diff --git a/.github/workflows/nix.yml b/.github/workflows/nix.yml
index 4f569c360..6463e0bb4 100644
--- a/.github/workflows/nix.yml
+++ b/.github/workflows/nix.yml
@@ -131,7 +131,6 @@ jobs:
         run: |
           nix build -L --no-link \
             .#checks.${{ matrix.system }}.smoke \
-            .#checks.${{ matrix.system }}.formatting \
             .#checks.${{ matrix.system }}.repo-hygiene
 
       - name: Smoke-test
diff --git a/README.md b/README.md
index 8921dfaf1..93184c10f 100644
--- a/README.md
+++ b/README.md
@@ -110,18 +110,6 @@ npm run check         # Lint, format, and type check
 ./pi-test.sh         # Run pi from sources (can be run from any directory)
 ```
 
-### Nix development shell
-
-The flake provides the same toolchain without npm-managed binaries. Node.js 22
-and the Biome version pinned in `package.json` come from Nix, so `nix fmt` and
-`npm run check` format the same way.
-
-```bash
-nix develop           # Shell with Node.js, Biome, and treefmt
-nix fmt               # Format JavaScript, TypeScript, JSON, CSS, and Nix
-nix flake check       # Build pi, then run the smoke, formatting, and hygiene checks
-```
-
 ### Using local packages outside the monorepo
 
 Build every public package into one coherent local artifact set:
diff --git a/flake.nix b/flake.nix
index 6de98a81e..61c780f97 100644
--- a/flake.nix
+++ b/flake.nix
@@ -36,9 +36,6 @@
       forAllSystems = genAttrs platforms;
 
       piOverlay = _final: prev: {
-        biome = prev.callPackage ./nix/biome.nix {
-          inherit source;
-        };
         pi = prev.callPackage ./nix/package.nix {
           inherit source packageJson platforms;
           nodejs = prev.nodejs_22;
@@ -49,19 +46,11 @@
         system:
         let
           pkgs = (nixpkgsFor system).extend piOverlay;
-          inherit (pkgs) pi;
-          nodejs = pkgs.nodejs_22;
-          treefmtWrapper = import ./nix/treefmt.nix { inherit pkgs; };
-          devShell = import ./nix/devshell.nix { inherit pkgs nodejs treefmtWrapper; };
         in
         {
-          inherit
-            pkgs
-            pi
-            nodejs
-            devShell
-            treefmtWrapper
-            ;
+          inherit pkgs;
+          inherit (pkgs) pi;
+          nodejs = pkgs.nodejs_22;
         }
       );
     in
@@ -69,12 +58,7 @@
       checks = forAllSystems (
         system:
         import ./nix/checks.nix {
-          inherit (perSystem.${system})
-            pkgs
-            pi
-            nodejs
-            treefmtWrapper
-            ;
+          inherit (perSystem.${system}) pkgs pi nodejs;
           inherit source;
         }
       );
@@ -84,12 +68,6 @@
         pi = perSystem.${system}.pi;
       });
 
-      devShells = forAllSystems (system: {
-        default = perSystem.${system}.devShell;
-      });
-
-      formatter = forAllSystems (system: perSystem.${system}.treefmtWrapper);
-
       apps = forAllSystems (system: rec {
         default = pi;
         pi = {
diff --git a/nix/biome.nix b/nix/biome.nix
deleted file mode 100644
index 22514ff2c..000000000
--- a/nix/biome.nix
+++ /dev/null
@@ -1,54 +0,0 @@
-{
-  lib,
-  stdenv,
-  fetchurl,
-  autoPatchelfHook,
-  source,
-}:
-let
-  inherit (lib) importJSON optionals licenses;
-in
-stdenv.mkDerivation (finalAttrs: {
-  pname = "biome";
-  version = (importJSON "${source}/package.json").devDependencies."@biomejs/biome";
-
-  src =
-    finalAttrs.passthru.sources.${stdenv.hostPlatform.system}
-      or (throw "Unsupported system for Biome: ${stdenv.hostPlatform.system}");
