diff --git a/.github/workflows/l3build.yml b/.github/workflows/l3build.yml
index 11faaf5..ab10d84 100644
--- a/.github/workflows/l3build.yml
+++ b/.github/workflows/l3build.yml
@@ -1,5 +1,27 @@
+# (The MIT License)
+#
+# Copyright (c) 2021-2024 Yegor Bugayenko
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the 'Software'), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+---
 name: l3build
-on:
+'on':
   push:
     branches: master
   pull_request:
diff --git a/.github/workflows/yamllint.yml b/.github/workflows/yamllint.yml
new file mode 100644
index 0000000..a6b7216
--- /dev/null
+++ b/.github/workflows/yamllint.yml
@@ -0,0 +1,15 @@
+---
+name: yamllint
+'on':
+  push:
+    branches:
+      - master
+  pull_request:
+    branches:
+      - master
+jobs:
+  yamllint:
+    runs-on: ubuntu-22.04
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ibiqlik/action-yamllint@v3
diff --git a/.rultor.yml b/.rultor.yml
index 179e3a0..b97b6ef 100644
--- a/.rultor.yml
+++ b/.rultor.yml
@@ -1,5 +1,27 @@
+# (The MIT License)
+#
+# Copyright (c) 2021-2024 Yegor Bugayenko
+#
+# Permission is hereby granted, free of charge, to any person obtaining a copy
+# of this software and associated documentation files (the 'Software'), to deal
+# in the Software without restriction, including without limitation the rights
+# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+# copies of the Software, and to permit persons to whom the Software is
+# furnished to do so, subject to the following conditions:
+#
+# The above copyright notice and this permission notice shall be included in all
+# copies or substantial portions of the Software.
+#
+# THE SOFTWARE IS PROVIDED 'AS IS', WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+# SOFTWARE.
+---
 docker:
-  image: yegor256/rultor-image:1.22.0
+  image: yegor256/rultor-image:1.23.1
 install: |-
   gem install texsc:0.6.0
   gem install texqc:0.6.0