diff --git a/.prettierignore b/.prettierignore
new file mode 100644
index 0000000..f0aa14a
--- /dev/null
+++ b/.prettierignore
@@ -0,0 +1,5 @@
+# Ignore artifacts:
+package-lock.json
+dist
+build
+coverage
diff --git a/.prettierrc b/.prettierrc
new file mode 100644
index 0000000..ba4e1a9
--- /dev/null
+++ b/.prettierrc
@@ -0,0 +1,5 @@
+{
+  "semi": false,
+  "singleQuote": true
+}
+
diff --git a/package-lock.json b/package-lock.json
index d7c7a02..e248e3a 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -11,6 +11,7 @@
       "devDependencies": {
         "@vitest/coverage-v8": "^3.2.4",
         "esbuild": "^0.25.8",
+        "prettier": "^3.6.2",
         "rollup": "^4.46.2",
         "rollup-plugin-dts": "^6.2.1",
         "vitest": "^3.2.4"
@@ -1718,6 +1719,22 @@
         "node": "^10 || ^12 || >=14"
       }
     },
+    "node_modules/prettier": {
+      "version": "3.6.2",
+      "resolved": "https://registry.npmjs.org/prettier/-/prettier-3.6.2.tgz",
+      "integrity": "sha512-I7AIg5boAr5R0FFtJ6rCfD+LFsWHp81dolrFD8S79U9tb8Az2nGrJncnMSnys+bpQJfRUzqs9hnA81OAA3hCuQ==",
+      "dev": true,
+      "license": "MIT",
+      "bin": {
+        "prettier": "bin/prettier.cjs"
+      },
+      "engines": {
+        "node": ">=14"
+      },
+      "funding": {
+        "url": "https://github.com/prettier/prettier?sponsor=1"
+      }
+    },
     "node_modules/rollup": {
       "version": "4.46.2",
       "resolved": "https://registry.npmjs.org/rollup/-/rollup-4.46.2.tgz",
diff --git a/package.json b/package.json
index f7e4446..a0bc308 100644
--- a/package.json
+++ b/package.json
@@ -16,11 +16,13 @@
   "scripts": {
     "build": "npx esbuild src/index.js --bundle --minify --outfile=dist/index.js --format=esm && npx rollup -c",
     "test": "vitest",
-    "cover": "vitest --coverage"
+    "cover": "vitest --coverage",
+    "format": "prettier . --write"
   },
   "devDependencies": {
     "@vitest/coverage-v8": "^3.2.4",
     "esbuild": "^0.25.8",
+    "prettier": "^3.6.2",
     "rollup": "^4.46.2",
     "rollup-plugin-dts": "^6.2.1",
     "vitest": "^3.2.4"
diff --git a/src/ConstArray.js b/src/ConstArray.js
index 3008616..d29d030 100644
--- a/src/ConstArray.js
+++ b/src/ConstArray.js
@@ -1,4 +1,4 @@
-import { parse, serialize, sizeofHead, Type } from "."
+import { isHeadless, isSerializableType, parse, serialize, sizeof, sizeofHead, Type } from "."
 
 export function ConstArray(size) {
   const obj = { _size: size }
@@ -7,39 +7,82 @@ export function ConstArray(size) {
   return obj
 }
 ConstArray.prototype.serialize = function(dv, src, ...inner_types) {
-  const item_size = sizeofHead(src[0])
+  const item_headless = isHeadless(...inner_types)
+  const item_head_size = sizeofHead(src[0], ...inner_types)
   const size = this._size
 
-  if (dv.byteLength < size * item_size) {
-    throw new Error('too small buffer')
+  if (dv.byteLength < this.sizeof(src, ...inner_types)) {
+    throw new Error(this.name_+ ', ' + inner_types.join(', ') + ' too small buffer')
   }
   if (src.length != size) {
-    throw new Error('array should be ' + size + ' elements length')
+    throw new Error(this.name_+ ', ' + inner_types.join(', ') + ' should be ' + size + ' elements length')
   }
 
+  let offset = item_head_size * size
+
   for (let i = 0; i < size; i++) {
-    const item_frame = new DataView(dv.buffer, dv.byteOffset + item_size * i)
-    serialize(item_frame, src[i], ...inner_types)
+    const item_head_frame = new DataView(dv.buffer, dv.byteOffset + item_head_size * i)
+    if (item_headless) {
+      item_head_frame.setUint32(0, offset)
+      const item_frame = new DataView(dv.buffer, dv.byteOffset + offset)
+      serialize(item_frame, src[i], ...inner_types)
+      offset += sizeof(src[i], ...inner_types)
+    } else {
+      serialize(item_head_frame, src[i], ...inner_types)
+    }
   }
   return
 }
-ConstArray.prototype.parse = function(dv, ...inner_types) { 
+ConstArray.prototype.parse = function(dv, ...inner_types) {
+  const item_headless = isHeadless(...inner_types)
+  const item_head_size = sizeofHead(...inner_types)
   const size = this._size
-  const item_size = sizeofHead(...inner_types)
   const array = Array(size)
 
