diff --git a/flake.nix b/flake.nix
index aa172abd..77d9f5d4 100644
--- a/flake.nix
+++ b/flake.nix
@@ -31,6 +31,7 @@
             pkgs.writeShellApplication {
               name = "write";
               text = ''
+                mkdir -p "$(dirname ${path})"
                 cat > ${path} <<'EOF'
                 ${value}
                 EOF
@@ -78,6 +79,23 @@
               description = "write action.yml-s and tables for README-s";
             };
 
+            writeBuildjetCI = writeYAML ".github/workflows/buildjet-ci.yaml" (
+              import ./nix/ci.nix { backend = "buildjet"; }
+            );
+
+            writeActionsCI = writeYAML ".github/workflows/ci.yaml" (
+              import ./nix/ci.nix { backend = "actions"; }
+            );
+
+            writeCI = {
+              text = ''
+                ${lib.getExe config.packages.writeBuildjetCI}
+                ${lib.getExe config.packages.writeActionsCI}
+                npm run format-ci
+              '';
+              description = "write CI files";
+            };
+
             install = {
               runtimeInputs = [ pkgs.nodejs_20 ];
               text = ''npm i'';
@@ -97,7 +115,7 @@
               {
                 prefix = "nix run .#";
                 packages = {
-                  inherit (config.packages) write install build;
+                  inherit (config.packages) write install build writeCI;
                 };
               }
             ];
diff --git a/nix/ci.nix b/nix/ci.nix
new file mode 100644
index 00000000..3221a95a
--- /dev/null
+++ b/nix/ci.nix
@@ -0,0 +1,330 @@
+{ backend }:
+let
+  choose =
+    optionActions: optionBuildjet: if backend == "actions" then optionActions else optionBuildjet;
+
+  backend_ = choose "" ''
+    # use BuildJet backend
+              backend: buildjet'';
+
+  on = choose ''
+    push:
+        # don't run on tags, run on commits
+        # https://github.com/orgs/community/discussions/25615
+        tags-ignore:
+          - "**"
+        branches:
+          - "**"
+      schedule:
+        - cron: 0 0 * * *'' "";
+
+  name = choose "" ''with BuildJet backend'';
+in
+''
+  name: Nix CI ${name}
+  on:
+    ${on}
+    pull_request:
+    workflow_dispatch:
+
+  env:
+    # https://stackoverflow.com/a/71158878
+    git_pull: git pull --rebase origin ''${{ github.head_ref || github.ref_name }}
+    pin_nixpkgs: nix registry pin nixpkgs github:NixOS/nixpkgs/807c549feabce7eddbf259dbdcec9e0600a0660d
+
+  jobs:
+    # Build the action
+    # Commit and push the built code
+    build:
+      name: Build the action
+      runs-on: ubuntu-20.04
+      permissions:
+        contents: write
+        actions: write
+      steps:
+        - uses: actions/checkout@v4
+          with:
+            submodules: true
+
+        - uses: nixbuild/nix-quick-install-action@v27
+
+        - name: Restore and save Nix store
+          uses: ./.
+          with:
+            primary-key: build-''${{ runner.os }}-''${{ hashFiles('**/package-lock.json', 'package.json', 'flake.nix', 'flake.lock') }}
+            paths: |
+              ~/.npm
+            # do purge caches
+            purge: true
+            # purge all versions of the cache
+            purge-prefixes: build-''${{ runner.os }}-
+            # created more than 0 seconds ago relative to the start of the `Post Restore` phase
+            purge-created: 0
+            # except the version with the `primary-key`, if it exists
+            purge-primary-key: never
+            ${backend_}
+
+        # # Uncomment to debug this job
+        # - name: Setup tmate session
+        #   uses: mxschmitt/action-tmate@v3
+
+        - name: Configure git
+          env:
+            # required for gh
+            GITHUB_TOKEN: ''${{ secrets.GITHUB_TOKEN }}
+          run: |
+            ''${{ github.head_ref && format('gh pr checkout {0}', github.event.pull_request.number) || ${"''"}}}
+
+            git config --global user.name "github-actions[bot]"
+            git config --global user.email "github-actions[bot]@users.noreply.github.com"
+
+        - name: Rebase
+          run: ''${{ env.git_pull }}
+
+        - name: Install packages & Build the action
+          run: nix run .#install
+
+        - name: Update docs
+          run: nix run .#write
+
+        - name: Commit & push changes
+          run: |
+            git add dist
+            git commit -m "chore: build the action" || echo "Nothing to commit"
+            git add .
