A barrel file (export * from "./x" / export { a, b } from "./x") re-exports an unusually large fraction of its directory's exports versus other barrels in the project — the module's real public surface becomes unclear and tree-shaking is defeated, found without a hardcoded threshold.

// mega-barrel/index.ts — re-exports nearly everything in the directory
export * from "./a";
export * from "./b";
export * from "./c";
// ...ten more, while other barrels in the project re-export a handful

Not flagged — a barrel that resolves to the project's (or a workspace package's) published entry point:

// package.json
{ "main": "./index.ts" }

// index.ts — high re-export ratio is intentional here, it's the public API
export * from "./a";
export * from "./b";

Statistics: for every file with at least one re-export, the check computes its re-export count as a fraction of its sibling files' real (non-re-export) exports in the same directory, then flags a barrel whose ratio is more than 3 standard deviations above the mean ratio of all other barrels in the project. Below 5 barrel candidates in the project, or when the ratios' standard deviation is 0 (every barrel has the same ratio), nothing is flagged — there isn't enough variation to call anything an outlier.

Entry-point exclusion: a barrel is excluded entirely (from both flagging and the statistical population) when it resolves as a package.json's published entry point. The check walks up from the barrel file to the nearest package.json and reads main, module, types/typings, and every string reachable inside exports, resolving each relative to the package.json's directory and comparing with file extensions stripped (so "main": "./index.js" matches a same-directory index.ts).

Scope: entry-point matching catches package.json fields that point directly at the source file, a same-directory build artifact, or a compiled output path under a conventional build-directory name (dist, build, lib, out, output) — a project with a separate src/dist split whose main points into dist/index.js still correctly excludes a parallel src/index.ts via a component-wise swap of the build-directory name to src. A types/typings field pointing at a .d.ts declaration file won't match a barrel's .ts source either way, since only the last extension is stripped for comparison — a non-issue since that field wasn't expected to match the analyzed source regardless. A directory whose only files are barrels re-exporting entire subdirectories (no local sibling file with a "real" export of its own) falls back to counting real exports anywhere in the barrel's own subtree instead of being skipped outright, so this mega-barrel-of-barrels shape is still measured against the rest of the project.