   for (let i = 0; i < size; i++) {
-    const item_frame = new DataView(dv.buffer, dv.byteOffset + item_size * i)
-    array[i] = parse(item_frame, ...inner_types)
+    const item_head_frame = new DataView(dv.buffer, dv.byteOffset + item_head_size * i)
+    if (item_headless) {
+      const offset = item_head_frame.getUint32(0)
+      const item_frame = new DataView(dv.buffer, dv.byteOffset + offset)
+      array[i] = parse(item_frame, ...inner_types)
+    } else {
+      array[i] = parse(item_head_frame, ...inner_types)
+    }
   }
 
   return array
 }
-ConstArray.prototype.isHeadless = function() {
-  return false
+ConstArray.prototype.isHeadless = function(...inner_types) {
+  return isHeadless(...inner_types)
 }
-ConstArray.prototype.sizeof = function(...inner_types) {
-  return sizeofHead(...inner_types) * this._size
+ConstArray.prototype.sizeof = function(arg, ...args) {
+  let inner_types
+  let src
+
+  if (isSerializableType(arg)) {
+    src = undefined
+    inner_types = [arg, ...args]
+  } else {
+    src = arg
+    inner_types = args
+  }
+
+  const fixed_size = sizeofHead(...inner_types) * this._size
+  
+  if (isHeadless(...inner_types)) {
+    if (src == undefined) {
+      throw new Error('unknown sizeof ' + this._name + ', ' + inner_types.join(','))
+    }
+
+    let variable_size = 0
+    for (const item of src) {
+      variable_size += sizeof(item, ...inner_types)
+    }
+
+    return fixed_size + variable_size
+  } else {
+    return fixed_size
+  }  
 }
 Object.setPrototypeOf(ConstArray.prototype, Type.prototype)
 Object.freeze(ConstArray.prototype)
diff --git a/src/ConstDataView.js b/src/ConstDataView.js
index 430b90e..b8d381e 100644
--- a/src/ConstDataView.js
+++ b/src/ConstDataView.js
@@ -8,10 +8,10 @@ export function ConstDataView(size) {
 }
 ConstDataView.prototype.serialize = function(dv, src) {
   if (dv.byteLength < this._size) {
-    throw new Error('too small buffer')
+    throw new Error(this._name + ' too small buffer')
   }
   if (src.byteLength != this._size) {
-    throw new Error('buffer should be ' + this._size + ' bytes length')
+    throw new Error(this._name + ' should be ' + this._size + ' bytes length')
   }
   memcpy(dv, src)
   return
diff --git a/src/ConstString.js b/src/ConstString.js
index db9e28c..33ae5ce 100644
--- a/src/ConstString.js
+++ b/src/ConstString.js
@@ -12,10 +12,10 @@ ConstString.prototype.serialize = function(dv, src) {
   const encoded = new DataView(encoder.encode(src).buffer, 0, this._size)
 
   if (dv.byteLength < encoded.byteLength) {
-    throw new Error('too small buffer')
+    throw new Error(this._name + ' too small buffer')
   }
   if (src.length != this._size) {
-    throw new Error('string should be ' + this._size + ' symbols length')
+    throw new Error(this._name + ' should be ' + this._size + ' symbols length')
   }
 
   memcpy(dv, encoded)
diff --git a/src/Int.js b/src/Int.js
index 669c4e3..7d2cf47 100644
--- a/src/Int.js
+++ b/src/Int.js
@@ -27,7 +27,7 @@ export function Int(bits, sign) {
       break
 
     default:
-      throw new Error('incorrect bits ' + bits)
+      throw new Error(obj._name + ' incorrect bits ' + bits)
     }
     break
 
@@ -52,25 +52,25 @@ export function Int(bits, sign) {
       break
 
     default:
-      throw new Error('incorrect bits ' + bits)
+      throw new Error(obj._name + ' incorrect bits ' + bits)
     }
     break
 
   default:
-    throw new Error('incorrect sign ' + sign)
+    throw new Error(obj._name + ' incorrect sign ' + sign)
   }
 
   return obj
 }
 Int.prototype.serialize = function (dv, src) {
   if (dv.byteLength < this._size) {
-    throw new Error('buffer is too small')
+    throw new Error(this._name + ' buffer is too small')
   }
   if (src > this._limits.MAX_VALUE) {
-    throw new Error(`number should be less or equal than ` + this._limits.MAX_VALUE)
+    throw new Error(this._name + ` should be less or equal than ` + this._limits.MAX_VALUE)
   }
   if (src < this._limits.MIN_VALUE) {
-    throw new Error(`number should be more or equal than ` + this._limits.MIN_VALUE)
+    throw new Error(this._name + ` should be more or equal than ` + this._limits.MIN_VALUE)
   }
   this._dv_set.call(dv, 0, src)
 }
diff --git a/src/index.js b/src/index.js
index 5198741..b1f76c4 100644
--- a/src/index.js
+++ b/src/index.js
@@ -14,14 +14,14 @@ export function serialize(dv, src, ...types) {
 
