diff --git a/src/main/i18n/locales/en_US/messages.json b/src/main/i18n/locales/en_US/messages.json
index 110ee554..2f716b2a 100644
--- a/src/main/i18n/locales/en_US/messages.json
+++ b/src/main/i18n/locales/en_US/messages.json
@@ -31,7 +31,12 @@
     ]
   },
   "error": {
-    "migration": "Auto-migration from SQLite failed: {{error}}"
+    "migration": "Auto-migration from SQLite failed: {{error}}",
+    "entryNameEmpty": "Name cannot be empty.",
+    "entryNameLeadingDot": "Name cannot start with a dot.",
+    "entryNameInvalidChars": "Name cannot contain these characters: {{- chars}}",
+    "entryNameTrailingDot": "Name cannot end with a dot.",
+    "entryNameWindowsReserved": "This name is reserved on Windows."
   },
   "description": {
     "storageVault": "Choose the vault directory. To sync between devices, select a folder in iCloud Drive, Google Drive or Dropbox.",
diff --git a/src/main/i18n/locales/ru_RU/messages.json b/src/main/i18n/locales/ru_RU/messages.json
index 74bc9b60..e1904068 100644
--- a/src/main/i18n/locales/ru_RU/messages.json
+++ b/src/main/i18n/locales/ru_RU/messages.json
@@ -26,7 +26,12 @@
     ]
   },
   "error": {
-    "migration": "Автомиграция из SQLite завершилась ошибкой: {{error}}"
+    "migration": "Автомиграция из SQLite завершилась ошибкой: {{error}}",
+    "entryNameEmpty": "Имя не может быть пустым.",
+    "entryNameLeadingDot": "Имя не может начинаться с точки.",
+    "entryNameInvalidChars": "Имя не может содержать эти символы: {{- chars}}",
+    "entryNameTrailingDot": "Имя не может заканчиваться точкой.",
+    "entryNameWindowsReserved": "Это имя зарезервировано в Windows."
   },
   "description": {
     "storageVault": "Выберите директорию для хранилища. Для синхронизации между устройствами выберите папку в iCloud Drive, Google Drive или Dropbox.",
diff --git a/src/main/storage/providers/markdown/runtime/__tests__/validation.test.ts b/src/main/storage/providers/markdown/runtime/__tests__/validation.test.ts
new file mode 100644
index 00000000..d5ad7989
--- /dev/null
+++ b/src/main/storage/providers/markdown/runtime/__tests__/validation.test.ts
@@ -0,0 +1,24 @@
+import { validateEntryName } from '../validation'
+
+describe('validateEntryName', () => {
+  it('rejects names starting with dot', () => {
+    expect(() => validateEntryName('.note', 'note')).toThrow(
+      'INVALID_NAME:note name cannot start with a dot',
+    )
+    expect(() => validateEntryName('.snippet', 'snippet')).toThrow(
+      'INVALID_NAME:snippet name cannot start with a dot',
+    )
+  })
+
+  it('rejects names with Obsidian-reserved characters', () => {
+    expect(() => validateEntryName('note#heading', 'note')).toThrow(
+      'INVALID_NAME:note name contains invalid characters',
+    )
+    expect(() => validateEntryName('folder[name]', 'folder')).toThrow(
+      'INVALID_NAME:folder name contains invalid characters',
+    )
+    expect(() => validateEntryName('snippet^block', 'snippet')).toThrow(
+      'INVALID_NAME:snippet name contains invalid characters',
+    )
+  })
+})
diff --git a/src/main/storage/providers/markdown/runtime/constants.ts b/src/main/storage/providers/markdown/runtime/constants.ts
index e44344b0..2c32a354 100644
--- a/src/main/storage/providers/markdown/runtime/constants.ts
+++ b/src/main/storage/providers/markdown/runtime/constants.ts
@@ -33,12 +33,16 @@ export const SEARCH_WORD_RE = /[\p{L}\p{N}_]+/gu
 export const STATE_WRITE_DEBOUNCE_MS = 100
 export const INVALID_NAME_CHARS_RE = /[<>:"/\\|?*]/g
 export const INVALID_NAME_CHARS = new Set([
+  '#',
   '<',
   '>',
   ':',
   '"',
   '/',
   '\\',
+  '[',
+  ']',
+  '^',
   '|',
   '?',
   '*',
diff --git a/src/main/storage/providers/markdown/runtime/validation.ts b/src/main/storage/providers/markdown/runtime/validation.ts
index 3aa72e47..7d85c28b 100644
--- a/src/main/storage/providers/markdown/runtime/validation.ts
+++ b/src/main/storage/providers/markdown/runtime/validation.ts
@@ -49,6 +49,10 @@ export function validateEntryName(
     throwStorageError('INVALID_NAME', `${kind} name is empty or invalid`)
   }
 
