@@ -94,6 +94,8 @@ Pages can be flat files such as `about.vue` or directory-based routes such as `a
 
 <PagesFileTree />
 
+Keep one file per route. Void reports an error when two page files resolve to the same path, such as `about.vue` and `about/index.vue`, or the same page in two route groups.
+
 Each page can have a companion `.server.ts` file that runs exclusively on the server. It can export:
 
 - A [**loader**](./loaders), which runs on `GET` and returns the data that becomes the page component's props
 
@@ -48,7 +48,8 @@ export type ReactPagesConfig = Readonly<{
   components: Record<string, () => Promise<ComponentModule>>;
   layoutTree: Record<string, Array<string>>;
   routeMeta: Record<string, { island?: boolean }>;
-  matchRoute(url: string): string | null;
+  /** Page id for a decoded pathname. */
+  matchRoute(path: string): string | null;
   staticPageData: boolean;
   staticPageDataFastPath: boolean;
   viewTransitions: boolean;
 
@@ -10,6 +10,8 @@ export async function completeApplicationAnalysis(
   const scan = await scanRoutes(analysis.root, {
     output: analysis.config.output,
     paths: analysis.paths,
+    // A framework app's pages/ follows that framework's rules, not Void Pages.
+    checkPageRoutes: !analysis.framework,
     inventory: {
       routes: analysis.routes,
       middleware: analysis.middleware,
 
@@ -8,11 +8,24 @@ import type { PageScanResult } from './types.ts';
  * Client entries load this eagerly, so it grows with every page. Each page id
  * is written once, identical layout chains are shared, and static routes are
  * matched by exact lookup instead of a RegExp per page. The emitted bindings
- * (`components`, `layoutTree`, `routeMeta`, `matchRoute`) keep their shape.
+ * (`components`, `layoutTree`, `routeMeta`, `matchRoute`) keep their shape;
+ * `matchRoute` takes a decoded pathname (see `decodePagePath`).
  */
 export function generateComponentManifest(scan: PageScanResult, pagesDir: string): string {
   const load = (filePath: string) => `() => import(${JSON.stringify(`${pagesDir}/${filePath}`)})`;
 
+  // A page in a folder named "layout" (layout/index.tsx) has the id of the
+  // layout file beside it (layout.tsx). No page path has a segment starting
+  // with "_", so that layout is keyed "_layout" instead.
+  const pageIds = new Set(scan.pages.map((page) => page.componentId));
+  const layoutKey = (id: string): string => {
+    if (!pageIds.has(id)) {
+      return id;
+    }
+    const slash = id.lastIndexOf('/');
+    return id.slice(0, slash + 1) + '_' + id.slice(slash + 1);
+  };
+
   const chains: Array<string> = [];
   const chainIndexes = new Map<string, number>();
   const staticRows: Array<string> = [];
@@ -21,7 +34,9 @@ export function generateComponentManifest(scan: PageScanResult, pagesDir: string
   // can be looked up exactly without changing which route matches first.
   let inStaticPrefix = true;
   for (const page of scan.pages) {
-    const chain = JSON.stringify(resolveLayoutIds(page, scan.layouts, scan.namedLayouts));
+    const chain = JSON.stringify(
+      resolveLayoutIds(page, scan.layouts, scan.namedLayouts).map(layoutKey),
+    );
     let chainIndex = chain === '[]' ? -1 : chainIndexes.get(chain);
     if (chainIndex === undefined) {
       chainIndex = chains.push(chain) - 1;
@@ -60,9 +75,10 @@ for (const [pattern, id, load, chain] of __voidDynamicRoutes) {
   if (chain >= 0) layoutTree[id] = __voidLayoutChains[chain];
   routes.push({ pattern, id });
 }`);
-  // Layouts are set after pages, so a layout keeps an id it shares with a page.
   for (const layout of [...scan.layouts, ...scan.namedLayouts]) {
-    lines.push(`components[${JSON.stringify(toLayoutId(layout))}] = ${load(layout.filePath)};`);
+    lines.push(
+      `components[${JSON.stringify(layoutKey(toLayoutId(layout)))}] = ${load(layout.filePath)};`,
+    );
   }
 
