diff --git a/README.md b/README.md
index 098f7c8..0796203 100644
--- a/README.md
+++ b/README.md
@@ -17,6 +17,13 @@ Read [Dohna NS Documentation](https://dohna-ns.sbs/) to learn how to install Doh
 | Vercel     | [![Deploy to Vercel](https://vercel.com/button)](https://vercel.com/new/clone?repository-url=https://github.com/LittleChest/Dohna-NS)                          |
 | Netlify    | [![Deploy to Netlify](https://www.netlify.com/img/deploy/button.svg)](https://app.netlify.com/start/deploy?repository=https://github.com/LittleChest/Dohna-NS) |
 
+## Environment Variables
+
+| Key | Default                      | Description                                      |
+| --- | ---------------------------- | ------------------------------------------------ |
+| DNS | https://dns.google/dns-query | Specify a DNS over HTTPS server as the upstream. |
+| API | https://dns.google/resolve   | Specify a JSON API server as the upstream.       |
+
 ## Self-hosted
 
 You can use [Netlify CLI](https://cli.netlify.com/commands/serve/) or [`workerd`](https://github.com/cloudflare/workerd/blob/main/README.md#getting-started) **(Recommended)** to serve locally.
diff --git a/_worker.js b/_worker.js
index bb27634..5ff5896 100644
--- a/_worker.js
+++ b/_worker.js
@@ -1,5 +1,5 @@
 import handler from "./common";
 
 export default {
-  fetch: async (request) => handler(request),
+  fetch: async (request, env) => handler(request, env.DNS, env.API),
 };
diff --git a/common.js b/common.js
index c0a409d..0ee3e4d 100644
--- a/common.js
+++ b/common.js
@@ -1,7 +1,8 @@
-const dns = "https://dns.google/dns-query";
-const api = "https://dns.google/resolve";
-
-export default async function handler(request) {
+export default async function handler(
+  request,
+  dns = "https://dns.google/dns-query",
+  api = "https://dns.google/resolve"
+) {
   const { method, headers, url } = request;
   const { search, searchParams, pathname } = new URL(url);
   const ip = headers.get("x-forwarded-for");
@@ -57,14 +58,14 @@ export default async function handler(request) {
     }
 
     if (queryData !== undefined) {
-      res = await queryDns(queryData, ip);
+      res = await queryDns(queryData, ip, dns);
     }
   }
 
   return res;
 }
 
-async function queryDns(queryData, ip) {
+async function queryDns(queryData, ip, dns) {
   const hasOptRecord = checkForOptRecord(queryData);
   let newQueryData = queryData;
   if (!hasOptRecord && ip) {
diff --git a/middleware.js b/middleware.js
index 4d7ddf8..2259bb7 100644
--- a/middleware.js
+++ b/middleware.js
@@ -1,5 +1,5 @@
 import handler from "./common";
 
 export default middleware = async (request) => {
-  return handler(request);
+  return handler(request, process.env.DNS, process.env.API);
 };
diff --git a/netlify/edge-functions/middleware.js b/netlify/edge-functions/middleware.js
index 3304002..5b1d535 100644
--- a/netlify/edge-functions/middleware.js
+++ b/netlify/edge-functions/middleware.js
@@ -1,3 +1,4 @@
 import handler from "../../common.js";
-export default (request) => handler(request);
+export default (request) =>
+  handler(request, Netlify.env.get("DNS"), Netlify.env.get("API"));
 export const config = { path: "*" };