+  if (normalized.startsWith('.')) {
+    throwStorageError('INVALID_NAME', `${kind} name cannot start with a dot`)
+  }
+
   if (hasInvalidNameChars(normalized)) {
     throwStorageError(
       'INVALID_NAME',
diff --git a/src/renderer/components/editor/header/Header.vue b/src/renderer/components/editor/header/Header.vue
index 354ea5d4..2580b514 100644
--- a/src/renderer/components/editor/header/Header.vue
+++ b/src/renderer/components/editor/header/Header.vue
@@ -8,7 +8,6 @@ import {
 } from '@/composables'
 import { i18n } from '@/electron'
 import { navigateBack, navigateForward } from '@/ipc/listeners/deepLinks'
-
 import {
   ChevronLeft,
   ChevronRight,
@@ -20,6 +19,10 @@ import {
   Plus,
   Type,
 } from 'lucide-vue-next'
+import {
+  formatEntryNameValidationChars,
+  getEntryNameValidationIssue,
+} from '~/shared/entryNameValidation'
 
 const {
   selectedSnippet,
@@ -39,14 +42,20 @@ const {
 const { addToUpdateQueue } = useSnippetUpdate()
 
 const isShowDescription = ref(false)
+const isNameFocused = ref(false)
 
 const {
   model: name,
   onFocus: onNameFocus,
   onBlur,
+  reset: resetName,
 } = useEditableField(
   () => selectedSnippet?.value?.name,
   (v) => {
+    if (getEntryNameValidationIssue(v)) {
+      return
+    }
+
     addToUpdateQueue(selectedSnippet.value!.id, {
       name: v,
       description: selectedSnippet.value!.description,
@@ -57,7 +66,52 @@ const {
   },
 )
 
+const nameValidationIssue = computed(() =>
+  getEntryNameValidationIssue(name.value),
+)
+const nameValidationMessage = computed(() => {
+  const issue = nameValidationIssue.value
+
+  if (!issue) {
+    return ''
+  }
+
+  if (issue.code === 'invalidChars') {
+    return i18n.t('messages:error.entryNameInvalidChars', {
+      chars: formatEntryNameValidationChars(issue.chars),
+    })
+  }
+
+  if (issue.code === 'leadingDot') {
+    return i18n.t('messages:error.entryNameLeadingDot')
+  }
+
+  if (issue.code === 'trailingDot') {
+    return i18n.t('messages:error.entryNameTrailingDot')
+  }
+
+  if (issue.code === 'windowsReserved') {
+    return i18n.t('messages:error.entryNameWindowsReserved')
+  }
+
+  return i18n.t('messages:error.entryNameEmpty')
+})
+
+const isNameValidationTooltipOpen = computed(() => {
+  return isNameFocused.value && Boolean(nameValidationMessage.value)
+})
+
+function onSnippetNameFocus() {
+  isNameFocused.value = true
+  onNameFocus()
+}
+
 function onNameBlur() {
+  if (nameValidationIssue.value) {
+    resetName()
+  }
+
+  isNameFocused.value = false
   onBlur()
   isFocusedSnippetName.value = false
 }
@@ -129,14 +183,19 @@ function onJsonVisualizerToggle() {
           </UiActionButton>
         </div>
         <div class="min-w-0 flex-1">
-          <UiInput
-            v-model="name"
-            variant="ghost"
-            class="w-full truncate px-0"
-            :select="isFocusedSnippetName"
-            @focus="onNameFocus"
-            @blur="onNameBlur"
-          />
+          <UiInputValidationTooltip
+            :open="isNameValidationTooltipOpen"
+            :message="nameValidationMessage"
+          >
+            <UiInput
+              v-model="name"
+              variant="ghost"
+              class="w-full truncate px-0"
+              :select="isFocusedSnippetName"
+              @focus="onSnippetNameFocus"
+              @blur="onNameBlur"
+            />
+          </UiInputValidationTooltip>
         </div>
       </div>
       <div class="ml-2 flex">
diff --git a/src/renderer/components/notes/NotesEditorPane.vue b/src/renderer/components/notes/NotesEditorPane.vue
index 641838d1..dbc1b581 100644
--- a/src/renderer/components/notes/NotesEditorPane.vue
+++ b/src/renderer/components/notes/NotesEditorPane.vue
@@ -22,6 +22,10 @@ import {
   Pencil,
   Presentation,
 } from 'lucide-vue-next'
+import {
+  formatEntryNameValidationChars,
+  getEntryNameValidationIssue,
+} from '~/shared/entryNameValidation'
 import { shouldSyncSelectedNoteContent } from './editorSync'
 import { getTextStats } from './textStats'
 