   // Route metadata (sparse — only island pages)
@@ -74,8 +90,7 @@ for (const [pattern, id, load, chain] of __voidDynamicRoutes) {
   }
   lines.push('};');
 
-  lines.push(`function matchRoute(url) {
-  const path = new URL(url, "http://x").pathname;
+  lines.push(`function matchRoute(path) {
   const id = __voidStaticRouteIds.get(path);
   if (id !== undefined) return id;
   for (const r of routes) {
@@ -106,7 +121,8 @@ function isStaticPattern(pattern: string): boolean {
   return pattern.split('/').every((segment) => captureGroup(segment) === undefined);
 }
 
-function patternToRegex(pattern: string): string {
+/** The RegExp literal a page pattern matches with, the same on the client and the server. */
+export function patternToRegex(pattern: string): string {
   const regexSource = pattern
     .split('/')
     .map((segment) => {
 
@@ -8,7 +8,7 @@ import { PrefetchCache, parseCacheFor } from './prefetch.ts';
 import type { CacheForInput, CacheForResult } from './prefetch.ts';
 import type { PageObject } from './protocol.ts';
 import { createScrollRestoration } from './scroll-restoration.ts';
-import { isSameOrigin } from './url.ts';
+import { decodePagePath, isSameOrigin } from './url.ts';
 
 /**
  * The server leaves a named action's key out of the page URL. When the page URL
@@ -77,7 +77,8 @@ export type PageNavigationEngineConfig = {
   components: Record<string, () => Promise<PageComponentModule>>;
   layoutTree: Record<string, Array<string>>;
   routeMeta: Record<string, { island?: boolean }>;
-  matchRoute(url: string): string | null;
+  /** Page id for a decoded pathname (see `decodePagePath`). */
+  matchRoute(path: string): string | null;
   staticPageData?: boolean;
   staticPageDataFastPath?: boolean;
   viewTransitions: boolean;
@@ -239,14 +240,16 @@ export async function createPageNavigationEngine(
     components,
     layoutTree,
     routeMeta,
-    matchRoute,
     staticPageData: STATIC_PAGE_DATA_ENABLED = false,
     staticPageDataFastPath: STATIC_PAGE_DATA_FAST_PATH = STATIC_PAGE_DATA_ENABLED,
     prefetchHoverDelay: PREFETCH_HOVER_DELAY,
     prefetchDefaultCacheFor: PREFETCH_DEFAULT_CACHE_FOR,
     cacheVisitedPageData: CACHE_VISITED_PAGE_DATA = false,
   } = config;
 
+  const matchRoute = (url: string) =>
+    config.matchRoute(decodePagePath(new URL(url, 'http://x').pathname));
+
   const _prefetchCache = new PrefetchCache();
   let _nextNavigationId = 0;
   let _pendingResource: PageNavigationResource | null = null;
 
@@ -19,6 +19,7 @@ import {
 import { staticExportInitializers, staticLiteral } from '../shared/static-exports.ts';
 import { scriptBlocks } from './island-imports.ts';
 import { resolveNamedLayout } from './layout-resolution.ts';
+import { patternToRegex } from './manifest.ts';
 import type {
   ExplicitBoolean,
   PageDefinition,
@@ -37,6 +38,8 @@ export const MAX_REVALIDATE = 31536000; // 1 year in seconds
 
 /** Layout paths already reported; a dev server rescans pages on every file change. */
 const warnedLayoutPaths = new Set<string>();
+/** Unreachable pages already reported, for the same reason. */
+const warnedShadowedPages = new Set<string>();
 
 type PageRenderingSource = {
   componentPath: string;
@@ -49,7 +52,13 @@ type PageRenderingSource = {
   hasGetPrerenderPaths?: boolean;
 };
 
