diff --git a/README.md b/README.md
index f500718..b507cc5 100644
--- a/README.md
+++ b/README.md
@@ -37,7 +37,7 @@ Available via the [`json-sort` package][json-sort package], the binary is called
 
 ### Via the source code
 
-Clone the repository and run in the sourcecode folder:
+Clone the repository and run in the source code folder:
 
 ```sh
 cargo build --release
@@ -72,7 +72,7 @@ just serve
 Open <http://localhost:8080> and use the page to sort JSON object keys locally
 in the browser.
 
-Try the online demo on Github pages, find the link in the badge on top of this
+Try the online demo on GitHub Pages; the link is available in the badge at the top of this
 file.
 
 ### Via Nix
@@ -83,6 +83,33 @@ You can use the package from this repository with Nix. If you have Nix installed
 nix run github:drupol/json-sort
 ```
 
+### Treefmt module
+
+This repository also exposes a reusable `treefmtModule` as `treefmtModules.default`, so you can add the
+`json-sort` formatter to any `treefmt` configuration without duplicating the setup.
+
+```nix
+  treefmt = {
+    imports = [
+      inputs.json-sort.treefmtModules.default
+    ];
+    projectRootFile = "flake.nix";
+    programs = {
+      json-sort.enable = true;
+    };
+  };
+```
+
+Make sure to add the `json-sort` flake input:
+
+```nix
+  inputs = {
+    # ... 8< ...
+    json-sort.url = "github:drupol/json-sort";
+    # ... >8 ...
+  };
+```
+
 ## Usage
 
 ### Command Line
diff --git a/nix/modules/fmt.nix b/nix/modules/fmt.nix
index 530a1d8..a326519 100644
--- a/nix/modules/fmt.nix
+++ b/nix/modules/fmt.nix
@@ -1,12 +1,18 @@
 { inputs, ... }:
 {
-  imports = [ inputs.treefmt-nix.flakeModule ];
+  imports = [
+    inputs.treefmt-nix.flakeModule
+  ];
 
   perSystem = {
     treefmt = {
+      imports = [
+        inputs.self.treefmtModules.default
+      ];
       projectRootFile = "flake.nix";
       programs = {
         jsonfmt.enable = true;
+        json-sort.enable = true;
         nixfmt.enable = true;
         prettier.enable = true;
         statix.enable = true;
diff --git a/nix/modules/treefmt-module.nix b/nix/modules/treefmt-module.nix
new file mode 100644
index 0000000..b521b07
--- /dev/null
+++ b/nix/modules/treefmt-module.nix
@@ -0,0 +1,74 @@
+{
+  inputs,
+  ...
+}:
+let
+  treefmtModule =
+    {
+      lib,
+      config,
+      pkgs,
+      ...
+    }:
+    let
+      cfg = config.programs.json-sort;
+    in
+    {
+      config = lib.mkIf cfg.enable {
+        settings.formatter.json-sort = {
+          inherit (cfg) includes;
+          command = lib.getExe cfg.package;
+          options = [ "--fix" ];
+        }
+        // lib.optionalAttrs (cfg.excludes != [ ]) { inherit (cfg) excludes; }
+        // lib.optionalAttrs (cfg.priority != null) { inherit (cfg) priority; };
+      };
+      options.programs.json-sort = {
+        enable = lib.mkEnableOption "json-sort, the JSON formatter";
+        package = lib.mkOption {
+          default = pkgs.json-sort;
+          defaultText = lib.literalExpression "pedantix.packages.\${system}.pedantix-wrapped";
+          description = "The pedantix package to run. The default wrapper ships nixfmt, alejandra and nixpkgs-fmt on PATH; use the unwrapped `pedantix` package if you provide the base formatter yourself.";
+          type = lib.types.package;
+        };
+        excludes = lib.mkOption {
+          default = [ ];
+          description = "Path / file patterns to exclude.";
+          example = [ "generated/*.json" ];
+          type = lib.types.listOf lib.types.str;
+        };
+        includes = lib.mkOption {
+          default = [ "*.json" ];
+          description = "Path / file patterns to include.";
+          type = lib.types.listOf lib.types.str;
+        };
+        priority = lib.mkOption {
+          default = null;
+          description = "treefmt priority, for ordering relative to other formatters on the same files.";
+          type = lib.types.nullOr lib.types.int;
+        };
+      };
+    };
+in
+{
+  imports = [
+    inputs.flake-parts.flakeModules.flakeModules
+  ];
+
+  flake = {
+    flakeModules = {
+      default =
+        { flake-parts-lib, ... }:
+        {
+          options.perSystem = flake-parts-lib.mkPerSystemOption {
+            config.treefmt = {
+              imports = [ treefmtModule ];
+            };
+          };
+        };
+    };
+    treefmtModules = {
+      default = treefmtModule;
+    };
+  };
+}
diff --git a/web/index.html b/web/index.html
index 5db83f2..6436010 100644
--- a/web/index.html
+++ b/web/index.html
@@ -22,7 +22,8 @@ <h1 class="display-3 fw-bold mb-0">json-sort</h1>
             <span id="version" class="badge text-bg-secondary">v...</span>
           </div>
           <p class="lead text-body-secondary mb-0">
-            Sort JSON object keys in the browser with the Rust library compiled to WebAssembly.
+            Sort JSON object keys in the browser with the Rust library compiled
+            to WebAssembly.
           </p>
         </div>
         <div class="d-flex flex-wrap gap-2">
@@ -59,7 +60,11 @@ <h1 class="display-3 fw-bold mb-0">json-sort</h1>
               />
             </div>
             <div class="col-6">
-              <button id="random" class="btn btn-outline-primary btn-lg w-100" type="button">
+              <button
+                id="random"
+                class="btn btn-outline-primary btn-lg w-100"
+                type="button"
+              >
                 Generate a random JSON
               </button>
             </div>
@@ -75,16 +80,30 @@ <h1 class="display-3 fw-bold mb-0">json-sort</h1>
             readonly
           ></textarea>
           <div class="row g-2 mt-3">
-            <button id="sort" class="btn btn-primary btn-lg w-100" type="button">Sort JSON</button>
+            <button
+              id="sort"
+              class="btn btn-primary btn-lg w-100"
+              type="button"
+            >
+              Sort JSON
+            </button>
           </div>
         </div>
       </section>
 
