diff --git a/.gitignore b/.gitignore
index d9d5ed5..3407d14 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,4 @@
 dist/
 node_modules/
 scratch/
+types/
diff --git a/package.json b/package.json
index a0487d4..2571773 100644
--- a/package.json
+++ b/package.json
@@ -50,7 +50,8 @@
     "module-alias": "2",
     "rollup": "2",
     "rollup-plugin-terser": "7",
-    "snowpack": "3"
+    "snowpack": "3",
+    "typescript": "^4.8.3"
   },
   "dependencies": {
     "htl": "0.3",
diff --git a/src/range.js b/src/range.js
index d129fe8..6e3d181 100644
--- a/src/range.js
+++ b/src/range.js
@@ -13,10 +13,43 @@ export function number(extent, options) {
   return createRange({extent}, options);
 }
 
+/**
+ * @typedef {{ label: string, step: number, format: (d: number) => string,
+ *   placeholder: string, transform: (d: number) => number, invert: (d: number)
+ *   => number, validate: (d: number) => boolean, value: number, width: number,
+ *   disabled: boolean }} Options
+ */
+
+/**
+ * A Range input specifies a number between the given *extent* = [*min*, *max*]
+ * (inclusive). If an *extent* is not specified, it defaults to [0, 1]. The
+ * chosen number can be adjusted roughly with a slider, or precisely by typing a
+ * number.
+ *
+ * The available *options* are:
+ *
+ * * *label* - a label; either a string or an HTML element.
+ * * *step* - the step (precision); the interval between adjacent values.
+ * * *format* - a format function; defaults to [formatTrim](#formatTrim).
+ * * *placeholder* - a placeholder string for when the input is empty.
+ * * *transform* - an optional non-linear transform.
+ * * *invert* - the inverse transform.
+ * * *validate* - a function to check whether the number input is valid.
+ * * *value* - the initial value; defaults to (*min* + *max*) / 2.
+ * * *width* - the width of the input (not including the label).
+ * * *disabled* - whether input is disabled; defaults to false.
+ *
+ * @param {[number, number]} extent
+ * @param {Options} options
+ * @returns Element
+ */
 export function range(extent = [0, 1], options) {
   return createRange({extent, range: true}, options);
 }
 
+/**
+ * @returns Element
+ */
 function createRange({
   extent: [min, max],
   range
diff --git a/tsconfig.json b/tsconfig.json
new file mode 100644
index 0000000..55ff635
--- /dev/null
+++ b/tsconfig.json
@@ -0,0 +1,19 @@
+{
+  "compilerOptions": {
+    "target": "esnext",
+    "module": "esnext",
+    "lib": ["esnext", "dom"],
+    "strict": true,
+    "stripInternal": true,
+    "outDir": "dist",
+    "allowJs": true,
+    "declaration": true,
+    "declarationDir": "types",
+    "resolveJsonModule": true,
+    "moduleResolution": "node",
+    "paths": {
+      "@observablehq/inputs": ["./src/index.js"]
+    }
+  },
+  "include": ["src/**/*"]
+}
diff --git a/yarn.lock b/yarn.lock
index 81cedfa..e5ca6ae 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -3857,6 +3857,11 @@ typedarray-to-buffer@^3.1.5:
   dependencies:
     is-typedarray "^1.0.0"
 
+typescript@^4.8.3:
+  version "4.8.3"
+  resolved "https://registry.npmjs.org/typescript/-/typescript-4.8.3.tgz#d59344522c4bc464a65a730ac695007fdb66dd88"
+  integrity sha512-goMHfm00nWPa8UvR/CPSvykqf6dVV8x/dp0c5mFTMTIu0u0FlGWRioyy7Nn0PGAdHxpJZnuO/ut+PpQ8UiHAig==
+
 unique-filename@^1.1.1:
   version "1.1.1"
   resolved "https://registry.yarnpkg.com/unique-filename/-/unique-filename-1.1.1.tgz#1d69769369ada0583103a1e6ae87681b56573230"