-type PageScanOptions = { output?: 'server' | 'static'; paths?: ProjectPaths; pagesDir?: string };
+type PageScanOptions = {
+  output?: 'server' | 'static';
+  paths?: ProjectPaths;
+  pagesDir?: string;
+  /** Report pages that share a route. Off when another framework owns pages/ (Nuxt nests users.vue and users/index.vue). */
+  checkRoutes?: boolean;
+};
 
 type ResolvedPageRendering = {
   ssrMode: SsrMode;
@@ -363,6 +372,11 @@ export async function scanPages(root: string, options?: PageScanOptions): Promis
     return a.pattern.localeCompare(b.pattern);
   });
 
+  if (options?.checkRoutes !== false) {
+    assertOnePagePerRoute(pages);
+    warnShadowedPages(pagesDir, pages);
+  }
+
   // Validate: throw when regular pages are under island layouts
   for (const page of pages) {
     if (page.island) {
@@ -405,6 +419,84 @@ export async function scanPages(root: string, options?: PageScanOptions): Promis
   return { pages, layouts, namedLayouts };
 }
 
+function compareText(left: string, right: string): number {
+  return left < right ? -1 : left > right ? 1 : 0;
+}
+
+/** Group sorted pages by `key`, keeping only groups with more than one page. */
+function pagesSharing(
+  pages: Array<PageDefinition>,
+  key: (page: PageDefinition) => string,
+): Array<Array<PageDefinition>> {
+  const groups = new Map<string, Array<PageDefinition>>();
+  for (const page of pages) {
+    const group = groups.get(key(page));
+    if (group) {
+      group.push(page);
+    } else {
+      groups.set(key(page), [page]);
+    }
+  }
+  return [...groups.values()].filter((group) => group.length > 1);
+}
+
+/**
+ * Two files for one path have no stable winner: the server and the client can
+ * each pick a different one, and the order can change between runs.
+ */
+function assertOnePagePerRoute(pages: Array<PageDefinition>): void {
+  assertNoneShare(
+    pages,
+    (page) => page.pattern,
+    'pages: Multiple page files resolve to the same route:',
+    'Keep one page file per route and rename or remove the others.',
+  );
+  // index.tsx and index/index.tsx have different routes but the same page id.
+  assertNoneShare(
+    pages,
+    (page) => page.componentId,
+    'pages: Multiple page files resolve to the same page id:',
+    'Rename or remove one of them.',
+  );
+}
+
+function assertNoneShare(
+  pages: Array<PageDefinition>,
+  key: (page: PageDefinition) => string,
+  title: string,
+  hint: string,
+): void {
+  const clashes = pagesSharing(pages, key)
+    .map((group) => ({
+      key: key(group[0]),
+      files: group.map((page) => page.componentPath).sort(compareText),
+    }))
+    .sort((left, right) => compareText(left.key, right.key))
+    .map(
+      (clash) =>
+        `  ${JSON.stringify(clash.key)}: ${clash.files.map((file) => JSON.stringify(file)).join(', ')}`,
+    );
+  if (clashes.length > 0) {
+    throw new Error([title, ...clashes, hint].join('\n'));
+  }
+}
+
+/** Dynamic routes that match the same URLs, such as [id] and [slug]: only the first is ever used. */
+function warnShadowedPages(pagesDir: string, pages: Array<PageDefinition>): void {
+  for (const [used, ...shadowed] of pagesSharing(pages, (page) => patternToRegex(page.pattern))) {
+    for (const page of shadowed) {
+      const key = `${pagesDir}\0${used.componentPath}\0${page.componentPath}`;
+      if (warnedShadowedPages.has(key)) {
+        continue;
+      }
+      warnedShadowedPages.add(key);
+      voidWarn(
+        `pages: Page '${page.componentPath}' (${page.pattern}) is never used: '${used.componentPath}' (${used.pattern}) matches the same URLs first. Remove one of them.`,
+      );
+    }
+  }
+}
+
 // Same leading-script rule as @void/md's extractScript: a markdown page may open
 // with a <script> block, and its frontmatter starts right after that block.
 const LEADING_SCRIPT_RE = /^<script\b[^>]*>[\s\S]*?<\/script>\s*\n?/;
 
