diff --git a/.tmux b/.tmux
index ed8e027..f7be89c 100755
--- a/.tmux
+++ b/.tmux
@@ -7,21 +7,18 @@ session_name="${1:-'build-configs'}"
 session_path="${2:-$(pwd)}"
 
 if tmux has-session -t="${session_name}" 2> /dev/null; then
-  tmux attach -t "${session_name}"
+  tmux switch-client -t "${session_name}" 2> /dev/null ||
+    tmux attach -t "${session_name}"
   exit
 fi
 
 tmux new-session -d -s "${session_name}" -n vim -c "${session_path}"
 
 # 1. Main window: Vim.
-tmux send-keys -t "${session_name}:vim" "nvim +GoToFile" Enter
+tmux send-keys -t "${session_name}:vim" "nvim" Enter
 
 # 2. General shell use.
 tmux new-window -t "${session_name}" -c "${session_path}"
 
-if [[ -n "${TMUX:-}" ]]; then
-  tmux switch-client -t "${session_name}"
-  tmux select-window -t "${session_name}:vim.left"
-else
+tmux switch-client -t "${session_name}:vim.left" ||
   tmux attach -t "${session_name}:vim.left"
-fi
diff --git a/build.yaml b/build.yaml
new file mode 100644
index 0000000..45ba308
--- /dev/null
+++ b/build.yaml
@@ -0,0 +1,9 @@
+name: build-configs
+type: symfony
+language: php
+
+flake:
+  devshell:
+    packages:
+      - php81
+      - php81Packages.composer
diff --git a/flake.lock b/flake.lock
index d824f37..6d62af8 100644
--- a/flake.lock
+++ b/flake.lock
@@ -1,5 +1,24 @@
 {
   "nodes": {
+    "devshell": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      },
+      "locked": {
+        "lastModified": 1705332421,
+        "narHash": "sha256-USpGLPme1IuqG78JNqSaRabilwkCyHmVWY0M9vYyqEA=",
+        "owner": "numtide",
+        "repo": "devshell",
+        "rev": "83cb93d6d063ad290beee669f4badf9914cc16ec",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "devshell",
+        "type": "github"
+      }
+    },
     "flake-parts": {
       "inputs": {
         "nixpkgs-lib": "nixpkgs-lib"
@@ -17,18 +36,36 @@
         "type": "indirect"
       }
     },
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1701680307,
+        "narHash": "sha256-kAuep2h5ajznlPMD9rnQyffWG8EM/C73lejGofXvdM8=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "4022d587cbbfd70fe950c1e2083a02621806a725",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1696374741,
-        "narHash": "sha256-gt8B3G0ryizT9HSB4cCO8QoxdbsHnrQH+/BdKxOwqF0=",
+        "lastModified": 1704161960,
+        "narHash": "sha256-QGua89Pmq+FBAro8NriTuoO/wNaUtugt29/qqA8zeeM=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "8a4c17493e5c39769f79117937c79e1c88de6729",
+        "rev": "63143ac2c9186be6d9da6035fa22620018c85932",
         "type": "github"
       },
       "original": {
         "owner": "NixOS",
-        "ref": "nixos-23.05",
+        "ref": "nixpkgs-unstable",
         "repo": "nixpkgs",
         "type": "github"
       }
@@ -51,10 +88,42 @@
         "type": "github"
       }
     },
+    "nixpkgs_2": {
+      "locked": {
+        "lastModified": 1705856552,
+        "narHash": "sha256-JXfnuEf5Yd6bhMs/uvM67/joxYKoysyE3M2k6T3eWbg=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "612f97239e2cc474c13c9dafa0df378058c5ad8d",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "root": {
       "inputs": {
+        "devshell": "devshell",
         "flake-parts": "flake-parts",
-        "nixpkgs": "nixpkgs"
+        "nixpkgs": "nixpkgs_2"
+      }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
       }
     }
   },
diff --git a/flake.nix b/flake.nix
index f0e0e11..a149852 100644
--- a/flake.nix
+++ b/flake.nix
@@ -1,19 +1,24 @@
+# Do not edit this file. It is automatically generated by https://www.oliverdavies.uk/build-configs.
+
 {
-  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-23.05";
+  inputs = {
+    devshell.url = "github:numtide/devshell";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+  };
 
   outputs = inputs@{ flake-parts, ... }:
     flake-parts.lib.mkFlake { inherit inputs; } {
+      imports = [ inputs.devshell.flakeModule ];
+
       systems = [ "x86_64-linux" ];
 
       perSystem = { config, self', inputs', pkgs, system, ... }: {
-        devShells.default = pkgs.mkShell {
-          buildInputs = with pkgs; [ php82 php82Packages.composer ];
+        devshells.default = {
+          packages = with pkgs; [
+            "php81"
+            "php81Packages.composer"
+          ];
         };
-
-        packages.default = pkgs.runCommand "default" { src = "./."; } ''
-          mkdir -p $out
-          cp ./build-configs $out
-        '';
       };
     };
 }