@@ -61,6 +65,7 @@ const presentationActionTooltip = computed(() =>
     : i18n.t('menu:markdown.presentationMode'),
 )
 const isHistoryVisible = computed(() => canGoBack.value || canGoForward.value)
+const isNameFocused = ref(false)
 
 function onSidebarToggle() {
   toggleNotesSidebar()
@@ -98,16 +103,66 @@ const {
   model: name,
   onFocus: onNameFocus,
   onBlur,
+  reset: resetName,
 } = useEditableField(
   () => selectedNote.value?.name,
   (v) => {
+    if (getEntryNameValidationIssue(v)) {
+      return
+    }
+
     if (selectedNote.value) {
       addToUpdateQueue(selectedNote.value.id, { name: v })
     }
   },
 )
 
+const nameValidationIssue = computed(() =>
+  getEntryNameValidationIssue(name.value),
+)
+const nameValidationMessage = computed(() => {
+  const issue = nameValidationIssue.value
+
+  if (!issue) {
+    return ''
+  }
+
+  if (issue.code === 'invalidChars') {
+    return i18n.t('messages:error.entryNameInvalidChars', {
+      chars: formatEntryNameValidationChars(issue.chars),
+    })
+  }
+
+  if (issue.code === 'leadingDot') {
+    return i18n.t('messages:error.entryNameLeadingDot')
+  }
+
+  if (issue.code === 'trailingDot') {
+    return i18n.t('messages:error.entryNameTrailingDot')
+  }
+
+  if (issue.code === 'windowsReserved') {
+    return i18n.t('messages:error.entryNameWindowsReserved')
+  }
+
+  return i18n.t('messages:error.entryNameEmpty')
+})
+
+const isNameValidationTooltipOpen = computed(() => {
+  return isNameFocused.value && Boolean(nameValidationMessage.value)
+})
+
+function onNoteNameFocus() {
+  isNameFocused.value = true
+  onNameFocus()
+}
+
 function onNameBlur() {
+  if (nameValidationIssue.value) {
+    resetName()
+  }
+
+  isNameFocused.value = false
   onBlur()
   isFocusedNoteName.value = false
 }
@@ -170,14 +225,19 @@ const textStats = computed(() => getTextStats(content.value))
             </UiActionButton>
           </div>
           <div class="min-w-0 flex-1">
-            <UiInput
-              v-model="name"
-              variant="ghost"
-              class="w-full truncate px-0"
-              :select="isFocusedNoteName"
-              @focus="onNameFocus"
-              @blur="onNameBlur"
-            />
+            <UiInputValidationTooltip
+              :open="isNameValidationTooltipOpen"
+              :message="nameValidationMessage"
+            >
+              <UiInput
+                v-model="name"
+                variant="ghost"
+                class="w-full truncate px-0"
+                :select="isFocusedNoteName"
+                @focus="onNoteNameFocus"
+                @blur="onNameBlur"
+              />
+            </UiInputValidationTooltip>
           </div>
         </div>
         <div class="ml-2 flex h-7 items-center">
diff --git a/src/renderer/components/notes/NotesSidebarFolders.vue b/src/renderer/components/notes/NotesSidebarFolders.vue
index d8bfaed2..1334cce0 100644
--- a/src/renderer/components/notes/NotesSidebarFolders.vue
+++ b/src/renderer/components/notes/NotesSidebarFolders.vue
@@ -12,6 +12,7 @@ import {
 } from '@/composables'
 import { i18n, store } from '@/electron'
 import { router, RouterName } from '@/router'
+import { getEntryNameValidationMessage } from '@/utils'
 import { Folder, Plus } from 'lucide-vue-next'
 import { useRoute } from 'vue-router'
 import { LAYOUT_DEFAULTS } from '~/main/store/constants'
@@ -114,6 +115,10 @@ const highlightedIds = computed({
 
 const contextNode = ref<any>(null)
 
