diff --git a/.changeset/ts-last-modified.md b/.changeset/ts-last-modified.md
new file mode 100644
index 0000000..82a4091
--- /dev/null
+++ b/.changeset/ts-last-modified.md
@@ -0,0 +1,5 @@
+---
+'markdown-magic-last-modified': minor
+---
+
+TypeScript: ship type declarations
diff --git a/packages/last-modified/README.md b/packages/last-modified/README.md
index b605c8a..d3d6f10 100644
--- a/packages/last-modified/README.md
+++ b/packages/last-modified/README.md
@@ -10,14 +10,14 @@ npm i markdown-magic markdown-magic-last-modified --save-dev
 
 ## Adding the plugin
 
-See `example.js` for usage.
+See `example.ts` for usage.
 
-<!-- AUTO-GENERATED-CONTENT:START (CODE:src=./example.js) -->
+<!-- AUTO-GENERATED-CONTENT:START (CODE:src=./example.ts) -->
 
-```js
+```ts
 import path from 'path';
 import { markdownMagic } from 'markdown-magic';
-import LASTMODIFIED from './index.js';
+import LASTMODIFIED from './index.ts';
 
 const config = {
   matchWord: 'AUTO-GENERATED-CONTENT',
diff --git a/packages/last-modified/example.js b/packages/last-modified/example.ts
similarity index 87%
rename from packages/last-modified/example.js
rename to packages/last-modified/example.ts
index 86e130a..2c7ad01 100644
--- a/packages/last-modified/example.js
+++ b/packages/last-modified/example.ts
@@ -1,6 +1,6 @@
 import path from 'path';
 import { markdownMagic } from 'markdown-magic';
-import LASTMODIFIED from './index.js';
+import LASTMODIFIED from './index.ts';
 
 const config = {
   matchWord: 'AUTO-GENERATED-CONTENT',
diff --git a/packages/last-modified/index.spec.js b/packages/last-modified/index.spec.ts
similarity index 96%
rename from packages/last-modified/index.spec.js
rename to packages/last-modified/index.spec.ts
index 7d41ab2..46bd709 100644
--- a/packages/last-modified/index.spec.js
+++ b/packages/last-modified/index.spec.ts
@@ -1,7 +1,7 @@
 import { mkdirSync, rmSync, writeFileSync } from 'fs';
 import path from 'path';
 import { describe, expect, it } from 'vitest';
-import format from './index.js';
+import format from './index.ts';
 
 const srcPath = path.join(import.meta.dirname, 'README.md');
 
diff --git a/packages/last-modified/index.js b/packages/last-modified/index.ts
similarity index 71%
rename from packages/last-modified/index.js
rename to packages/last-modified/index.ts
index 297d6f9..92b698d 100644
--- a/packages/last-modified/index.js
+++ b/packages/last-modified/index.ts
@@ -1,8 +1,15 @@
-import path from 'path';
 import { execFileSync } from 'child_process';
+import path from 'path';
+import type { TransformArgs } from './types.ts';
+
+export type { TransformArgs, TransformOptions } from './types.ts';
 
-export default function LASTMODIFIED({ content, options = {}, srcPath }) {
-  let filePath;
+export default function LASTMODIFIED({
+  content,
+  options = {},
+  srcPath,
+}: TransformArgs): string {
+  let filePath: string;
 
   if (options.file) {
     filePath = path.resolve(path.dirname(srcPath), options.file);
diff --git a/packages/last-modified/package.json b/packages/last-modified/package.json
index 5750a9f..cbeaba3 100644
--- a/packages/last-modified/package.json
+++ b/packages/last-modified/package.json
@@ -3,17 +3,21 @@
   "version": "2.0.0",
   "description": "Print the last modified date using git for a given file",
   "type": "module",
-  "main": "index.js",
+  "main": "dist/index.js",
+  "types": "dist/index.d.ts",
   "exports": {
-    ".": "./index.js",
+    ".": "./dist/index.js",
     "./package.json": "./package.json"
   },
   "engines": {
     "node": ">=22.18.0"
   },
   "scripts": {
+    "prebuild": "rm -rf dist",
+    "build": "tsc --project tsconfig.build.json",
+    "prepack": "pnpm build",
     "test": "vitest run",
-    "docs": "node example.js && prettier --write README.md",
+    "docs": "node example.ts && prettier --write README.md",
     "format": "prettier --write ."
   },
   "license": "MIT",
@@ -32,8 +36,10 @@
     "markdown-magic": "^4"
   },
   "devDependencies": {
+    "@types/node": "^24.13.2",
     "markdown-magic": "catalog:",
     "prettier": "catalog:",
+    "typescript": "^6.0.3",
     "vitest": "catalog:"
   },
   "homepage": "https://github.com/camacho/markdown-magic-plugins#readme",
@@ -41,6 +47,6 @@
     "url": "https://github.com/camacho/markdown-magic-plugins/issues"
   },
   "files": [
-    "index.js"
+    "dist"
   ]
 }
diff --git a/packages/last-modified/tsconfig.build.json b/packages/last-modified/tsconfig.build.json
new file mode 100644
index 0000000..d7ec333
--- /dev/null
+++ b/packages/last-modified/tsconfig.build.json
@@ -0,0 +1,18 @@
+{
+  "extends": "../../tsconfig.json",
+  "compilerOptions": {
+    "noEmit": false,
+    "outDir": "dist",
+    "rootDir": ".",
+    "types": ["node"]
+  },
+  "exclude": [
+    "node_modules",
+    "dist",
+    "*.spec.ts",
+    "example.ts",
+    "__fixtures__",
+    "__snapshots__"
+  ],
+  "include": ["*.ts"]
+}
diff --git a/packages/last-modified/types.ts b/packages/last-modified/types.ts
new file mode 100644
index 0000000..64c1458
--- /dev/null
+++ b/packages/last-modified/types.ts
@@ -0,0 +1,14 @@
+// Transform interface shared by markdown-magic plugins. Adapted from
+// format-package's scripts/markdown-transformers.ts TransformArgs/TransformOptions
+// (content: unknown -> content: string, the plugins' actual contract), plus
+// this package's own `file` option.
+export interface TransformOptions {
+  file?: string;
+  [key: string]: unknown;
+}
+
+export interface TransformArgs {
+  content: string;
+  options: TransformOptions;
+  srcPath: string;
+}
diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index 12eb245..181f5c5 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -160,12 +160,18 @@ importers:
 
   packages/last-modified:
     devDependencies:
+      '@types/node':
+        specifier: ^24.13.2
+        version: 24.13.2
       markdown-magic:
         specifier: 'catalog:'
         version: 4.10.5
       prettier:
         specifier: 'catalog:'
         version: 3.9.1
+      typescript:
+        specifier: ^6.0.3
+        version: 6.0.3
       vitest:
         specifier: 'catalog:'
         version: 4.1.9(@types/node@24.13.2)(vite@8.1.0(@types/node@24.13.2))