AI Index

A measurement skill: given a text, produce a defensible number for "how AI does this read", and know what that number is worth.

The short version of what the measurements below establish: surface tells are cheap to detect and cheap to remove, so they cannot carry the score. A text with zero surface tells has had its fingerprints wiped, which is not the same as having something to say. The number that matters comes from the judgment layer.

When to use

• Designing or calibrating an AI-likeness score for drafts, submissions, or CI
• Checking a draft before publishing, where "feels AI" needs to become a location and a reason
• Auditing a detector someone else built (the gap check in §4 is the audit)

Not for: deciding whether a person used AI. The measurements here separate unedited model output from human prose. They do not separate a human from a human who edited model output, and §3 shows exactly why.