withastro · ematipico · Mar 26, 2026 · Mar 24, 2026 · Mar 24, 2026
diff --git a/.changeset/moody-turkeys-agree.md b/.changeset/moody-turkeys-agree.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes an issue with the development server, where changes to the middleware weren't picked, and it required a full restart of the server.
diff --git a/packages/astro/e2e/fixtures/hmr/src/middleware.ts b/packages/astro/e2e/fixtures/hmr/src/middleware.ts
@@ -0,0 +1,9 @@
+import { defineMiddleware } from 'astro:middleware';
+
+export const onRequest = defineMiddleware((_context, next) => {
+	const response = next();
+	response.then((res) => {
+		res.headers.set('x-test-middleware', 'before');
+	});
+	return response;
+});
diff --git a/packages/astro/e2e/fixtures/hmr/src/pages/middleware-test.astro b/packages/astro/e2e/fixtures/hmr/src/pages/middleware-test.astro
@@ -0,0 +1,8 @@
+<html>
+	<head>
+		<title>Middleware HMR Test</title>
+	</head>
+	<body>
+		<h1>Middleware HMR</h1>
+	</body>
+</html>
diff --git a/packages/astro/e2e/hmr.test.js b/packages/astro/e2e/hmr.test.js
@@ -123,3 +123,23 @@ test.describe('Styles', () => {
 		await expect(h).toHaveCSS('color', 'rgb(0, 0, 0)');
 	});
 });
+
+test.describe('Middleware', () => {
+	test('middleware changes are picked up without restart', async ({ astro }) => {
+		// Verify original middleware header
+		const res1 = await astro.fetch('/middleware-test');
+		expect(res1.headers.get('x-test-middleware')).toBe('before');
+
+		// Edit middleware to change the header value
+		await astro.editFile('./src/middleware.ts', (original) =>
+			original.replace("'before'", "'after'"),
+		);
+
+		// Wait briefly for HMR to propagate
+		await new Promise((resolve) => setTimeout(resolve, 1000));
+
+		// Verify the new header value is returned without server restart
+		const res2 = await astro.fetch('/middleware-test');
+		expect(res2.headers.get('x-test-middleware')).toBe('after');
+	});
+});
diff --git a/packages/astro/src/core/app/dev/app.ts b/packages/astro/src/core/app/dev/app.ts
@@ -36,6 +36,14 @@ export class DevApp extends BaseApp<NonRunnablePipeline> {
 		return true;
 	}
 
+	/**
+	 * Clears the cached middleware so it is re-resolved on the next request.
+	 * Called via HMR when middleware files change.
+	 */
+	clearMiddleware(): void {
+		this.pipeline.clearMiddleware();
+	}
+
 	/**
 	 * Updates the routes list when files change during development.
 	 * Called via HMR when new pages are added/removed.

diff --git a/packages/astro/src/core/app/entrypoints/virtual/dev.ts b/packages/astro/src/core/app/entrypoints/virtual/dev.ts
@@ -33,6 +33,13 @@ export const createApp: CreateApp = ({ streaming } = {}) => {
 			if (!currentDevApp) return;
 			currentDevApp.pipeline.routeCache.clearAll();
 		});
+
+		// Listen for middleware file changes via HMR.
+		// Clear the cached middleware so it is re-resolved on the next request.
+		import.meta.hot.on('astro:middleware-updated', () => {
+			if (!currentDevApp) return;
+			currentDevApp.clearMiddleware();
+		});
 	}
 
 	return currentDevApp;

diff --git a/packages/astro/src/core/base-pipeline.ts b/packages/astro/src/core/base-pipeline.ts
@@ -154,6 +154,14 @@ export abstract class Pipeline {
 		}
 	}
 
