diff --git a/.gitignore b/.gitignore
index 33d4929..53a29e3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,6 @@
 coverage/
 node_modules/
 .DS_Store
+*.d.ts
 *.log
 yarn.lock
diff --git a/index.js b/index.js
index d9b07fc..3e93d5a 100644
--- a/index.js
+++ b/index.js
@@ -1,51 +1,104 @@
+/**
+ * @typedef {import('mdast').Root} MdastRoot
+ * @typedef {import('hast').Root} HastRoot
+ * @typedef {import('hast').Element} HastElement
+ * @typedef {HastRoot|HastRoot['children'][number]} HastNode
+ * @typedef {import('virtual-dom').VNode} VNode
+ * @typedef {import('virtual-dom').VChild} VChild
+ * @typedef {import('virtual-dom').h} H
+ * @typedef {import('hast-util-sanitize').Schema} Schema
+ *
+ * @callback Component
+ * @param {string} name
+ * @param {Record<string, unknown>} props
+ * @param {VNode[]} children
+ * @returns {VNode|VNode[]}
+ *
+ * @typedef Options
+ *   Configuration.
+ * @property {boolean|Schema|null|undefined} [sanitize]
+ *   How to sanitize the output.
+ *
+ *   Sanitation is done by `hast-util-sanitize`, except when `false` is
+ *   given.
+ *   If an object is passed in, it’s given as a schema to `sanitize`.
+ *   By default, input is sanitized according to GitHub’s sanitation rules.
+ *
+ *   Embedded HTML is **always** stripped.
+ * @property {string|null|undefined} [prefix='h-']
+ *   Optimization hint.
+ * @property {H|null|undefined} [h]
+ *   Hyperscript to use.
+ * @property {Record<string, Component>} [components={}]
+ *   Map of tag names to custom components.
+ *   That component is invoked with `tagName`, `props`, and `children`.
+ *   It can return any VDOM compatible value (such as `VNode`, `VText`,
+ *   `Widget`).
+ */
+
 import {toHast} from 'mdast-util-to-hast'
 import {sanitize} from 'hast-util-sanitize'
 import {toH} from 'hast-to-hyperscript'
-import hyperscript from 'virtual-dom/h.js'
+import {h as defaultH} from 'virtual-dom'
 
 const own = {}.hasOwnProperty
 
-// Attach a VDOM compiler.
-export default function remarkVdom(options) {
-  const settings = options || {}
-  const info = settings.sanitize
+/**
+ * Plugin to compile Markdown to Virtual DOM.
+ *
+ * @type {import('unified').Plugin<[Options?]|void[], MdastRoot, VNode>}
+ */
+export default function remarkVdom(options = {}) {
+  const info = options.sanitize
   const clean = info !== false
   const schema = info && typeof info === 'object' ? info : null
-  const components = settings.components || {}
-  const h = settings.h || hyperscript
+  const components = options.components || {}
+  const h = options.h || defaultH
 
-  this.Compiler = compiler
+  Object.assign(this, {Compiler: compiler})
 
-  // Compile mdast to vdom.
+  /** @type {import('unified').CompilerFunction<MdastRoot, VNode>} */
   function compiler(node) {
+    /** @type {HastNode} */
+    // @ts-expect-error: assume a root w/o doctypes.
     let hast = div(toHast(node).children)
 
     if (clean) {
-      hast = sanitize(hast, schema)
+      hast = sanitize(hast, schema || undefined)
 
       // If `div` is removed by sanitation, add it back.
       if (hast.type === 'root') {
+        // @ts-expect-error: assume a root w/o doctypes.
         hast = div(hast.children)
       }
     }
 
-    return toH(w, hast, settings.prefix)
+    // @ts-expect-error: assume no doctypes.
+    return toH(w, hast, options.prefix)
   }
 
-  // Wrapper around `h` to pass components in.
+  /**
+   * Wrapper around `h` to pass components in.
+   *
+   * @param {string} name
+   * @param {object} props
+   * @param {VChild[]|undefined} children
+   * @returns {VNode|VNode[]}
+   */
   function w(name, props, children) {
     const id = name.toLowerCase()
     const fn = own.call(components, id) ? components[id] : h
-    return fn(name, props, children)
+    // @ts-expect-error: vdom types vague.
+    return fn(name, props, children || [])
   }
 
