diff --git a/.gitignore b/.gitignore
index 735f4af..c977c85 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,5 @@
 .DS_Store
+*.d.ts
 *.log
 coverage/
 node_modules/
diff --git a/index.js b/index.js
index d111bc1..baa70d8 100644
--- a/index.js
+++ b/index.js
@@ -1,4 +1,9 @@
-// `collapse(' \t\nbar \nbaz\t') // ' bar baz '`
+/**
+ * Collapse whitespace to a single space.
+ *
+ * @param {string} value
+ * @returns {string}
+ */
 export function collapseWhiteSpace(value) {
   return String(value).replace(/\s+/g, ' ')
 }
diff --git a/package.json b/package.json
index 30f54b4..c597e3f 100644
--- a/package.json
+++ b/package.json
@@ -21,22 +21,30 @@
   "sideEffects": false,
   "type": "module",
   "main": "index.js",
+  "types": "index.d.ts",
   "files": [
+    "index.d.ts",
     "index.js"
   ],
   "devDependencies": {
+    "@types/tape": "^4.0.0",
     "c8": "^7.0.0",
     "prettier": "^2.0.0",
     "remark-cli": "^9.0.0",
     "remark-preset-wooorm": "^8.0.0",
+    "rimraf": "^3.0.0",
     "tape": "^5.0.0",
+    "typescript": "^4.0.0",
     "xo": "^0.38.0"
   },
   "scripts": {
+    "prepublishOnly": "npm run build",
     "format": "remark . -qfo && prettier . -w --loglevel warn && xo --fix",
+    "prebuild": "rimraf \"*.d.ts\"",
+    "build": "tsc",
     "test-api": "node test",
     "test-coverage": "c8 --check-coverage --branches 100 --functions 100 --lines 100 --statements 100 --reporter lcov node test.js",
-    "test": "npm run format && npm run test-coverage"
+    "test": "npm run format && npm run build && npm run test-coverage"
   },
   "prettier": {
     "tabWidth": 2,
diff --git a/readme.md b/readme.md
index 72bca33..e2600f0 100644
--- a/readme.md
+++ b/readme.md
@@ -33,7 +33,8 @@ There is no default export.
 
 ### `collapseWhiteSpace(value)`
 
-Replace multiple whitespace characters in value with a single space.
+Replace multiple whitespace characters in `value` (`string`) with a single
+space.
 
 ## License
 
diff --git a/tsconfig.json b/tsconfig.json
new file mode 100644
index 0000000..8ac10fe
--- /dev/null
+++ b/tsconfig.json
@@ -0,0 +1,16 @@
+{
+  "files": ["index.js"],
+  "include": ["*.js"],
+  "compilerOptions": {
+    "target": "ES2020",
+    "lib": ["ES2020"],
+    "module": "ES2020",
+    "moduleResolution": "node",
+    "allowJs": true,
+    "checkJs": true,
+    "declaration": true,
+    "emitDeclarationOnly": true,
+    "allowSyntheticDefaultImports": true,
+    "skipLibCheck": true
+  }
+}