diff --git a/src/booru/dto/booru-queries.dto.spec.ts b/src/booru/dto/booru-queries.dto.spec.ts
new file mode 100644
index 0000000..9722383
--- /dev/null
+++ b/src/booru/dto/booru-queries.dto.spec.ts
@@ -0,0 +1,79 @@
+import { BadRequestException } from '@nestjs/common'
+import { plainToInstance } from 'class-transformer'
+import { booruQueryValuesPostsDTO } from './booru-queries.dto'
+
+describe('booruQueryValuesPostsDTO', () => {
+  describe('tags transform', () => {
+    it('should decode URL-encoded ampersands in tags', () => {
+      const dto = plainToInstance(booruQueryValuesPostsDTO, {
+        tags: 'panty_%26_stocking_with_garterbelt'
+      })
+
+      expect(dto.tags).toEqual(['panty_&_stocking_with_garterbelt'])
+    })
+
+    it('should split pipe-separated tags and decode each one', () => {
+      const dto = plainToInstance(booruQueryValuesPostsDTO, {
+        tags: 'panty_%26_stocking_with_garterbelt|rating%3Asafe'
+      })
+
+      expect(dto.tags).toEqual(['panty_&_stocking_with_garterbelt', 'rating:safe'])
+    })
+
+    it('should normalize array tag inputs and keep tag array shape', () => {
+      const dto = plainToInstance(booruQueryValuesPostsDTO, {
+        tags: ['panty_%26_stocking_with_garterbelt|rating%3Asafe', 'score%3A%3E100']
+      })
+
+      expect(dto.tags).toEqual([
+        'panty_&_stocking_with_garterbelt',
+        'rating:safe',
+        'score:>100'
+      ])
+    })
+
+    it('should normalize non-string tag input without throwing', () => {
+      const dto = plainToInstance(booruQueryValuesPostsDTO, {
+        tags: 123
+      })
+
+      expect(dto.tags).toEqual(['123'])
+    })
+
+    it('should keep non-encoded percent tags unchanged', () => {
+      const dto = plainToInstance(booruQueryValuesPostsDTO, {
+        tags: '100%_real'
+      })
+
+      expect(dto.tags).toEqual(['100%_real'])
+    })
+
+    it('should throw BadRequestException when encoded tag decoding fails', () => {
+      expect(() =>
+        plainToInstance(booruQueryValuesPostsDTO, {
+          tags: 'bad%25%'
+        })
+      ).toThrow(BadRequestException)
+
+      expect(() =>
+        plainToInstance(booruQueryValuesPostsDTO, {
+          tags: 'bad%25%'
+        })
+      ).toThrow('Invalid tag encoding')
+    })
+
+    it('should return undefined when tags is undefined', () => {
+      const dto = plainToInstance(booruQueryValuesPostsDTO, {})
+
+      expect(dto.tags).toBeUndefined()
+    })
+
+    it('should return null when tags is null', () => {
+      const dto = plainToInstance(booruQueryValuesPostsDTO, {
+        tags: null
+      })
+
+      expect(dto.tags).toBeNull()
+    })
+  })
+})
\ No newline at end of file
diff --git a/src/booru/dto/booru-queries.dto.ts b/src/booru/dto/booru-queries.dto.ts
index 4a4bd12..3acc88e 100644
--- a/src/booru/dto/booru-queries.dto.ts
+++ b/src/booru/dto/booru-queries.dto.ts
@@ -18,6 +18,7 @@ import {
   Min
 } from 'class-validator'
 import { Transform } from 'class-transformer'
+import { BadRequestException } from '@nestjs/common'
 
 abstract class booruEndpointsDTO {
   @IsFQDN()
@@ -180,7 +181,26 @@ export class booruQueryValuesPostsDTO extends booruQueriesDTO {
   @IsArray()
   @ArrayNotEmpty()
   @ArrayNotContains([''])
-  @Transform(({ value }) => value.trim().split('|'))
+  @Transform(({ value }) => {
+    if (value === undefined || value === null) {
+      return value
+    }
+
+    return (Array.isArray(value) ? value : [value])
+      .map((tag) => (typeof tag === 'string' ? tag : String(tag)))
+      .flatMap((tag) => tag.trim().split('|'))
+      .map((tag) => {
+        if (!/%[0-9A-Fa-f]{2}/.test(tag)) {
+          return tag
+        }
+
+        try {
+          return decodeURIComponent(tag)
+        } catch {
+          throw new BadRequestException('Invalid tag encoding')
+        }
+      })
+  })
   @IsOptional()
   readonly tags: IBooruQueryValues['posts']['tags']