-  // Wrap `children` in a hast div.
+  /**
+   * Wrap `children` in a hast div.
+   *
+   * @param {HastElement['children']} children
+   * @returns {HastElement}
+   */
   function div(children) {
-    return {
-      type: 'element',
-      tagName: 'div',
-      properties: {},
-      children
-    }
+    return {type: 'element', tagName: 'div', properties: {}, children}
   }
 }
diff --git a/package.json b/package.json
index dfac17c..daba41a 100644
--- a/package.json
+++ b/package.json
@@ -31,30 +31,41 @@
   "sideEffects": false,
   "type": "module",
   "main": "index.js",
+  "types": "index.d.ts",
   "files": [
+    "index.d.ts",
     "index.js"
   ],
   "dependencies": {
+    "@types/hast": "^2.3.2",
+    "@types/mdast": "^3.0.0",
     "hast-to-hyperscript": "^10.0.0",
     "hast-util-sanitize": "^4.0.0",
     "mdast-util-to-hast": "^11.0.0",
+    "unified": "^10.0.0",
     "virtual-dom": "^2.0.0"
   },
   "devDependencies": {
+    "@types/tape": "^4.0.0",
+    "@types/virtual-dom": "^2.1.1",
     "c8": "^7.0.0",
     "prettier": "^2.0.0",
     "remark": "^14.0.0",
     "remark-cli": "^10.0.0",
     "remark-preset-wooorm": "^8.0.0",
+    "rimraf": "^3.0.0",
     "tape": "^5.0.0",
+    "type-coverage": "^2.0.0",
+    "typescript": "^4.0.0",
     "vdom-to-html": "^2.0.0",
     "xo": "^0.39.0"
   },
   "scripts": {
+    "build": "rimraf \"*.d.ts\" && tsc && type-coverage",
     "format": "remark . -qfo && prettier . -w --loglevel warn && xo --fix",
     "test-api": "node --conditions development test.js",
     "test-coverage": "c8 --check-coverage --branches 100 --functions 100 --lines 100 --statements 100 --reporter lcov npm run test-api",
-    "test": "npm run format && npm run test-coverage"
+    "test": "npm run build && npm run format && npm run test-coverage"
   },
   "prettier": {
     "tabWidth": 2,
@@ -71,5 +82,11 @@
     "plugins": [
       "preset-wooorm"
     ]
+  },
+  "typeCoverage": {
+    "atLeast": 100,
+    "detail": true,
+    "strict": true,
+    "ignoreCatch": true
   }
 }
diff --git a/test.js b/test.js
index 28fcc49..af5f50a 100644
--- a/test.js
+++ b/test.js
@@ -1,10 +1,20 @@
+/**
+ * @typedef {import('./index.js').Options} Options
+ * @typedef {import('virtual-dom').VNode} VNode
+ */
+
 import test from 'tape'
 import {remark} from 'remark'
-import h from 'virtual-dom/h.js'
+import {h} from 'virtual-dom'
+// @ts-expect-error: untyped.
 import vdom2html from 'vdom-to-html'
 import vdom from './index.js'
 
 test('remark-vdom', (t) => {
+  /**
+   * @param {string} [fixture]
+   * @param {Options} [options]
+   */
   function check(fixture, options) {
     return vdom2html(remark().use(vdom, options).processSync(fixture).result)
   }
@@ -23,6 +33,7 @@ test('remark-vdom', (t) => {
 
   t.equal(
     check('_Emphasis_!', {
+      // @ts-expect-error: TS tripping up, it’s fine.
       h(name, props, children) {
         return h(name === 'EM' ? 'I' : name, props, children)
       }
@@ -50,7 +61,7 @@ test('remark-vdom', (t) => {
   t.equal(
     check('_Emphasis_!', {
       components: {
-        em(name, props, children) {
+        em(_, _1, children) {
           return children
         }
       }
@@ -59,9 +70,9 @@ test('remark-vdom', (t) => {
     '`components`'
   )
 
-  const node = remark()
-    .use(vdom, {prefix: 'f-'})
-    .processSync('_Emphasis_!').result
+  const node = /** @type {VNode} */ (
+    remark().use(vdom, {prefix: 'f-'}).processSync('_Emphasis_!').result
+  )
 
   t.equal(node.key, 'f-1', '`prefix`')
 
diff --git a/tsconfig.json b/tsconfig.json
new file mode 100644
index 0000000..e31adf8
--- /dev/null
+++ b/tsconfig.json
@@ -0,0 +1,16 @@
+{
+  "include": ["*.js"],
+  "compilerOptions": {
+    "target": "ES2020",
+    "lib": ["ES2020"],
+    "module": "ES2020",
+    "moduleResolution": "node",
+    "allowJs": true,
+    "checkJs": true,
+    "declaration": true,
+    "emitDeclarationOnly": true,
+    "allowSyntheticDefaultImports": true,
+    "skipLibCheck": true,
+    "strict": true
+  }
+}