diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 82bb918..cab502a 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -29,3 +29,34 @@ jobs:
         run: npm run typecheck
       - name: Run tests
         run: npm test
+
+  test-coverage:
+    name: Test coverage
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
+      - name: Set up Node.js
+        uses: actions/setup-node@395ad3262231945c25e8478fd5baf05154b1d79f # v6.1.0
+        with:
+          node-version: '26.x'
+          cache: 'npm'
+      - name: Install npm dependencies
+        run: npm install
+      - name: Report coverage
+        run: |
+          set -o pipefail
+          npm run test:coverage | tee "$RUNNER_TEMP/coverage.txt"
+          {
+            echo '## Test coverage'
+            echo
+            echo '```'
+            awk '/start of coverage report/{f=1;next} /end of coverage report/{f=0} f' "$RUNNER_TEMP/coverage.txt" | sed 's/^ℹ //'
+            echo '```'
+          } >> "$GITHUB_STEP_SUMMARY"
+      - name: Upload coverage report
+        if: ${{ !cancelled() }}
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+        with:
+          name: coverage
+          path: coverage/
diff --git a/.gitignore b/.gitignore
index 3055d78..94947f7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,3 +3,6 @@
 
 # JSDoc
 /docs
+
+# Test coverage
+/coverage
diff --git a/AGENTS.md b/AGENTS.md
index 934cba3..179c102 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -8,6 +8,10 @@ code in this repository.
 - `npm test` — run the test suite (uses Node's built-in `node --test` runner;
   tests live next to source as `*.test.js`).
 - `npm test -- --watch` — re-run tests on file change.
+- `npm run test:coverage` — run the suite with coverage, printing a report and
+  writing `coverage/lcov.info`. CI runs this in a separate job that posts the
+  report to the run summary and uploads it as an artifact. There is no
+  threshold: coverage is reported, not enforced.
 - `node --test src/main.test.js` — run a single test file. Add
   `--test-name-pattern '<regex>'` to filter by test name.
 - `npm run lint` — Prettier format check + ESLint. `npm run lint:format:fix` and
diff --git a/package.json b/package.json
index de25356..4b5ba99 100644
--- a/package.json
+++ b/package.json
@@ -23,8 +23,10 @@
     "lint:format:fix": "prettier --write .",
     "lint:quality": "eslint .",
     "lint:quality:fix": "eslint --fix .",
+    "pretest:coverage": "node -e \"require('node:fs').mkdirSync('coverage', { recursive: true })\"",
     "release": "release-it --only-version",
     "test": "node --test",
+    "test:coverage": "node --test --experimental-test-coverage --test-reporter=spec --test-reporter-destination=stdout --test-reporter=lcov --test-reporter-destination=coverage/lcov.info",
     "typecheck": "tsc"
   },
   "devDependencies": {