diff --git a/AGENTS.md b/AGENTS.md
index 9bedb41..bea3bb7 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -162,9 +162,15 @@ not for the public pages. See `docs/design-principles.md` for the design.
 - Keep dependencies minimal; add via `uv add` and mention it.
 - The public URL space belongs to content (pretty slugs at root). Reserve
   only `/_/` for the machinery (files, API, built assets, admin), plus
-  `/favicon.ico` from the build. Slugs may not begin with `_` or `.` —
-  validated in the site editor, rejected by the API, and such URLs are
-  never looked up as content when serving.
+  `/favicon.ico` from the build. Slugs are lowercase ASCII `[a-z0-9-]`
+  (the site editor filters input live via `slugify.js`, built on the
+  `transliteration` npm package — unicode folds to ASCII, spaces become
+  hyphens; an empty slug on a new page is derived from its title), may
+  not begin with `_` or `.`, and may not be a reserved file name
+  (`robots.txt`, `ads.txt`, `sitemap.xml`, `openapi.json`, `favicon.ico`,
+  `site.webmanifest`). The API rejects such paths with a human-readable
+  reason shown in the editor, and such URLs are never looked up as
+  content when serving.
 - No auth in core code; trusted single author. Never add output
   sanitization "for safety" against the author — embedded HTML/scripts in
   Markdown are passed through deliberately.
diff --git a/docs/design-principles.md b/docs/design-principles.md
index 733003a..1fe147d 100644
--- a/docs/design-principles.md
+++ b/docs/design-principles.md
@@ -32,8 +32,11 @@ evolves.
   lives under `/_/` (the API at `/_/api/`, uploaded files at `/_/f/`, built
   assets at `/_/assets/`, and the admin shell at `/_/admin`). The only
   other reserved root path is `/favicon.ico`, served from the build.
-  Slugs may not begin with `_` or `.` anywhere in the path — such URLs
-  are never looked up as content.
+  Slugs are lowercase ASCII (`[a-z0-9-]`; input is transliterated and
+  filtered as you type, and a new page's empty slug is derived from its
+  title), may not begin with `_` or `.`, and may not occupy a reserved
+  root file name (`robots.txt`, `sitemap.xml`, `favicon.ico`, …) — such
+  URLs are never looked up as content.
 - **Single user, trusted author.** No auth concerns in the core design.
   Everything published is public; only editing tools will later sit behind
   access control (external SSO when that time comes). The author is trusted
diff --git a/frontend/package-lock.json b/frontend/package-lock.json
index 6910824..c70a586 100644
--- a/frontend/package-lock.json
+++ b/frontend/package-lock.json
@@ -14,6 +14,7 @@
         "@codemirror/view": "^6.43.8",
         "@lezer/highlight": "^1.2.3",
         "codemirror": "^6.0.2",
+        "transliteration": "^2.6.1",
         "vue": "^3.5.26",
         "vuedraggable": "^4.1.0"
       },
@@ -2528,6 +2529,19 @@
         "node": ">=6"
       }
     },
+    "node_modules/transliteration": {
+      "version": "2.6.1",
+      "resolved": "https://registry.npmjs.org/transliteration/-/transliteration-2.6.1.tgz",
+      "integrity": "sha512-hJ9BhrQAOnNTbpOr1MxsNjZISkn7ppvF5TKUeFmTE1mG4ZPD/XVxF0L0LUoIUCWmQyxH0gJpVtfYLAWf298U9w==",
+      "license": "MIT",
+      "bin": {
+        "slugify": "dist/bin/slugify",
+        "transliterate": "dist/bin/transliterate"
+      },
+      "engines": {
+        "node": ">=20.0.0"
+      }
+    },
     "node_modules/unplugin-utils": {
       "version": "0.3.2",
       "resolved": "https://registry.npmjs.org/unplugin-utils/-/unplugin-utils-0.3.2.tgz",
diff --git a/frontend/package.json b/frontend/package.json
index 9ba1f39..3054016 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -17,6 +17,7 @@
     "@codemirror/view": "^6.43.8",
     "@lezer/highlight": "^1.2.3",
     "codemirror": "^6.0.2",
+    "transliteration": "^2.6.1",
     "vue": "^3.5.26",
     "vuedraggable": "^4.1.0"
   },
diff --git a/frontend/src/SiteEditor.vue b/frontend/src/SiteEditor.vue
index d69a6c6..81e1e69 100644
--- a/frontend/src/SiteEditor.vue
+++ b/frontend/src/SiteEditor.vue
@@ -17,6 +17,7 @@ import { EditorState, Compartment } from '@codemirror/state'
 import { placeholder } from '@codemirror/view'
 import { html } from '@codemirror/lang-html'
 import { cmHighlight, cmTheme } from './cmtheme'
+import { slugify } from './slugify'
 