+	/**
+	 * Clears the cached middleware so it is re-resolved on the next request.
+	 * Called via HMR when middleware files change during development.
+	 */
+	clearMiddleware() {
+		this.resolvedMiddleware = undefined;
+	}
+
 	async getActions(): Promise<SSRActions> {
 		if (this.resolvedActions) {
 			return this.resolvedActions;

diff --git a/packages/astro/src/core/middleware/vite-plugin.ts b/packages/astro/src/core/middleware/vite-plugin.ts
@@ -1,4 +1,9 @@
-import type { Plugin as VitePlugin } from 'vite';
+import { fileURLToPath } from 'node:url';
+import {
+	normalizePath as viteNormalizePath,
+	type ViteDevServer,
+	type Plugin as VitePlugin,
+} from 'vite';
 import { getServerOutputDirectory } from '../../prerender/utils.js';
 import type { AstroSettings } from '../../types/astro.js';
 import { addRollupInput } from '../build/add-rollup-input.js';
@@ -21,6 +26,8 @@ export function vitePluginMiddleware({ settings }: { settings: AstroSettings }):
 		settings.middlewares.pre.length > 0 || settings.middlewares.post.length > 0;
 	let userMiddlewareIsPresent = false;
 
+	const normalizedSrcDir = viteNormalizePath(fileURLToPath(settings.config.srcDir));
+
 	return {
 		name: '@astro/plugin-middleware',
 		applyToEnvironment(environment) {
@@ -30,6 +37,31 @@ export function vitePluginMiddleware({ settings }: { settings: AstroSettings }):
 				environment.name === ASTRO_VITE_ENVIRONMENT_NAMES.prerender
 			);
 		},
+		configureServer(server: ViteDevServer) {
+			server.watcher.on('change', (path) => {
+				const normalizedPath = viteNormalizePath(path);
+				// Check if the changed file is a middleware file under srcDir
+				if (!normalizedPath.startsWith(normalizedSrcDir)) return;
+				const relativePath = normalizedPath.slice(normalizedSrcDir.length);
+				// Dot ensures we match "middleware.ts" but not e.g. "middleware-utils.ts"
+				if (!relativePath.startsWith(`${MIDDLEWARE_PATH_SEGMENT_NAME}.`)) return;
+
+				for (const name of [
+					ASTRO_VITE_ENVIRONMENT_NAMES.ssr,
+					ASTRO_VITE_ENVIRONMENT_NAMES.astro,
+				] as const) {
+					const environment = server.environments[name];
+					if (!environment) continue;
+
+					const virtualMod = environment.moduleGraph.getModuleById(MIDDLEWARE_RESOLVED_MODULE_ID);
+					if (virtualMod) {
+						environment.moduleGraph.invalidateModule(virtualMod);
+					}
+
+					environment.hot.send('astro:middleware-updated', {});
+				}
+			});
+		},
 		resolveId: {
 			filter: {
 				id: new RegExp(`^${MIDDLEWARE_MODULE_ID}$`),

diff --git a/packages/astro/src/vite-plugin-app/app.ts b/packages/astro/src/vite-plugin-app/app.ts
@@ -70,6 +70,14 @@ export class AstroServerApp extends BaseApp<RunnablePipeline> {
 		this.pipeline.clearRouteCache();
 	}
 
+	/**
+	 * Clears the cached middleware so it is re-resolved on the next request.
+	 * Called via HMR when middleware files change.
+	 */
+	clearMiddleware(): void {
+		this.pipeline.clearMiddleware();
+	}
+
 	async devMatch(pathname: string): Promise<DevMatch | undefined> {
 		const matchedRoute = await matchRoute(
 			pathname,

diff --git a/packages/astro/src/vite-plugin-app/createAstroServerApp.ts b/packages/astro/src/vite-plugin-app/createAstroServerApp.ts
@@ -78,6 +78,13 @@ export default async function createAstroServerApp(
 			app.clearRouteCache();
 			actualLogger.debug('router', 'Route cache cleared due to content change');
 		});
+
+		// Listen for middleware file changes via HMR.
+		// Clear the cached middleware so it is re-resolved on the next request.
+		import.meta.hot.on('astro:middleware-updated', () => {
+			app.clearMiddleware();
+			actualLogger.debug('router', 'Middleware cache cleared due to file change');
+		});
 	}
 
 	return {