diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index b177e2e..04d66cc 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -9,6 +9,13 @@ jobs:
   pytest:
     name: Pytest
     runs-on: ubuntu-latest
+    permissions:
+      # contents: write lets the action store coverage data and the badge on
+      # its data branch (on push to master). pull-requests: write lets it post
+      # the coverage comment on pull requests. Note: fork PRs get a read-only
+      # token from GitHub regardless, so they will not receive a comment.
+      contents: write
+      pull-requests: write
     steps:
       - uses: actions/checkout@v4
 
@@ -21,4 +28,9 @@ jobs:
         run: pip install -e ".[dev]"
 
       - name: Run pytest
-        run: pytest
+        run: pytest --cov=mergai --cov-report=term-missing
+
+      - name: Coverage comment
+        uses: py-cov-action/python-coverage-comment-action@v3
+        with:
+          GITHUB_TOKEN: ${{ github.token }}
diff --git a/README.md b/README.md
index 2a68b59..e3f0c0b 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # mergai
 
-[![Format Check](https://github.com/Percona-Lab/mergai/actions/workflows/format-check.yml/badge.svg)](https://github.com/Percona-Lab/mergai/actions/workflows/format-check.yml) [![Lint](https://github.com/Percona-Lab/mergai/actions/workflows/lint.yml/badge.svg)](https://github.com/Percona-Lab/mergai/actions/workflows/lint.yml) [![Dependency Check](https://github.com/Percona-Lab/mergai/actions/workflows/deps-check.yml/badge.svg)](https://github.com/Percona-Lab/mergai/actions/workflows/deps-check.yml) [![Security Scan](https://github.com/Percona-Lab/mergai/actions/workflows/security.yml/badge.svg)](https://github.com/Percona-Lab/mergai/actions/workflows/security.yml)
+[![Format Check](https://github.com/Percona-Lab/mergai/actions/workflows/format-check.yml/badge.svg)](https://github.com/Percona-Lab/mergai/actions/workflows/format-check.yml) [![Lint](https://github.com/Percona-Lab/mergai/actions/workflows/lint.yml/badge.svg)](https://github.com/Percona-Lab/mergai/actions/workflows/lint.yml) [![Dependency Check](https://github.com/Percona-Lab/mergai/actions/workflows/deps-check.yml/badge.svg)](https://github.com/Percona-Lab/mergai/actions/workflows/deps-check.yml) [![Security Scan](https://github.com/Percona-Lab/mergai/actions/workflows/security.yml/badge.svg)](https://github.com/Percona-Lab/mergai/actions/workflows/security.yml) [![Coverage](https://raw.githubusercontent.com/Percona-Lab/mergai/python-coverage-comment-action-data/badge.svg)](https://htmlpreview.github.io/?https://github.com/Percona-Lab/mergai/blob/python-coverage-comment-action-data/htmlcov/index.html)
 
 A CLI tool for AI-assisted merge conflict resolution, designed for maintaining long-running forks that regularly sync with upstream repositories.
 
diff --git a/pyproject.toml b/pyproject.toml
index 2219975..69a3a0e 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -44,11 +44,18 @@ dev = [
     "pip-audit>=2.7.0",
     "deptry>=0.12.0",
     "pytest>=7.0.0",
+    "pytest-cov>=5.0.0",
 ]
 
 [tool.pytest.ini_options]
 testpaths = ["tests"]
 
+[tool.coverage.run]
+# relative_files is required by python-coverage-comment-action so the
+# recorded paths match across the CI checkout and the reporting workflow.
+relative_files = true
+source = ["mergai"]
+
 [tool.black]
 line-length = 88
 target-version = ['py310']
@@ -98,4 +105,4 @@ exclude = [
 [tool.deptry]
 # Ignore dev tools that are CLI-based and not imported in code
 [tool.deptry.per_rule_ignores]
-DEP002 = ["pre-commit", "ruff", "mypy", "types-PyYAML", "pip-audit", "deptry", "pytest"]
\ No newline at end of file
+DEP002 = ["pre-commit", "ruff", "mypy", "types-PyYAML", "pip-audit", "deptry", "pytest", "pytest-cov"]
\ No newline at end of file