diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..036b376
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,12 @@
+name: CI
+on:
+  pull_request:
+  push:
+
+jobs:
+  typecheck:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - run: npm i
+      - run: tsc
diff --git a/package.json b/package.json
index 6658106..fa09617 100644
--- a/package.json
+++ b/package.json
@@ -11,6 +11,8 @@
     "test": "vitest run"
   },
   "devDependencies": {
+    "@types/node": "20.14.2",
+    "typescript": "5.4.5",
     "vitest": "1.6.0"
   }
 }
diff --git a/src/chat.js b/src/chat.js
index ce33c66..2009d96 100644
--- a/src/chat.js
+++ b/src/chat.js
@@ -11,6 +11,9 @@ const systemPrompt = 'You are a machine learning web application named "hyperpar
   'The quickest way to get started is to upload a dataset and start exploring.'
 const messages = [{ role: 'system', content: systemPrompt }]
 
+/**
+ * @param {Object} chatInput
+ */
 function sendToServer(chatInput) {
   return new Promise((resolve, reject) => {
     const json = JSON.stringify(chatInput)
@@ -44,6 +47,9 @@ function sendToServer(chatInput) {
   })
 }
 
+/**
+ * @param {string[]} args
+ */
 function write(...args) {
   args.forEach(s => process.stdout.write(s))
 }
@@ -60,7 +66,7 @@ function chat() {
 
   write(colors.system, 'question: ', colors.normal)
 
-  process.stdin.on('data', async (input) => {
+  process.stdin.on('data', async (/** @type {string} */ input) => {
     input = input.trim()
     if (input === 'exit') {
       process.exit()
diff --git a/src/cli.js b/src/cli.js
index 19bbd0c..b0c029a 100644
--- a/src/cli.js
+++ b/src/cli.js
@@ -2,7 +2,6 @@
 
 if (process.argv[2] === 'chat') {
   require('./chat').chat()
-  return
 } else {
   console.log('usage: hyperparam chat')
 }
diff --git a/tsconfig.json b/tsconfig.json
new file mode 100644
index 0000000..c3afbc1
--- /dev/null
+++ b/tsconfig.json
@@ -0,0 +1,12 @@
+{
+  "compilerOptions": {
+    "allowJs": true,
+    "checkJs": true,
+    "lib": ["esnext", "dom"],
+    "module": "nodenext",
+    "noEmit": true,
+    "resolveJsonModule": true,
+    "strict": true,
+  },
+  "include": ["src", "test"]
+}