@@ -6,3 +6,50 @@ export function isSameOrigin(url: URL, origin: string): boolean {
   }
   return url.origin === origin;
 }
+
+function isHexDigit(char: string | undefined): boolean {
+  return (
+    char !== undefined &&
+    ((char >= '0' && char <= '9') || (char >= 'a' && char <= 'f') || (char >= 'A' && char <= 'F'))
+  );
+}
+
+function tryDecodeURI(text: string): string {
+  try {
+    return decodeURI(text);
+  } catch {
+    return text;
+  }
+}
+
+/**
+ * The path a page is matched on, decoded the way the server (Hono's getPath)
+ * decodes it: `/caf%C3%A9` becomes `/café`, while `%25`, reserved escapes such
+ * as `%2F` and malformed escapes stay encoded.
+ */
+export function decodePagePath(path: string): string {
+  if (!path.includes('%')) {
+    return path;
+  }
+  const escaped = path.split('%25').join('%2525');
+  try {
+    return decodeURI(escaped);
+  } catch {
+    // Decode each run of escapes on its own, keeping the runs that fail.
+  }
+  let decoded = '';
+  let index = 0;
+  while (index < escaped.length) {
+    let end = index;
+    while (escaped[end] === '%' && isHexDigit(escaped[end + 1]) && isHexDigit(escaped[end + 2])) {
+      end += 3;
+    }
+    if (end === index) {
+      decoded += escaped[index++];
+    } else {
+      decoded += tryDecodeURI(escaped.slice(index, end));
+      index = end;
+    }
+  }
+  return decoded;
+}
@@ -680,7 +680,26 @@ export function routingPlugin(root: string, options: RoutingPluginOptions): Plug
         // Re-scan and invalidate the virtual module in ALL environments.
         // The route table virtual module lives in the workerd environment,
         // not the client — so we must iterate all environments.
-        await rescan(true);
+        try {
+          await rescan(true);
+        } catch (error) {
+          // Keep the last good route table; the next change rescans.
+          const message = error instanceof Error ? error.message : String(error);
+          // An adapter's pages plugin rescans page adds, removals and .md saves
+          // and logs the same page error, so log it once.
+          const adapterLogs =
+            message.startsWith('pages:') &&
+            isInDirectory(normalizedPath, normalizedPagesDir) &&
+            (event !== 'change' || normalizedPath.endsWith('.md')) &&
+            resolvedConfig?.plugins?.some((plugin) => plugin.name.endsWith(':pages')) === true;
+          if (!adapterLogs) {
+            devServer.config.logger.error(message, {
+              error: error instanceof Error ? error : undefined,
+              timestamp: true,
+            });
+          }
+          return;
+        }
         resolveAuthCompileOptions();
         const shouldRestartForAssetRouting =
           event !== 'change' &&
 
@@ -75,10 +75,15 @@ export async function scanRoutes(
     output?: 'server' | 'static';
     paths: ProjectPaths;
     inventory: Omit<ScanResult, 'pages'>;
+    checkPageRoutes?: boolean;
   },
 ): Promise<ScanResult> {
   const { paths, inventory } = options;
-  const pages = await scanPages(root, { output: options.output, paths });
+  const pages = await scanPages(root, {
+    output: options.output,
+    paths,
+    checkRoutes: options.checkPageRoutes,
+  });
   const routes = inventory.routes
     .map((route) => ({
       ...route,