+function getFolderValidationMessage(_node: TreeNodeType, value: string) {
+  return getEntryNameValidationMessage(value, i18n.t.bind(i18n))
+}
+
 // --- Event handlers ---
 
 async function onClickNode({
@@ -220,6 +225,7 @@ function onCancelEdit() {
               :editable-id="editableId"
               :focused-id="focusedId"
               :highlighted-ids="highlightedIds"
+              :get-validation-message="getFolderValidationMessage"
               class="h-full px-0.5 pb-1"
               @click-node="onClickNode"
               @dblclick-node="onDblclickNode"
diff --git a/src/renderer/components/sidebar/folders/Tree.vue b/src/renderer/components/sidebar/folders/Tree.vue
index 4a3e1263..294b65db 100644
--- a/src/renderer/components/sidebar/folders/Tree.vue
+++ b/src/renderer/components/sidebar/folders/Tree.vue
@@ -6,7 +6,7 @@ import * as ContextMenu from '@/components/ui/shadcn/context-menu'
 import { Tree as UiTree } from '@/components/ui/tree'
 import { useApp, useDialog, useFolders, useSnippets } from '@/composables'
 import { i18n } from '@/electron'
-import { scrollToElement } from '@/utils'
+import { getEntryNameValidationMessage, scrollToElement } from '@/utils'
 import { Folder } from 'lucide-vue-next'
 import CustomIcons from './custom-icons/CustomIcons.vue'
 
@@ -111,6 +111,10 @@ const contextNodeDefaultLanguage = computed(() => {
   )
 })
 
+function getFolderValidationMessage(_node: TreeNodeType, value: string) {
+  return getEntryNameValidationMessage(value, i18n.t.bind(i18n))
+}
+
 // --- Event handlers ---
 
 function onClickNode({
@@ -324,6 +328,7 @@ async function onRemoveCustomIcon() {
           :editable-id="editableId"
           :focused-id="focusedId"
           :highlighted-ids="highlightedIds"
+          :get-validation-message="getFolderValidationMessage"
           @click-node="onClickNode"
           @dblclick-node="onDblclickNode"
           @toggle-node="onToggleNode"
diff --git a/src/renderer/components/ui/input/ValidationTooltip.vue b/src/renderer/components/ui/input/ValidationTooltip.vue
new file mode 100644
index 00000000..b65e9e05
--- /dev/null
+++ b/src/renderer/components/ui/input/ValidationTooltip.vue
@@ -0,0 +1,36 @@
+<script setup lang="ts">
+import * as Popover from '@/components/ui/shadcn/popover'
+import { CircleAlert } from 'lucide-vue-next'
+
+interface Props {
+  message?: string
+  open?: boolean
+}
+
+defineProps<Props>()
+</script>
+
+<template>
+  <Popover.Popover
+    :open="open && Boolean(message)"
+    :modal="false"
+  >
+    <Popover.PopoverAnchor as-child>
+      <slot />
+    </Popover.PopoverAnchor>
+    <Popover.PopoverContent
+      v-if="message"
+      side="bottom"
+      align="start"
+      :side-offset="8"
+      class="border-destructive/30 bg-popover text-popover-foreground ring-destructive/10 w-fit max-w-80 px-3 py-2 shadow-md ring-1"
+    >
+      <div class="flex items-start gap-2">
+        <CircleAlert class="text-destructive mt-0.5 size-4 shrink-0" />
+        <p class="text-sm leading-5">
+          {{ message }}
+        </p>
+      </div>
+    </Popover.PopoverContent>
+  </Popover.Popover>
+</template>
diff --git a/src/renderer/components/ui/tree/Tree.vue b/src/renderer/components/ui/tree/Tree.vue
index 4f3022ec..d229d645 100644
--- a/src/renderer/components/ui/tree/Tree.vue
+++ b/src/renderer/components/ui/tree/Tree.vue
@@ -10,6 +10,7 @@ interface Props {
   focusedId?: string | number | undefined
   highlightedIds?: Set<string | number>
   indent?: number
+  getValidationMessage?: (node: TreeNode, value: string) => string
 }
 
