diff --git a/.github/workflows/scheduled_sync.yml b/.github/workflows/scheduled_sync.yml
index 16716c3..5e3a44c 100644
--- a/.github/workflows/scheduled_sync.yml
+++ b/.github/workflows/scheduled_sync.yml
@@ -12,30 +12,13 @@ jobs:
       COVER_PDF_PATH: resources/cover.pdf
     steps:
       - uses: actions/checkout@v4
-      - name: setup python
-        uses: actions/setup-python@v4
-        with:
-          python-version: '3.11'
-          architecture: 'x64'
-      - name: install python dependencies
-        run: |
-          python -m pip install --upgrade pip
-          pip install -r requirements.txt
+      - uses: cachix/install-nix-action@v30
       - name: build pdf
-        run: python main_async.py
+        run: nix develop --command 'python main_async.py'
       - name: optimize pdf size
         run: |
-          mkdir pdfsizeopt
-          cd pdfsizeopt
-          wget -O pdfsizeopt_libexec_linux.tar.gz https://github.com/pts/pdfsizeopt/releases/download/2023-04-18/pdfsizeopt_libexec_linux-v9.tar.gz
-          tar xzvf pdfsizeopt_libexec_linux.tar.gz
-          rm -f    pdfsizeopt_libexec_linux.tar.gz
-          wget -O pdfsizeopt.single https://raw.githubusercontent.com/pts/pdfsizeopt/master/pdfsizeopt.single
-          chmod +x pdfsizeopt.single
-          ln -s pdfsizeopt.single pdfsizeopt
-          cd ..
           mv out/guide.pdf .
-          ./pdfsizeopt/pdfsizeopt guide.pdf out/guide.pdf
+          gs -sDEVICE=pdfwrite -dCompatibilityLevel=1.4 -dPDFSETTINGS=/prepress -dNOPAUSE -dQUIET -dBATCH -sOutputFile=out/guide.pdf guide.pdf
       - name: build redirect page
         run: cp resources/index.html out/index.html
       - name: upload
diff --git a/flake.lock b/flake.lock
new file mode 100644
index 0000000..0cfaf0b
--- /dev/null
+++ b/flake.lock
@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1733479337,
+        "narHash": "sha256-MQU+VnrN/L03J/Mq3apkpKUOIryWiDv41FWqNmIknu0=",
+        "owner": "yoctocell",
+        "repo": "nixpkgs",
+        "rev": "d1ae543c98eda497cf0724da2795fcfd3dac029e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "yoctocell",
+        "ref": "add-python-lark-oapi",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}
diff --git a/flake.nix b/flake.nix
new file mode 100644
index 0000000..2946327
--- /dev/null
+++ b/flake.nix
@@ -0,0 +1,24 @@
+{
+  description = "ACSSZ guide for new students and scholars";
+
+  # TODO 使用上游仓库
+  inputs.nixpkgs.url = "github:yoctocell/nixpkgs/add-python-lark-oapi";
+
+  outputs = { self, nixpkgs }:
+    let pkgs = nixpkgs.legacyPackages.x86_64-linux;
+    in with pkgs; {
+      devShell.x86_64-linux = mkShell {
+        name = "acssz-guide";
+        buildInputs = [
+          # For compressing pdfs, see <https://askubuntu.com/a/256449>
+          ghostscript
+          pkgs.python3Packages.pymupdf
+          (pkgs.python3.withPackages (pp: with pp; [
+            requests
+            websockets
+            lark-oapi
+          ]))
+        ];
+      };
+   };
+}