diff --git a/.changeset/clean-brooms-drum.md b/.changeset/clean-brooms-drum.md
new file mode 100644
index 0000000000..6dfef23823
--- /dev/null
+++ b/.changeset/clean-brooms-drum.md
@@ -0,0 +1,5 @@
+---
+"@astrojs/starlight": patch
+---
+
+Improves build performance slightly for bigger sites
diff --git a/packages/starlight/user-components/FileTree.astro b/packages/starlight/user-components/FileTree.astro
index 5331146c6a..1e079cf2cd 100644
--- a/packages/starlight/user-components/FileTree.astro
+++ b/packages/starlight/user-components/FileTree.astro
@@ -1,9 +1,10 @@
 ---
+import { stripLeadingAndTrailingSlashes } from '../utils/path';
 import { slugToLocaleData } from '../utils/slugs';
 import { useTranslations } from '../utils/translations';
 import { processFileTree } from './rehype-file-tree';
 
-const slug = Astro.url.pathname.replace(/^\//, '').replace(/\/$/, '');
+const slug = stripLeadingAndTrailingSlashes(Astro.url.pathname);
 const t = useTranslations(slugToLocaleData(slug).locale);
 
 const fileTreeHtml = await Astro.slots.render('default');
diff --git a/packages/starlight/utils/localizedUrl.ts b/packages/starlight/utils/localizedUrl.ts
index 95e35f9d98..e6df9068ec 100644
--- a/packages/starlight/utils/localizedUrl.ts
+++ b/packages/starlight/utils/localizedUrl.ts
@@ -1,4 +1,5 @@
 import config from 'virtual:starlight/user-config';
+import { stripTrailingSlash } from './path';
 
 /**
  * Get the equivalent of the passed URL for the passed locale.
@@ -12,7 +13,7 @@ export function localizedUrl(url: URL, locale: string | undefined): URL {
 	}
 	if (locale === 'root') locale = '';
 	/** Base URL with trailing `/` stripped. */
-	const base = import.meta.env.BASE_URL.replace(/\/$/, '');
+	const base = stripTrailingSlash(import.meta.env.BASE_URL);
 	const hasBase = url.pathname.startsWith(base);
 	// Temporarily remove base to simplify
 	if (hasBase) url.pathname = url.pathname.replace(base, '');
diff --git a/packages/starlight/utils/navigation.ts b/packages/starlight/utils/navigation.ts
index 987e89e40c..43369be032 100644
--- a/packages/starlight/utils/navigation.ts
+++ b/packages/starlight/utils/navigation.ts
@@ -139,10 +139,10 @@ function linkFromInternalSidebarLinkItem(
 	locale: string | undefined,
 	currentPathname: string
 ) {
-	let slugWithLocale = locale ? locale + '/' + item.slug : item.slug;
 	// Astro passes root `index.[md|mdx]` entries with a slug of `index`
-	slugWithLocale = slugWithLocale.replace(/\/?index$/, '');
-	const entry = routes.find((entry) => slugWithLocale === entry.slug);
+	const slug = item.slug === 'index' ? '' : item.slug;
+	const localizedSlug = locale ? (slug ? locale + '/' + slug : locale) : slug;
+	const entry = routes.find((entry) => localizedSlug === entry.slug);
 	if (!entry) {
 		const hasExternalSlashes = item.slug.at(0) === '/' || item.slug.at(-1) === '/';
 		if (hasExternalSlashes) {
@@ -410,4 +410,7 @@ function applyPrevNextLinkConfig(
 }
 
 /** Remove the extension from a path. */
-const stripExtension = (path: string) => path.replace(/\.\w+$/, '');
+function stripExtension(path: string) {
+	const periodIndex = path.lastIndexOf('.');
+	return path.slice(0, periodIndex > -1 ? periodIndex : undefined);
+}
diff --git a/packages/starlight/utils/slugs.ts b/packages/starlight/utils/slugs.ts
index 8a7cbd70ec..afe971ba3b 100644
--- a/packages/starlight/utils/slugs.ts
+++ b/packages/starlight/utils/slugs.ts
@@ -1,5 +1,6 @@
 import config from 'virtual:starlight/user-config';
 import { BuiltInDefaultLocale } from './i18n';
+import { stripTrailingSlash } from './path';
 
 export interface LocaleData {
 	/** Writing direction. */
@@ -52,7 +53,7 @@ export function slugToParam(slug: string): string | undefined {
 	return slug === 'index' || slug === ''
 		? undefined
 		: slug.endsWith('/index')
-			? slug.replace(/\/index$/, '')
+			? slug.slice(0, -6)
 			: slug;
 }
 
@@ -77,7 +78,7 @@ export function localizedSlug(slug: string, locale: string | undefined): string
 	locale = locale || '';
 	if (slugLocale === slug) return locale;
 	if (slugLocale) {
-		return slug.replace(slugLocale + '/', locale ? locale + '/' : '').replace(/\/$/, '');
+		return stripTrailingSlash(slug.replace(slugLocale + '/', locale ? locale + '/' : ''));
 	}
 	return slug ? locale + '/' + slug : locale;
 }
@@ -106,7 +107,7 @@ export function localizedId(id: string, locale: string | undefined): string {
 /** Extract the slug from a URL. */
 export function urlToSlug(url: URL): string {
 	let pathname = url.pathname;
-	const base = import.meta.env.BASE_URL.replace(/\/$/, '');
+	const base = stripTrailingSlash(import.meta.env.BASE_URL);
 	if (pathname.startsWith(base)) pathname = pathname.replace(base, '');
 	const segments = pathname.split('/');
 	const htmlExt = '.html';