 interface Emits {
@@ -142,6 +143,7 @@ provide(treeInjectionKey, {
   contextMenu,
   updateLabel: updateLabelHandler,
   cancelEdit: cancelEditHandler,
+  getValidationMessage: props.getValidationMessage,
   isHoveredByIdDisabled,
   editableId: internalEditableId,
   selectedIds: internalSelectedIds,
diff --git a/src/renderer/components/ui/tree/TreeNode.vue b/src/renderer/components/ui/tree/TreeNode.vue
index 8a1e55eb..5ce632f4 100644
--- a/src/renderer/components/ui/tree/TreeNode.vue
+++ b/src/renderer/components/ui/tree/TreeNode.vue
@@ -37,6 +37,7 @@ const {
   contextMenu,
   updateLabel,
   cancelEdit,
+  getValidationMessage,
   editableId,
   selectedIds,
   focusedId,
@@ -78,6 +79,9 @@ const isFocused = computed(() => focusedId.value === props.node.id)
 const isHighlighted = computed(() => highlightedIds.value.has(props.node.id))
 
 const isEditing = computed(() => editableId.value === props.node.id)
+const validationMessage = computed(() => {
+  return getValidationMessage?.(props.node, editValue.value) || ''
+})
 
 const isDragActive = computed(() => Boolean(dragStore.dragNode))
 
@@ -357,9 +361,13 @@ function onDrop(e: DragEvent) {
 
 // --- Inline Edit ---
 
-function onUpdateLabel() {
+function submitEdit() {
   const trimmed = editValue.value.trim()
 
+  if (validationMessage.value) {
+    return
+  }
+
   if (trimmed === '' || editValue.value === props.node.label) {
     editValue.value = props.node.label
     cancelEdit(props.node)
@@ -369,6 +377,15 @@ function onUpdateLabel() {
   updateLabel(props.node, editValue.value)
 }
 
+function onBlurEdit() {
+  if (validationMessage.value) {
+    onCancelEdit()
+    return
+  }
+
+  submitEdit()
+}
+
 function onCancelEdit() {
   editValue.value = props.node.label
   cancelEdit(props.node)
@@ -438,16 +455,21 @@ function onCancelEdit() {
             {{ node.label }}
           </span>
         </template>
-        <input
+        <UiInputValidationTooltip
           v-else
-          ref="editInputRef"
-          v-model="editValue"
-          class="outline-primary mr-1 min-w-0 flex-1 rounded-sm bg-transparent outline outline-1"
-          @keydown.esc="onCancelEdit"
-          @keydown.enter="onUpdateLabel"
-          @blur="onUpdateLabel"
-          @click.stop
+          :open="Boolean(validationMessage)"
+          :message="validationMessage"
         >
+          <input
+            ref="editInputRef"
+            v-model="editValue"
+            class="outline-primary mr-1 min-w-0 flex-1 rounded-sm bg-transparent outline outline-1"
+            @keydown.esc="onCancelEdit"
+            @keydown.enter="submitEdit"
+            @blur="onBlurEdit"
+            @click.stop
+          >
+        </UiInputValidationTooltip>
       </span>
     </div>
     <template v-if="node.children">
diff --git a/src/renderer/components/ui/tree/keys.ts b/src/renderer/components/ui/tree/keys.ts
index 48140c54..d6742eb5 100644
--- a/src/renderer/components/ui/tree/keys.ts
+++ b/src/renderer/components/ui/tree/keys.ts
@@ -18,6 +18,7 @@ export interface TreeInjection {
   contextMenu: (node: TreeNode) => void
   updateLabel: (node: TreeNode, value: string) => void
   cancelEdit: (node: TreeNode) => void
+  getValidationMessage?: (node: TreeNode, value: string) => string
   isHoveredByIdDisabled: Ref<boolean>
   editableId: Ref<string | number | null>
   selectedIds: Ref<(string | number)[]>
diff --git a/src/renderer/composables/useEditableField.ts b/src/renderer/composables/useEditableField.ts
index 822f555a..8b61017f 100644
--- a/src/renderer/composables/useEditableField.ts
+++ b/src/renderer/composables/useEditableField.ts
@@ -33,5 +33,9 @@ export function useEditableField(
     isFocused.value = false
   }
 
