diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 8a069f5..cb203c7 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -20,11 +20,17 @@ npm ci
 npm run lint:md      # markdownlint for docs content
 npm run type-check    # TypeScript without emitting files
 npm test              # Vitest unit tests
+npx vitest run --coverage   # what CI runs: tests plus the coverage gate
 npm run check-links   # internal docs links
 npm run lint          # ESLint for src/
 npm run build         # production build and doc-sync scripts
 ```
 
+The Vitest workflow runs `npx vitest run --coverage`, which fails if coverage
+falls below the thresholds in `vitest.config.ts` (lines, functions, branches,
+statements) across `src/`, `scripts/` and `netlify/`. Add tests alongside new
+code in those directories.
+
 To preview the docs locally while editing, run:
 
 ```bash