diff --git a/.codecov.yaml b/.codecov.yaml
new file mode 100644
index 0000000..96cf9ea
--- /dev/null
+++ b/.codecov.yaml
@@ -0,0 +1,7 @@
+# https://docs.codecov.com/docs/commit-status#disabling-a-status
+coverage:
+  status:
+    project: off
+    patch: off
+
+comment: false
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 6ef8d1b..a581830 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -14,15 +14,26 @@ jobs:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
       - uses: Swatinem/rust-cache@v2
-      - run: cargo test --features=search,termwiz,termion,arbitrary
+      - name: Install cargo-llvm-cov
+        uses: taiki-e/install-action@cargo-llvm-cov
+      - name: Run tests on Linux or macOS
+        run: |
+          cargo llvm-cov --color always --lcov --output-path lcov.info --features=search,termwiz,termion,arbitrary
+          cargo llvm-cov --color always --no-run
         if: ${{ matrix.os != 'windows-latest' }}
-      - run: cargo test --features=search,termwiz,arbitrary
+      - name: Run tests on Windows
+        run: |
+          cargo llvm-cov --color always --lcov --output-path lcov.info --features=search,termwiz,arbitrary
+          cargo llvm-cov --color always --no-run
         if: ${{ matrix.os == 'windows-latest' }}
       - run: cargo test --no-default-features --features=tuirs-crossterm,search -- --skip .rs
       - run: cargo test --no-default-features --features=tuirs-termion,search -- --skip .rs
         if: ${{ matrix.os != 'windows-latest' }}
       - run: cargo test --no-default-features --features=no-backend,search -- --skip .rs
       - run: cargo test --no-default-features --features=tuirs-no-backend,search -- --skip .rs
+      - uses: codecov/codecov-action@v3
+        with:
+          files: lcov.info
   lint:
     runs-on: ubuntu-latest
     steps:
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index 17c32f6..9fd93aa 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -38,6 +38,14 @@ Note: On Windows, remove `termion` and `tuirs-termion` features from `--features
 If you use [cargo-watch][], `cargo watch-check` and `cargo watch-test` aliases are useful to run checks/tests automatically
 on files being changed.
 
+### Code coverage
+
+Code coverage is monitored on [codecov][].
+
+https://app.codecov.io/gh/rhysd/tui-textarea
+
+When you implement some new feature, consider to add new unit tests which cover your implementation.
+
 ## Print debugging
 
 Since this crate uses stdout, `println!` is not available for debugging. Instead, stderr through [`eprintln!`][eprintln]
@@ -99,3 +107,4 @@ See [README in bench/](./bench/README.md) for more details.
 [criterion]: https://github.com/bheisler/criterion.rs
 [eprintln]: https://doc.rust-lang.org/std/macro.eprintln.html
 [dbg]: https://doc.rust-lang.org/std/macro.dbg.html
+[codecov]: https://about.codecov.io/
diff --git a/README.md b/README.md
index 3230b45..a2befee 100644
--- a/README.md
+++ b/README.md
@@ -3,6 +3,7 @@ tui-textarea
 [![crate][crates-io-badge]][crate]
 [![docs][doc-badge]][doc]
 [![CI][ci-badge]][ci]
+[![coverage][codecov-badge]][codecov]
 
 [tui-textarea][crate] is a simple yet powerful text editor widget like `<textarea>` in HTML for [ratatui][] and [tui-rs][].
 Multi-line text editor can be easily put as part of your TUI application.
@@ -712,6 +713,8 @@ tui-textarea is distributed under [The MIT License](./LICENSE.txt).
 [doc]: https://docs.rs/tui-textarea/latest/tui_textarea/
 [ci-badge]: https://github.com/rhysd/tui-textarea/actions/workflows/ci.yml/badge.svg?event=push
 [ci]: https://github.com/rhysd/tui-textarea/actions/workflows/ci.yml
+[codecov-badge]: https://codecov.io/gh/rhysd/tui-textarea/graph/badge.svg?token=YAA3EVRXAY
+[codecov]: https://codecov.io/gh/rhysd/tui-textarea
 [tui-rs]: https://github.com/fdehau/tui-rs
 [ratatui]: https://github.com/ratatui-org/ratatui
 [crossterm]: https://docs.rs/crossterm/latest/crossterm/