-  return { model, onFocus, onBlur }
+  function reset() {
+    localValue.value = source() ?? ''
+  }
+
+  return { model, onFocus, onBlur, reset }
 }
diff --git a/src/renderer/utils/__tests__/entryNameValidationMessage.test.ts b/src/renderer/utils/__tests__/entryNameValidationMessage.test.ts
new file mode 100644
index 00000000..a2c7dcb4
--- /dev/null
+++ b/src/renderer/utils/__tests__/entryNameValidationMessage.test.ts
@@ -0,0 +1,35 @@
+import { getEntryNameValidationMessage } from '../entryNameValidationMessage'
+
+describe('getEntryNameValidationMessage', () => {
+  const t = (key: string, params?: Record<string, unknown>) => {
+    if (key === 'messages:error.entryNameLeadingDot') {
+      return 'leading dot'
+    }
+
+    if (key === 'messages:error.entryNameTrailingDot') {
+      return 'trailing dot'
+    }
+
+    if (key === 'messages:error.entryNameWindowsReserved') {
+      return 'windows reserved'
+    }
+
+    if (key === 'messages:error.entryNameEmpty') {
+      return 'empty'
+    }
+
+    if (key === 'messages:error.entryNameInvalidChars') {
+      return `invalid ${(params?.chars as string) || ''}`.trim()
+    }
+
+    return key
+  }
+
+  it('returns leading dot message', () => {
+    expect(getEntryNameValidationMessage('.folder', t)).toBe('leading dot')
+  })
+
+  it('returns invalid chars message with raw characters', () => {
+    expect(getEntryNameValidationMessage('bad<name', t)).toBe('invalid <')
+  })
+})
diff --git a/src/renderer/utils/entryNameValidationMessage.ts b/src/renderer/utils/entryNameValidationMessage.ts
new file mode 100644
index 00000000..307d66d1
--- /dev/null
+++ b/src/renderer/utils/entryNameValidationMessage.ts
@@ -0,0 +1,37 @@
+import {
+  formatEntryNameValidationChars,
+  getEntryNameValidationIssue,
+} from '~/shared/entryNameValidation'
+
+type TranslateFn = (key: string, params?: Record<string, unknown>) => string
+
+export function getEntryNameValidationMessage(
+  name: string,
+  translate: TranslateFn,
+): string {
+  const issue = getEntryNameValidationIssue(name)
+
+  if (!issue) {
+    return ''
+  }
+
+  if (issue.code === 'invalidChars') {
+    return translate('messages:error.entryNameInvalidChars', {
+      chars: formatEntryNameValidationChars(issue.chars),
+    })
+  }
+
+  if (issue.code === 'leadingDot') {
+    return translate('messages:error.entryNameLeadingDot')
+  }
+
+  if (issue.code === 'trailingDot') {
+    return translate('messages:error.entryNameTrailingDot')
+  }
+
+  if (issue.code === 'windowsReserved') {
+    return translate('messages:error.entryNameWindowsReserved')
+  }
+
+  return translate('messages:error.entryNameEmpty')
+}
diff --git a/src/renderer/utils/index.ts b/src/renderer/utils/index.ts
index e623fd04..9b1d2c17 100644
--- a/src/renderer/utils/index.ts
+++ b/src/renderer/utils/index.ts
@@ -40,3 +40,5 @@ export function getContiguousSelection(
 