+            git commit -m "chore: update docs" || echo "Nothing to commit"
+            git push
+
+    # Make `individual` caches
+    # Restore `individual` or `common` caches
+    # Usually, there should be no `individual` caches to restore as they're purged by `merge-similar-caches`
+    make-similar-caches:
+      name: Make similar caches
+      needs: build
+      permissions:
+        actions: write
+      strategy:
+        matrix:
+          os:
+            - macos-11
+            - macos-12
+            - ubuntu-20.04
+            - ubuntu-22.04
+          id:
+            - 1
+            - 2
+      runs-on: ''${{ matrix.os }}
+      steps:
+        - name: Checkout this repo
+          uses: actions/checkout@v4
+
+        - name: Rebase
+          run: ''${{ env.git_pull }}
+
+        - uses: nixbuild/nix-quick-install-action@v27
+
+        - name: Restore and save Nix store - ''${{ matrix.id }}
+          uses: ./.
+          with:
+            # save a new cache every time `ci.yaml` changes
+            primary-key: similar-cache-''${{ matrix.os }}-individual-''${{ matrix.id }}-''${{ hashFiles('.github/workflows/ci.yaml') }}
+            # otherwise, restore a common cache if and only if it matches the current `ci.yaml`
+            restore-prefixes-first-match: similar-cache-''${{ matrix.os }}-common-''${{ hashFiles('.github/workflows/ci.yaml') }}
+            # do purge caches
+            purge: true
+            # purge all versions of the cache
+            purge-prefixes: similar-cache-''${{ matrix.os }}-individual-''${{ matrix.id }}-
+            # created more than 0 seconds ago relative to the start of the `Post Restore` phase
+            purge-created: 0
+            # except the version with the `primary-key`, if it exists
+            purge-primary-key: never
+            ${backend_}
+
+        - name: Pin nixpkgs
+          run: ''${{ env.pin_nixpkgs }}
+
+        - name: Install nixpkgs#poetry
+          if: ''${{ matrix.id == 1 }}
+          run: nix profile install nixpkgs#poetry
+
+        - name: Install nixpkgs#nodejs
+          if: ''${{ matrix.id == 2 }}
+          run: nix profile install nixpkgs#nodejs
+
+    # Merge similar `individual` caches
+    # Purge `individual` caches and old `common` caches
+    # Save new `common` caches
+    merge-similar-caches:
+      name: Merge similar caches
+      needs: make-similar-caches
+      permissions:
+        actions: write
+      strategy:
+        matrix:
+          os:
+            - macos-11
+            - macos-12
+            - ubuntu-20.04
+            - ubuntu-22.04
+      runs-on: ''${{ matrix.os }}
+      steps:
+        - name: Checkout this repo
+          uses: actions/checkout@v4
+
+        - name: Rebase
+          run: ''${{ env.git_pull }}
+
+        - uses: nixbuild/nix-quick-install-action@v27
+
+        - name: Restore and save Nix store
+          uses: ./.
+          with:
+            primary-key: similar-cache-''${{ matrix.os }}-common-''${{ hashFiles('.github/workflows/ci.yaml') }}
+            # when there's a common cache hit, don't restore individual caches
+            skip-restore-on-hit-primary-key: true
+            # otherwise, restore individual caches, but not their old versions
+            restore-prefixes-all-matches: |
+              similar-cache-''${{ matrix.os }}-individual-1-''${{ hashFiles('.github/workflows/ci.yaml') }}
+              similar-cache-''${{ matrix.os }}-individual-2-''${{ hashFiles('.github/workflows/ci.yaml') }}
+            # do purge caches
+            purge: true
+            # purge all versions of the cache
+            purge-prefixes: similar-cache-''${{ matrix.os }}-common-
+            # created more than 0 seconds ago relative to the start of the `Post Restore` phase
+            purge-created: 0
+            # except the version with the `primary-key`, if it exists
+            purge-primary-key: never
+            ${backend_}
+
+        - name: Pin nixpkgs
+          run: ''${{ env.pin_nixpkgs }}
+
+        # Stuff in a profile can survive garbage collection.
+        # Therefore, profiles are ignored when restoring a cache.
+        # So, the current profile should be the default profile created by nix-quick-install-action.
+        # The default profile should contain only nix.
