wct-istanbul is a plugin for the Web Component Tester ( wct ) that adds Istanbul‑based code‑coverage collection and reporting to any project tested with wct. It instruments JavaScript (including ES2015+, modules, async/await, etc.), generates reports (text‑summary, lcov, etc.) in a configurable folder, and can enforce global coverage thresholds, making it useful for front‑end developers who need automated coverage metrics for Polymer/Web Component test suites.