regex-specificity

A fast, heuristic-based library to calculate the specificity of a regular expression pattern against a specific string.

Concept

Specificity measures how "precise" a match is. For example, the pattern abc is more specific to the string "abc" than the pattern a.c or .*.

The calculation follows these principles:

1. Positional Weighting: Earlier matches contribute more to the total score than later ones.
2. Certainty: Literals (exact characters) score higher than character classes or wildcards.
3. Information Density: Narrower character classes (e.g., [a-z]) score higher than broader ones (e.g., .).
4. Branching Penalty: Patterns with many alternatives (alternations) are penalized as they are less specific.

Usage

⚠️ Warning

The get function assumes that the string provided is already a full match for the pattern. If the pattern does not match the string, the resulting score will be mathematically inconsistent and meaningless for comparison purposes.

use regex_specificity::get;

fn main() {
    let string = "abc";
    let high = get(target, "abc").unwrap();
    let low = get(target, ".*").unwrap();
    assert!(high > low);
}

License

This project is licensed under the MIT License © 2025 557.