diff --git a/.gitignore b/.gitignore
index 629b351..1689399 100644
--- a/.gitignore
+++ b/.gitignore
@@ -12,6 +12,10 @@ storage/test.db
 error.log
 src/cache/rate_limit/
 
+# Nix
+.direnv/
+result
+
 # OS files
 .DS_Store
 Thumbs.db
diff --git a/TODO.md b/TODO.md
index 516e5c3..ceec361 100644
--- a/TODO.md
+++ b/TODO.md
@@ -35,6 +35,7 @@
 
 ## Pending
 
+- [x] Add flake.nix for Nix-based PHP dev environment
 - [x] Add favicon (`<link rel="icon">` → admin_favicon.svg) to all pages; nginx 204 for /favicon.ico
 - [ ] Add pagination to répertoire student index (currently capped at 100)
 - [ ] Thumbnail generation / cover image support for home grid cards
diff --git a/flake.nix b/flake.nix
new file mode 100644
index 0000000..ad1d2fa
--- /dev/null
+++ b/flake.nix
@@ -0,0 +1,49 @@
+{
+  description = "Post-ERG development environment";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+
+        php = pkgs.php84.buildEnv {
+          extensions = ({ enabled, all }: enabled ++ (with all; [
+            curl
+            mbstring
+            pdo
+            pdo_sqlite
+            sqlite3
+          ]));
+          extraConfig = ''
+            error_reporting = E_ALL
+            display_errors = On
+            log_errors = On
+          '';
+        };
+      in
+      {
+        devShells.default = pkgs.mkShell {
+          name = "posterg";
+
+          packages = [
+            php
+            pkgs.sqlite
+            pkgs.just
+            pkgs.git
+          ];
+
+          shellHook = ''
+            echo "🛠  Post-ERG dev shell"
+            echo "  php   $(php --version | head -1)"
+            echo "  just  $(just --version)"
+            echo ""
+            echo "Run 'just serve' to start the dev server."
+          '';
+        };
+      });
+}