diff --git a/snowpack/src/commands/build.ts b/snowpack/src/commands/build.ts
index 1892ba1ef4..3bb15c2d25 100644
--- a/snowpack/src/commands/build.ts
+++ b/snowpack/src/commands/build.ts
@@ -26,11 +26,18 @@ import {
   relativeURL,
   removeLeadingSlash,
   replaceExt,
+  HMR_CLIENT_CODE,
 } from '../util';
 import {getInstallTargets, run as installRunner} from './install';
+import { EsmHmrEngine } from '../hmr-server-engine';
 
 const CONCURRENT_WORKERS = require('os').cpus().length;
 
+let hmrEngine: EsmHmrEngine | null = null;
+function getIsHmrEnabled(config: SnowpackConfig) {
+  return config.buildOptions.watch && config.devOptions.hmr;
+}
+
 async function installOptimizedDependencies(
   scannedFiles: SnowpackSourceFile[],
   installDest: string,
@@ -139,7 +146,7 @@ class FileBuilder {
           case '.html': {
             code = wrapHtmlResponse({
               code,
-              hmr: false,
+              hmr: getIsHmrEnabled(this.config),
               isDev: false,
               config: this.config,
               mode: 'production',
@@ -289,6 +296,10 @@ export async function command(commandOptions: CommandOptions) {
 
   // Write the `import.meta.env` contents file to disk
   await fs.writeFile(path.join(internalFilesBuildLoc, 'env.js'), generateEnvModule('production'));
+  if (getIsHmrEnabled(config)) {
+    await fs.writeFile(path.resolve(internalFilesBuildLoc, 'hmr.js'), HMR_CLIENT_CODE);
+    hmrEngine = new EsmHmrEngine();
+  }
 
   logger.info(colors.yellow('! building source…'));
   const buildStart = performance.now();
@@ -449,6 +460,10 @@ export async function command(commandOptions: CommandOptions) {
         await changedPipelineFile.writeProxyToDisk(builtFile);
       }
     }
+
+    if (hmrEngine) {
+      hmrEngine.broadcastMessage({type: 'reload'});
+    }
   }
   const watcher = chokidar.watch(
     mountedDirectories.map(([dirDisk]) => dirDisk),
diff --git a/snowpack/src/commands/dev.ts b/snowpack/src/commands/dev.ts
index f299a72884..91a6b0873a 100644
--- a/snowpack/src/commands/dev.ts
+++ b/snowpack/src/commands/dev.ts
@@ -29,7 +29,7 @@ import isCompressible from 'compressible';
 import merge from 'deepmerge';
 import etag from 'etag';
 import {EventEmitter} from 'events';
-import {createReadStream, existsSync, promises as fs, readFileSync, statSync} from 'fs';
+import {createReadStream, existsSync, promises as fs, statSync} from 'fs';
 import http from 'http';
 import HttpProxy from 'http-proxy';
 import http2 from 'http2';
@@ -76,10 +76,10 @@ import {
   replaceExt,
   resolveDependencyManifest,
   updateLockfileHash,
+  HMR_CLIENT_CODE,
 } from '../util';
 import {command as installCommand} from './install';
 import {getPort, paint, paintEvent} from './paint';
-const HMR_DEV_CODE = readFileSync(path.join(__dirname, '../assets/hmr.js'));
 
 const DEFAULT_PROXY_ERROR_HANDLER = (
   err: Error,
@@ -203,7 +203,8 @@ function getUrlFromFile(
 
 export async function command(commandOptions: CommandOptions) {
   const {cwd, config} = commandOptions;
-  const {port: defaultPort, hostname, open, hmr: isHmr} = config.devOptions;
+  const {port: defaultPort, hostname, open } = config.devOptions;
+  const isHmr = config.devOptions.hmr || true;
 
   // Start the startup timer!
   let serverStart = performance.now();
@@ -365,7 +366,7 @@ export async function command(commandOptions: CommandOptions) {
     });
 
     if (reqPath === getMetaUrlPath('/hmr.js', config)) {
-      sendFile(req, res, HMR_DEV_CODE, reqPath, '.js');
+      sendFile(req, res, HMR_CLIENT_CODE, reqPath, '.js');
       return;
     }
     if (reqPath === getMetaUrlPath('/env.js', config)) {
diff --git a/snowpack/src/hmr-server-engine.ts b/snowpack/src/hmr-server-engine.ts
index b888750664..690e3fdf42 100644
--- a/snowpack/src/hmr-server-engine.ts
+++ b/snowpack/src/hmr-server-engine.ts
@@ -11,14 +11,17 @@ interface Dependency {
   needsReplacementCount: number;
 }
 
+const DEFAULT_PORT = 12321;
+
 export class EsmHmrEngine {
   clients: Set<WebSocket> = new Set();
   dependencyTree = new Map<string, Dependency>();
+  wsUrl = `ws://localhost:${DEFAULT_PORT}`;
 
   constructor(options: {server?: http.Server | http2.Http2Server} = {}) {
     const wss = options.server
       ? new WebSocket.Server({noServer: true})
-      : new WebSocket.Server({port: 12321});
+      : new WebSocket.Server({port: DEFAULT_PORT});
     if (options.server) {
       options.server.on('upgrade', (req, socket, head) => {
         // Only handle upgrades to ESM-HMR requests, ignore others.
diff --git a/snowpack/src/util.ts b/snowpack/src/util.ts
index f4fcd2f34f..2a4d50cac8 100644
--- a/snowpack/src/util.ts
+++ b/snowpack/src/util.ts
@@ -409,3 +409,5 @@ export function removeLeadingSlash(path: string) {
 export function removeTrailingSlash(path: string) {
   return path.replace(/[/\\]+$/, '');
 }
+
+export const HMR_CLIENT_CODE = fs.readFileSync(path.join(__dirname, '../assets/hmr.js'), 'utf-8');
\ No newline at end of file