-
-  nativeBuildInputs = optionals stdenv.hostPlatform.isLinux [ autoPatchelfHook ];
-  buildInputs = optionals stdenv.hostPlatform.isLinux [ stdenv.cc.cc.lib ];
-
-  installPhase = ''
-    runHook preInstall
-    install -Dm755 biome $out/bin/biome
-    runHook postInstall
-  '';
-
-  passthru.sources = {
-    x86_64-linux = fetchurl {
-      url = "https://registry.npmjs.org/@biomejs/cli-linux-x64/-/cli-linux-x64-${finalAttrs.version}.tgz";
-      hash = "sha256-2k7rG5YgEyMtJ7jAI+JWPzWhdxlNZI6TqyMVngU9Dus=";
-    };
-    aarch64-linux = fetchurl {
-      url = "https://registry.npmjs.org/@biomejs/cli-linux-arm64/-/cli-linux-arm64-${finalAttrs.version}.tgz";
-      hash = "sha256-cLKXQ7uIyS2aQ7P95IHh7A7hI7z89p8WUKeYW3/4N/I=";
-    };
-    x86_64-darwin = fetchurl {
-      url = "https://registry.npmjs.org/@biomejs/cli-darwin-x64/-/cli-darwin-x64-${finalAttrs.version}.tgz";
-      hash = "sha256-cD7JJVxSXEAQnYSgWAbOC1EPJ+M0+q7h0xg57OXao4o=";
-    };
-    aarch64-darwin = fetchurl {
-      url = "https://registry.npmjs.org/@biomejs/cli-darwin-arm64/-/cli-darwin-arm64-${finalAttrs.version}.tgz";
-      hash = "sha256-sMi2Aywy3UnD9hQPyroTMPfCsFSZKRqqnb8uC5oNX34=";
-    };
-  };
-
-  meta = {
-    description = "Toolchain of the web";
-    homepage = "https://biomejs.dev/";
-    license = licenses.mit;
-    platforms = builtins.attrNames finalAttrs.passthru.sources;
-    mainProgram = finalAttrs.pname;
-  };
-})
diff --git a/nix/checks.nix b/nix/checks.nix
index f6a4d7099..ea640787a 100644
--- a/nix/checks.nix
+++ b/nix/checks.nix
@@ -1,7 +1,6 @@
 {
   pkgs,
   pi,
-  treefmtWrapper,
   source,
   nodejs,
 }:
@@ -18,27 +17,6 @@
         touch $out
       '';
 
-  formatting =
-    pkgs.runCommand "pi-formatting-check"
-      {
-        nativeBuildInputs = [
-          treefmtWrapper
-          pkgs.git
-        ];
-      }
-      ''
-        export HOME=$(mktemp -d)
-        mkdir repo && cd repo
-        cp -r ${source}/. .
-        chmod -R +w .
-        git init -q
-        git config user.email "test@example.com"
-        git config user.name "Test"
-        git add .
-        treefmt --ci
-        touch $out
-      '';
-
   repo-hygiene =
     pkgs.runCommand "pi-repo-hygiene-check"
       {
diff --git a/nix/devshell.nix b/nix/devshell.nix
deleted file mode 100644
index 7c3ea80f9..000000000
--- a/nix/devshell.nix
+++ /dev/null
@@ -1,21 +0,0 @@
-{
-  pkgs,
-  nodejs,
-  treefmtWrapper,
-}:
-let
-  inherit (pkgs.lib) getExe;
-in
-pkgs.mkShell {
-  packages = [
-    nodejs
-    pkgs.git
-    pkgs.biome
-    treefmtWrapper
-  ];
-
-  shellHook = ''
-    export BIOME_BINARY="${getExe pkgs.biome}"
-    git config core.hooksPath .husky
-  '';
-}
diff --git a/nix/treefmt.nix b/nix/treefmt.nix
deleted file mode 100644
index 7b51549cc..000000000
--- a/nix/treefmt.nix
+++ /dev/null
@@ -1,36 +0,0 @@
-{ pkgs }:
-pkgs.treefmt.withConfig {
-  runtimeInputs = with pkgs; [
-    biome
-    nixfmt
-  ];
-  settings = {
-    global.tree_root_file = "flake.nix";
-    formatter = {
-      biome = {
-        command = "biome";
-        options = [
-          "format"
-          "--write"
-          "--no-errors-on-unmatched"
-        ];
-        includes = [
-          "*.cjs"
-          "*.css"
-          "*.cts"
-          "*.graphql"
-          "*.js"
-          "*.json"
-          "*.jsonc"
-          "*.mjs"
-          "*.mts"
-          "*.ts"
-        ];
-      };
-      nixfmt = {
-        command = "nixfmt";
-        includes = [ "*.nix" ];
-      };
-    };
-  };
-}