+        - name: List profile (should be empty)
+          run: nix profile list
+
+        - name: Check that the profile is empty
+          shell: bash
+          run: |
+            nix profile list \
+            | grep 'Index' \
+            | wc -l \
+            | xargs test 1 -eq
+
+        - name: Install nixpkgs#poetry
+          run: nix profile install nixpkgs#poetry
+
+        - name: Install nixpkgs#nodejs
+          run: nix profile install nixpkgs#nodejs
+
+        - name: Run poetry
+          run: poetry --version
+
+        - name: Run node
+          run: node --version
+
+    compare-run-times:
+      name: Job with caching
+      needs: merge-similar-caches
+      permissions:
+        actions: write
+      strategy:
+        matrix:
+          do-cache:
+            - true
+            - false
+          os:
+            - macos-11
+            - macos-12
+            - ubuntu-20.04
+            - ubuntu-22.04
+      runs-on: ''${{ matrix.os }}
+      steps:
+        - name: Checkout this repo
+          uses: actions/checkout@v4
+
+        - name: Rebase
+          run: ''${{ env.git_pull }}
+
+        - uses: nixbuild/nix-quick-install-action@v27
+
+        - name: Restore and save Nix store
+          if: ''${{ matrix.do-cache }}
+          uses: ./.
+          with:
+            # save a new cache every time ci file changes
+            primary-key: cache-''${{ matrix.os }}-''${{ hashFiles('.github/workflows/ci.yaml') }}
+            restore-prefixes-first-match: cache-''${{ matrix.os }}-
+            # do purge caches
+            purge: true
+            # purge all versions of the cache
+            purge-prefixes: cache-''${{ matrix.os }}-
+            # created more than 0 seconds ago relative to the start of the `Post Restore` phase
+            purge-created: 0
+            # except the version with the `primary-key`, if it exists
+            purge-primary-key: never
+            # and collect garbage in the Nix store until it reaches this size in bytes
+            gc-max-store-size: 8000000000
+            ${backend_}
+
+        # Uncomment to debug this job
+        # - name: Setup tmate session
+        #   uses: mxschmitt/action-tmate@v3
+
+        - name: Show profile
+          run: nix profile list
+
+        - name: Pin nixpkgs
+          run: ''${{ env.pin_nixpkgs }}
+
+        - name: List registry
+          run: nix registry list
+
+        - name: Install nixpkgs
+          run: nix profile install $(nix flake archive nixpkgs --json | jq -r '.path')
+
+        - name: Show profile
+          run: nix profile list
+
+        - name: Install nixpkgs#hello
+          run: |
+            nix profile install nixpkgs#hello
+
+        - name: Install nixpkgs#cachix
+          run: |
+            nix profile install nixpkgs#cachix
+
+        - name: Install nixpkgs#nixpkgs-fmt
+          run: |
+            nix profile install nixpkgs#nixpkgs-fmt
+
+        - name: Install nixpkgs#alejandra
+          run: |
+            nix profile install nixpkgs#alejandra
+
+        - name: Install nixpkgs#nixd
+          run: |
+            nix profile install nixpkgs#nixd
+
+        - name: Install nixpkgs#ghc
+          run: |
+            nix profile install nixpkgs#ghc
+
+        - name: Install nixpkgs#haskell-language-server
+          run: |
+            nix profile install nixpkgs#haskell-language-server
+
+        - name: Install nixpkgs#purescript
+          run: |
+            nix profile install nixpkgs#purescript
+
+        - name: Install nixpkgs#nodejs
+          run: |
+            nix profile install nixpkgs#nodejs
+
+        - name: Show profile
+          run: nix profile list
+''
diff --git a/package.json b/package.json
index 8fdd6683..ce0501d1 100644
--- a/package.json
+++ b/package.json
@@ -9,7 +9,8 @@
     "build": "MERGE=\"$(cat src/templates/merge.sql)\"; printf 'export const mergeSqlTemplate = `\n%s\n`' \"$MERGE\" > src/templates/merge.ts; tsc && ncc build -o dist/restore src/restore.ts && ncc build -o dist/save src/save.ts && ncc build -o dist/restore-only src/restoreOnly.ts && ncc build -o dist/save-only src/saveOnly.ts",
     "test": "tsc --noEmit && jest --coverage",
     "lint": "eslint **/*.ts --cache",
-    "format": "prettier --write **/*.ts .github/workflows/ci.yaml **/*.md",
+    "format": "prettier --write **/*.ts **/*.md **/action.yml",
+    "format-ci": "prettier --write .github/workflows/*.yaml",
     "format-check": "prettier --check **/*.ts",
     "readme": "npx action-docs -u; (cd save; npx action-docs -u); (cd restore; npx action-docs -u); prettier --write restore/README.md save/README.md README.md"
   },