 const props = defineProps({
   pagePath: { type: String, default: '' },
@@ -196,14 +197,11 @@ function discardPending() {
 async function commitPending() {
   const node = pending.value
   if (!node) return
-  const slug = node.slug.trim().replace(/\/+/g, '')
+  // Empty slug: derive one from the title (transliterated to ASCII).
+  const slug = slugify(node.slug.trim()) || slugify(node.title)
   if (!slug) {
     return
   }
-  if (invalidSlug(slug)) {
-    saveError.value = '⚠️ slugs cannot begin with _ or .'
-    return // keep the pending row so the slug can be fixed
-  }
   const loc = locatePending(tree.value, '')
   const parentPath = loc?.parentPath ?? ''
   const newPath = parentPath ? `${parentPath}/${slug}` : slug
@@ -217,7 +215,9 @@ async function commitPending() {
     }),
   })
   if (!res.ok) {
-    saveError.value = '⚠️ changes could not be saved'
+    // Show the server's reason (e.g. a reserved file name); the pending
+    // row stays so it can be edited and committed again.
+    saveError.value = `⚠️ ${await errorDetail(res)}`
     return
   }
   // Place it exactly where the row was dropped: a fresh order key halfway
@@ -348,6 +348,13 @@ async function refreshPages() {
   } catch { /* list stays stale; not fatal */ }
 }
 
+// Human-readable reason from a failed API call (FastAPI errors carry a
+// JSON {detail}), falling back to a generic message.
+async function errorDetail(res) {
+  const body = await res.json().catch(() => null)
+  return body?.detail || 'changes could not be saved'
+}
+
 async function postStructure(op) {
   const res = await fetch('/_/api/structure', {
     method: 'POST',
@@ -358,7 +365,7 @@ async function postStructure(op) {
     saveError.value = ''
     loadPlain(path.value) // refresh menus and content from the server
   } else {
-    saveError.value = '⚠️ changes could not be saved'
+    saveError.value = `⚠️ ${await errorDetail(res)}`
   }
   await refreshPages()
   return res.ok
@@ -398,20 +405,11 @@ function onTitleInput(node, ev) {
   })
 }
 
-// Slugs may not begin with _ or . (reserved for the /_/ machinery and
-// dot-paths); enforced on every commit, and again server-side.
-function invalidSlug(slug) {
-  return slug.startsWith('_') || slug.startsWith('.')
-}
-
+// The slug inputs are filtered as you type (StructureTree onSlugInput,
+// see slugify.js); the server re-validates and its reason is shown.
 async function commitSlug(node, ev) {
-  const slug = ev.target.value.trim().replace(/\/+/g, '')
+  const slug = ev.target.value.trim()
   if (slug === node.slug) return
-  if (invalidSlug(slug)) {
-    saveError.value = '⚠️ slugs cannot begin with _ or .'
-    ev.target.value = node.slug
-    return
-  }
   const parent = node.path.split('/').slice(0, -1).join('/')
   // Empty slug at top level = the front page (path "").
   const moveTo = parent ? (slug ? `${parent}/${slug}` : parent) : slug
diff --git a/frontend/src/StructureTree.vue b/frontend/src/StructureTree.vue
index 9e70c11..de24fd3 100644
--- a/frontend/src/StructureTree.vue
+++ b/frontend/src/StructureTree.vue
@@ -17,6 +17,7 @@
 // forwarding.
 import { inject } from 'vue'
 import draggable from 'vuedraggable'
+import { slugify } from './slugify'
 
 defineOptions({ name: 'StructureTree' })
 const props = defineProps({
@@ -27,6 +28,18 @@ const props = defineProps({
 
 const handlers = inject('structureHandlers')
 
