used in signal processing and data compression. See Experiment 04 for the full methodology.
// Paste your last 10-30 subject lines – one per line
High entropy
0.00
/ 1.00
// What to do about it
// Your subject lines – classified
| Subject line | Case | Length | Punctuation | Opens with | Tone signal |
|---|
// Methodology note
Entropy is calculated using Shannon's formula H = -Σ p(x) log₂ p(x) across five dimensions: capitalisation pattern, word count, punctuation, opening word type, and tone signal. Each dimension is normalised to a 0-1 scale. The overall score is the mean across all five dimensions. A score above 0.65 indicates sufficient variety to avoid habituation. This is a novel application of established information theory to email marketing – the dimension weightings and threshold values reflect experimental findings from the Poisondart lab rather than published academic research.
// the experiment behind this
Your list is habituating to your patterns.
The Subject Line Entropy Experiment measures open rate decay slope against entropy score across your full sending history. Book the diagnostic audit and we will run it on your account – with real send data, not a sample.
Book the diagnostic audit →
See Experiment 04