diff --git a/.github/workflows/check.yml b/.github/workflows/check.yml
new file mode 100644
index 0000000..f7c3e62
--- /dev/null
+++ b/.github/workflows/check.yml
@@ -0,0 +1,31 @@
+name: Checks
+
+on:
+  workflow_dispatch: {}
+  pull_request:
+    types:
+      - opened
+      - synchronize
+
+jobs:
+  checks:
+    name: Checks
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Install Node
+        uses: actions/setup-node@v2
+        with:
+          node-version: 18
+
+      - name: Dependencies
+        run: npm ci
+
+      - name: Lint
+        run: npm run lint:ci
+
+      - name: Format
+        run: npm run format:ci
diff --git a/package.json b/package.json
index 0b82145..ff40085 100644
--- a/package.json
+++ b/package.json
@@ -7,7 +7,10 @@
   "scripts": {
     "build": "esbuild src/index.ts --bundle --outfile=dist/index.js",
     "test": "eslint src/**/*.ts && tsc --noEmit",
-    "format": "prettier --write 'src/**/*.{ts,tsx,json}'"
+    "lint": "eslint --fix --ext .tsx,.ts src/",
+    "lint:ci": "eslint --ext .tsx,.ts src/ --max-warnings 0",
+    "format": "prettier --write 'src/**/*.{ts,tsx}'",
+    "format:ci": "prettier --check 'src/**/*.{ts,tsx}'"
   },
   "author": "Alexander Borsuk <me@alex.bio>",
   "license": "MIT",
diff --git a/src/index.ts b/src/index.ts
index 678136e..f5744be 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,4 +1,4 @@
-export { };
+export {};
 
 // TODO: Implement automated version checks from this metaserver script.
 // It should check by cron if actual files are really available on all servers.
@@ -6,38 +6,41 @@ const SERVER = {
   backblaze: {
     // BackBlaze + CloudFlare (US-West) unmetered.
     url: 'https://cdn-us1.organicmaps.app/',
-    dataVersions: [210529, 210703, 210729, 210825, 211002, 211022, 211122, 220103, 220204, 220314, 220415, 220515, 220613, 220718, 220816]
+    dataVersions: [
+      210529, 210703, 210729, 210825, 211002, 211022, 211122, 220103, 220204, 220314, 220415, 220515, 220613, 220718,
+      220816,
+    ],
   },
   uk1: {
     // Mythic Beasts VPS (London, UK) 200TB/mo.
     url: 'https://cdn-uk1.organicmaps.app/',
-    dataVersions: [220613, 220718, 220816]
+    dataVersions: [220613, 220718, 220816],
   },
   nl1: {
     // // Mythic Beasts VPS (Amsterdam, NL) 200TB/mo.
     url: 'https://cdn-nl1.organicmaps.app/',
-    dataVersions: [220613, 220718, 220816]
+    dataVersions: [220613, 220718, 220816],
   },
   planet: {
     // Hetzner BareMetal (Falkenstein, Germany) unmetered
     url: 'https://cdn.organicmaps.app/',
-    dataVersions: [220103, 220204, 220314, 220415, 220515, 220613, 220718, 220816]
+    dataVersions: [220103, 220204, 220314, 220415, 220515, 220613, 220718, 220816],
   },
   fi1: {
     // Hetzner Cloud (Helsinki, Finland), 20TB/mo
     url: 'https://cdn-fi1.organicmaps.app/',
-    dataVersions: [220718, 220816]
+    dataVersions: [220718, 220816],
   },
   de1: {
     // Hetzner Cloud (Falkenstein, Germany), 20TB/mo
     url: 'https://cdn-eu2.organicmaps.app/',
-    dataVersions: [220718, 220816]
+    dataVersions: [220718, 220816],
   },
   us2: {
     // Hetzner Cloud (Asburn, US East), 20TB/mo
     url: 'https://cdn-us2.organicmaps.app/',
-    dataVersions: [220718, 220816]
-  }
+    dataVersions: [220718, 220816],
+  },
 };
 
 // Main entry point.
@@ -53,8 +56,9 @@ function extractDataVersion(request: Request): number {
   const strDataVersion = request.headers.get('x-om-dataversion');
   if (strDataVersion) {
     const dataVersion = parseInt(strDataVersion);
-    if (!Number.isNaN(dataVersion) && dataVersion >= 210000 && dataVersion <= 500000)
+    if (!Number.isNaN(dataVersion) && dataVersion >= 210000 && dataVersion <= 500000) {
       return dataVersion;
+    }
   }
   return 0;
 }
@@ -63,39 +67,42 @@ async function handleRequest(request: Request) {
   const { pathname } = new URL(request.url);
 
   switch (pathname) {
-    case '/maps':       // Public for map files.
-    case '/resources':  // Public for resources.
-    case '/servers': {  // Private for map files.
+    case '/maps': // Public for map files.
+    case '/resources': // Public for resources.
+    case '/servers': {
+      // Private for map files.
       let servers;
       const dataVersion = extractDataVersion(request);
       if (dataVersion == 0) {
-        servers = [SERVER.backblaze]
-      } else switch (request.cf?.continent) {
-        // See https://developers.cloudflare.com/firewall/cf-firewall-language/fields for a list of all continents.
-        case 'NA': // North America
-        case 'SA': // South America
-        case 'OC': // Oceania
-          servers = [SERVER.backblaze, SERVER.us2, SERVER.uk1, SERVER.nl1, SERVER.planet]
-            .filter(server => server.dataVersions.includes(dataVersion))
-          if (servers.length == 0) {
-            servers = [SERVER.planet]
-          }
-          break;
-        default: // Every other continent + Tor networks.
-          servers = [SERVER.planet, SERVER.uk1, SERVER.nl1, SERVER.fi1, SERVER.de1]
-            .filter(server => server.dataVersions.includes(dataVersion))
-          if (servers.length == 0) {
-            if (SERVER.backblaze.dataVersions.includes(dataVersion)) {
-              servers = [SERVER.backblaze]
-            } else {
-              servers = [SERVER.planet]
+        servers = [SERVER.backblaze];
+      } else
+        switch (request.cf?.continent) {
+          // See https://developers.cloudflare.com/firewall/cf-firewall-language/fields for a list of all continents.
+          case 'NA': // North America
+          case 'SA': // South America
+          case 'OC': // Oceania
+            servers = [SERVER.backblaze, SERVER.us2, SERVER.uk1, SERVER.nl1, SERVER.planet].filter((server) =>
+              server.dataVersions.includes(dataVersion),
+            );
+            if (servers.length == 0) {
+              servers = [SERVER.planet];
             }
-          }
-      }
+            break;
+          default:
+            // Every other continent + Tor networks.
+            servers = [SERVER.planet, SERVER.uk1, SERVER.nl1, SERVER.fi1, SERVER.de1].filter((server) =>
+              server.dataVersions.includes(dataVersion),
+            );
+            if (servers.length == 0) {
+              if (SERVER.backblaze.dataVersions.includes(dataVersion)) {
+                servers = [SERVER.backblaze];
+              } else {
+                servers = [SERVER.planet];
+              }
+            }
+        }
 
-      let donation
-
-      const response = servers.map(server => server.url)
+      const response = servers.map((server) => server.url);
       return new Response(JSON.stringify(response), {
         headers: { 'Content-Type': 'application/json' },
       });