+// Live-filter the slug inputs as they are typed (oninput): invalid
+// characters are simply not accepted, spaces become hyphens and unicode
+// folds to ASCII (see slugify.js). Existing rows commit on change, the
+// pending row is v-modeled.
+function onSlugInput(ev) {
+  ev.target.value = slugify(ev.target.value)
+}
+
+function onPendingSlugInput(element, ev) {
+  element.slug = slugify(ev.target.value)
+}
+
 // Focus the title input of a fresh pending row.
 const vFocus = { mounted: (el) => el.focus() }
 
@@ -92,7 +105,8 @@ function onEnd() {
             <input
               v-model="element.slug"
               class="edit slug-edit"
-              placeholder="slug"
+              placeholder="slug — empty: derived from the title"
+              @input="onPendingSlugInput(element, $event)"
               @keyup.enter="handlers.commitPending()"
               @keyup.esc="handlers.discardPending()"
             />
@@ -115,6 +129,7 @@ function onEnd() {
               :value="element.slug"
               placeholder="front page"
               title="Slug (last path segment) — renames move the whole subtree. Empty at top level = front page"
+              @input="onSlugInput"
               @change="handlers.commitSlug(element, $event)"
             />
             <span class="acts">
diff --git a/frontend/src/slugify.js b/frontend/src/slugify.js
new file mode 100644
index 0000000..00fc129
--- /dev/null
+++ b/frontend/src/slugify.js
@@ -0,0 +1,10 @@
+// Slugs are URL path segments: lowercase ASCII letters, digits, hyphens.
+// The transliteration package folds unicode (incl. asian scripts) to
+// ASCII and spaces to hyphens; we then drop everything outside the slug
+// charset (including the reserved leading "_"/".", slashes, backslashes,
+// dots).
+import { slugify as transliterate } from 'transliteration'
+
+export function slugify(s) {
+  return transliterate(s).replace(/[^a-z0-9-]/g, '').replace(/-{2,}/g, '-')
+}
diff --git a/pagerite/app.py b/pagerite/app.py
index 6e35a13..502e435 100644
--- a/pagerite/app.py
+++ b/pagerite/app.py
@@ -349,10 +349,25 @@ def _is_reserved(path: str) -> bool:
     return any(seg.startswith(("_", ".")) for seg in path.split("/"))
 
 
+# Well-known root file names that content may not occupy (they would
+# shadow real files or carry special meaning to crawlers/clients).
+RESERVED_FILES = {
+    "robots.txt",
+    "ads.txt",
+    "sitemap.xml",
+    "openapi.json",
+    "favicon.ico",
+    "site.webmanifest",
+}
+
+
 def _check_reserved(path: str) -> None:
-    """Reject configured slugs beginning with "_" or "."."""
+    """Reject configured slugs beginning with "_" or ".", and reserved
+    file names at the root."""
     if _is_reserved(path):
         raise HTTPException(400, 'slugs cannot begin with "_" or "."')
+    if path in RESERVED_FILES:
+        raise HTTPException(400, f'"{path}" is a reserved file name')
 
 
 @app.websocket("/_/api/ws/editor")
@@ -497,8 +512,8 @@ async def show_page(request: Request, path: str) -> HTMLResponse | Response:
     first child page in menu order.
     """
     path = path.strip("/")
-    if path and _is_reserved(path):
-        # Reserved slug shape: never content — don't even look it up.
+    if path and (_is_reserved(path) or path in RESERVED_FILES):
+        # Reserved slug shape or file name: never content — no tree lookup.
         return HTMLResponse(views.render_not_found(data.menu, path, data.brand), 404)
     chain = resolve(data.menu, path)
     node = chain[-1] if chain else None