   return orderedIds.slice(startIndex, endIndex + 1)
 }
+
+export * from './entryNameValidationMessage'
diff --git a/src/shared/__tests__/entryNameValidation.test.ts b/src/shared/__tests__/entryNameValidation.test.ts
new file mode 100644
index 00000000..8a1d57c1
--- /dev/null
+++ b/src/shared/__tests__/entryNameValidation.test.ts
@@ -0,0 +1,57 @@
+import {
+  findInvalidEntryNameChars,
+  formatEntryNameValidationChars,
+  getEntryNameValidationIssue,
+} from '../entryNameValidation'
+
+describe('entryNameValidation', () => {
+  it('collects unique invalid characters in input order', () => {
+    expect(findInvalidEntryNameChars('bad:/name:*')).toEqual([':', '/', '*'])
+  })
+
+  it('returns invalid chars issue with collected characters', () => {
+    expect(getEntryNameValidationIssue('bad:/name')).toEqual({
+      code: 'invalidChars',
+      chars: [':', '/'],
+    })
+    expect(getEntryNameValidationIssue('bad#[name]^')).toEqual({
+      code: 'invalidChars',
+      chars: ['#', '[', ']', '^'],
+    })
+  })
+
+  it('returns empty issue for blank names', () => {
+    expect(getEntryNameValidationIssue('   ')).toEqual({
+      code: 'empty',
+    })
+  })
+
+  it('returns trailing issue for names ending with dot', () => {
+    expect(getEntryNameValidationIssue('note.')).toEqual({
+      code: 'trailingDot',
+    })
+  })
+
+  it('returns leading dot issue for names starting with dot', () => {
+    expect(getEntryNameValidationIssue('.note')).toEqual({
+      code: 'leadingDot',
+    })
+  })
+
+  it('returns reserved issue for Windows reserved names', () => {
+    expect(getEntryNameValidationIssue('con')).toEqual({
+      code: 'windowsReserved',
+    })
+    expect(getEntryNameValidationIssue('LPT1.txt')).toEqual({
+      code: 'windowsReserved',
+    })
+  })
+
+  it('returns null for valid names', () => {
+    expect(getEntryNameValidationIssue('Valid note name')).toBeNull()
+  })
+
+  it('formats control characters for tooltip display', () => {
+    expect(formatEntryNameValidationChars([':', '\n'])).toBe(': U+000A')
+  })
+})
diff --git a/src/shared/entryNameValidation.ts b/src/shared/entryNameValidation.ts
new file mode 100644
index 00000000..26f44eed
--- /dev/null
+++ b/src/shared/entryNameValidation.ts
@@ -0,0 +1,93 @@
+export type EntryNameValidationIssue =
+  | { code: 'empty' }
+  | { code: 'leadingDot' }
+  | { code: 'invalidChars', chars: string[] }
+  | { code: 'trailingDot' }
+  | { code: 'windowsReserved' }
+
+const INVALID_ENTRY_NAME_CHARS = new Set([
+  '#',
+  '<',
+  '>',
+  ':',
+  '"',
+  '/',
+  '\\',
+  '[',
+  ']',
+  '^',
+  '|',
+  '?',
+  '*',
+])
+
+const WINDOWS_RESERVED_NAME_RE
+  = /^(?:con|prn|aux|nul|com[1-9]|lpt[1-9])(?:\..*)?$/i
+
+function normalizeEntryName(name: string): string {
+  return name.trim()
+}
+
+export function findInvalidEntryNameChars(name: string): string[] {
+  const chars: string[] = []
+  const seen = new Set<string>()
+
+  for (const char of name) {
+    const isInvalid
+      = INVALID_ENTRY_NAME_CHARS.has(char) || char.charCodeAt(0) <= 0x1F
+
+    if (!isInvalid || seen.has(char)) {
+      continue
+    }
+
+    seen.add(char)
+    chars.push(char)
+  }
+
+  return chars
+}
+
+export function formatEntryNameValidationChars(chars: string[]): string {
+  return chars
+    .map((char) => {
+      if (char.charCodeAt(0) <= 0x1F) {
+        return `U+${char.charCodeAt(0).toString(16).padStart(4, '0').toUpperCase()}`
+      }
+
+      return char
+    })
+    .join(' ')
+}
+
+export function getEntryNameValidationIssue(
+  name: string,
+): EntryNameValidationIssue | null {
+  const normalizedName = normalizeEntryName(name)
+
+  if (!normalizedName || normalizedName === '.' || normalizedName === '..') {
+    return { code: 'empty' }
+  }
+
+  if (normalizedName.startsWith('.')) {
+    return { code: 'leadingDot' }
+  }
+
+  const invalidChars = findInvalidEntryNameChars(normalizedName)
+
+  if (invalidChars.length) {
+    return {
+      code: 'invalidChars',
+      chars: invalidChars,
+    }
+  }
+
+  if (normalizedName.endsWith('.')) {
+    return { code: 'trailingDot' }
+  }
+
+  if (WINDOWS_RESERVED_NAME_RE.test(normalizedName)) {
+    return { code: 'windowsReserved' }
+  }
+
+  return null
+}