-      <div id="status" class="alert mt-3 mb-0" role="status" aria-live="polite"></div>
+      <div
+        id="status"
+        class="alert mt-3 mb-0"
+        role="status"
+        aria-live="polite"
+      ></div>
     </main>
 
     <script type="module">
-      import init, { json_sort_version, sort_json_string } from "./pkg/json_sort.js";
+      import init, {
+        json_sort_version,
+        sort_json_string,
+      } from "./pkg/json_sort.js";
 
       const input = document.querySelector("#input");
       const output = document.querySelector("#output");
@@ -109,7 +128,9 @@ <h1 class="display-3 fw-bold mb-0">json-sort</h1>
           output.value = sort_json_string(input.value);
           setStatusOk("Sorted successfully.");
         } catch (error) {
-          setStatusError(error instanceof Error ? error.message : String(error));
+          setStatusError(
+            error instanceof Error ? error.message : String(error),
+          );
         }
       }
 
@@ -123,7 +144,9 @@ <h1 class="display-3 fw-bold mb-0">json-sort</h1>
 
       function randomKey() {
         const alphabet = "abcdefghijklmnopqrstuvwxyz";
-        return Array.from({ length: randomInteger(3, 12) }, () => randomItem(alphabet)).join("");
+        return Array.from({ length: randomInteger(3, 12) }, () =>
+          randomItem(alphabet),
+        ).join("");
       }
 
       function randomString() {
@@ -158,11 +181,16 @@ <h1 class="display-3 fw-bold mb-0">json-sort</h1>
         ];
 
         const nestedValues = [
-          () => Array.from({ length: randomInteger(2, 5) }, () => randomValue(depth + 1)),
+          () =>
+            Array.from({ length: randomInteger(2, 5) }, () =>
+              randomValue(depth + 1),
+            ),
           () => randomObject(depth + 1),
         ];
 
-        return randomItem(depth > 2 ? scalarValues : scalarValues.concat(nestedValues))();
+        return randomItem(
+          depth > 2 ? scalarValues : scalarValues.concat(nestedValues),
+        )();
       }
 
       function randomObject(depth = 0) {
@@ -210,7 +238,9 @@ <h1 class="display-3 fw-bold mb-0">json-sort</h1>
           sortInput();
           setStatusOk(`Loaded and sorted ${selectedFile.name}.`);
         } catch (error) {
-          setStatusError(error instanceof Error ? error.message : String(error));
+          setStatusError(
+            error instanceof Error ? error.message : String(error),
+          );
         }
       }