diff --git a/assets/js/SearchTagInputHelper.ts b/assets/js/SearchTagInputHelper.ts
new file mode 100644
index 00000000..c042a3b9
--- /dev/null
+++ b/assets/js/SearchTagInputHelper.ts
@@ -0,0 +1,15 @@
+export function normalizeSearchTagInput(rawValue: string) {
+  if (!rawValue) {
+    return ''
+  }
+
+  let value = rawValue.trim()
+
+  // Collapse one or more OR tokens (case-insensitive) into a comma — the OR-group delimiter
+  value = value.replace(/\s*(?:\bor\b(?:\s+)?)+\s*/gi, ',')
+
+  // Replace remaining spaces (within individual tag names) with underscores
+  value = value.replace(/\s/g, '_')
+
+  return value
+}
diff --git a/components/pages/home/SimpleSearch.vue b/components/pages/home/SimpleSearch.vue
index 63892f3a..c32d1b10 100644
--- a/components/pages/home/SimpleSearch.vue
+++ b/components/pages/home/SimpleSearch.vue
@@ -2,6 +2,7 @@
   import { CheckIcon, MagnifyingGlassIcon } from '@heroicons/vue/20/solid'
   import { watchDebounced } from '@vueuse/core'
   import { abbreviateNumber } from 'js-abbreviation-number'
+  import { normalizeSearchTagInput } from '~/assets/js/SearchTagInputHelper'
   import Tag from '~/assets/js/tag.dto'
 
   const props = defineProps<{
@@ -22,14 +23,9 @@
 
   // Change event
   function onComboboxInputChange(event: InputEvent) {
-    let value = (event.target as HTMLInputElement).value
+    const value = (event.target as HTMLInputElement).value
 
-    value = value.trim()
-
-    // Replace empty spaces with underscores
-    value = value.replace(/\s/g, '_')
-
-    searchQuery.value = value
+    searchQuery.value = normalizeSearchTagInput(value)
   }
 
   watchDebounced(searchQuery, (value) => onSearchChange(value), { debounce: 350 })
diff --git a/components/pages/posts/navigation/search/SearchMenu.vue b/components/pages/posts/navigation/search/SearchMenu.vue
index 37367efe..76c361e9 100644
--- a/components/pages/posts/navigation/search/SearchMenu.vue
+++ b/components/pages/posts/navigation/search/SearchMenu.vue
@@ -4,6 +4,7 @@
   import { watchDebounced } from '@vueuse/core'
   import { abbreviateNumber } from 'js-abbreviation-number'
   import { cloneDeep, unionWith } from 'es-toolkit'
+  import { normalizeSearchTagInput } from '~/assets/js/SearchTagInputHelper'
   import Tag from '~/assets/js/tag.dto'
   import SearchSelect from './SearchSelect.vue'
 
@@ -60,14 +61,9 @@
 
   // Change event
   function onComboboxInputChange(event: InputEvent) {
-    let value = (event.target as HTMLInputElement).value
+    const value = (event.target as HTMLInputElement).value
 
-    value = value.trim()
-
-    // Replace empty spaces with underscores
-    value = value.replace(/\s/g, '_')
-
-    searchQuery.value = value
+    searchQuery.value = normalizeSearchTagInput(value)
   }
 
   watchDebounced(searchQuery, (value) => onSearchChange(value), { debounce: 350 })
diff --git a/test/assets/search-tag-input-helper.test.ts b/test/assets/search-tag-input-helper.test.ts
new file mode 100644
index 00000000..d346ad57
--- /dev/null
+++ b/test/assets/search-tag-input-helper.test.ts
@@ -0,0 +1,30 @@
+import { describe, expect, it } from 'vitest'
+import { normalizeSearchTagInput } from '../../assets/js/SearchTagInputHelper'
+
+describe('normalizeSearchTagInput', () => {
+  it('maps typed OR separators to commas case-insensitively', () => {
+    expect(normalizeSearchTagInput('cat OR dog')).toBe('cat,dog')
+    expect(normalizeSearchTagInput('cat or dog')).toBe('cat,dog')
+    expect(normalizeSearchTagInput('cat Or dog')).toBe('cat,dog')
+    expect(normalizeSearchTagInput('cat oR dog')).toBe('cat,dog')
+  })
+
+  it('maps multiple OR separators to commas', () => {
+    expect(normalizeSearchTagInput('cat OR dog or fish')).toBe('cat,dog,fish')
+  })
+
+  it('preserves existing behavior of converting spaces in tags to underscores', () => {
+    expect(normalizeSearchTagInput('black hair')).toBe('black_hair')
+    expect(normalizeSearchTagInput('black hair OR blue eyes')).toBe('black_hair,blue_eyes')
+  })
+
+  it('trims surrounding whitespace', () => {
+    expect(normalizeSearchTagInput('  cat OR dog  ')).toBe('cat,dog')
+  })
+
+  it('collapses adjacent/repeated OR separators into a single comma', () => {
+    expect(normalizeSearchTagInput('cat OR OR dog')).toBe('cat,dog')
+    expect(normalizeSearchTagInput('cat or OR or dog')).toBe('cat,dog')
+    expect(normalizeSearchTagInput('cat OR OR OR dog')).toBe('cat,dog')
+  })
+})