   if (type == Boolean && typeof src == 'boolean') {
     if (dv.byteLength < 1) {
-      throw new Error('too small buffer')
+      throw new Error('Boolean too small buffer')
     }
     dv.setUint8(0, src ? 1 : 0)
     return
   }
   if (type == Number && typeof src == 'number') {
     if (dv.byteLength < 8) {
-      throw new Error('too small buffer')
+      throw new Error('Number too small buffer')
     }
     dv.setFloat64(0, src)
     return
@@ -31,10 +31,10 @@ export function serialize(dv, src, ...types) {
     let encoded = new DataView(encoder.encode(src).buffer)
 
     if (dv.byteLength < 4 + encoded.byteLength) {
-      throw new Error('too small buffer')
+      throw new Error('String too small buffer')
     }
     if (encoded.byteLength > limits.u32.MAX_VALUE) {
-      throw new Error('string is too long')
+      throw new Error('String is too long')
     }
 
     dv.setUint32(0, encoded.byteLength)
@@ -44,31 +44,40 @@ export function serialize(dv, src, ...types) {
     return
   }
   if (type == Array && Array.isArray(src)) {
-
-    const item_size = sizeofHead(src[0])
+    const item_headless = isHeadless(...inner_types)
+    const item_head_size = sizeofHead(...inner_types)
     const size = src.length
 
-    if (dv.byteLength < 4 + size * item_size) {
-      throw new Error('too small buffer')
+    if (dv.byteLength < sizeof(src, ...types)) {
+      throw new Error('Array, ' + inner_types.join(', ') + ' too small buffer')
     }
     if (size > limits.u32.MAX_VALUE) {
-      throw new Error('array is too long')
+      throw new Error('Array, ' + inner_types.join(', ') + ' is too long')
     }
 
     dv.setUint32(0, size)
 
+    let offset = 4 + item_head_size * size
+
     for (let i = 0; i < size; i++) {
-      const item_frame = new DataView(dv.buffer, dv.byteOffset + 4 + item_size * i)
-      serialize(item_frame, src[i], ...inner_types)
+      const item_head_frame = new DataView(dv.buffer, dv.byteOffset + 4 + item_head_size * i)
+      if (item_headless) {
+        item_head_frame.setUint32(0, offset)
+        const item_frame = new DataView(dv.buffer, dv.byteOffset + offset)
+        serialize(item_frame, src[i], ...inner_types)
+        offset += sizeof(src[i], ...inner_types)
+      } else {
+        serialize(item_head_frame, src[i], ...inner_types)
+      }
     }
     return
   }
   if (type == DataView && src instanceof DataView) {
     if (dv.byteLength < 4 + src.byteLength) {
-      throw new Error('too small buffer')
+      throw new Error('DataView too small buffer')
     }
     if (src.byteLength > limits.u32.MAX_VALUE) {
-      throw new Error('data view is too long')
+      throw new Error('DataView data is too long')
     }
 
     dv.setUint32(0, src.byteLength)
@@ -99,13 +108,20 @@ export function parse(dv, ...types) {
     return decoder.decode(frame)
   }
   if (type == Array) {
+    const item_headless = isHeadless(...inner_types)
+    const item_head_size = sizeofHead(...inner_types)
     const size = dv.getUint32(0)
-    const item_size = sizeofHead(inner_types[0])
     const array = Array(size)
 
     for (let i = 0; i < size; i++) {
-      const item_frame = new DataView(dv.buffer, dv.byteOffset + 4 + item_size * i)
-      array[i] = parse(item_frame, ...inner_types)
+      const item_head_frame = new DataView(dv.buffer, dv.byteOffset + 4 + item_head_size * i)
+      if (item_headless) {
+        const offset = item_head_frame.getUint32(0)
+        const item_frame = new DataView(dv.buffer, dv.byteOffset + offset)
+        array[i] = parse(item_frame, ...inner_types)
+      } else {
+        array[i] = parse(item_head_frame, ...inner_types)
+      }
     }
 
     return array
@@ -148,29 +164,50 @@ export function sizeofHead(...args) {
 
 export function sizeof(...args) {
   const [arg, ...inner_args] = args
+  const [arg2, ...inner_args2] = inner_args
 
-  if (arg == Boolean || typeof arg == 'boolean') {
+  if (arg == Boolean || arg2 == Boolean && typeof arg == 'boolean') {
     return 1
   }
-  if (arg == Number || typeof arg == 'number') {
+  if (arg == Number || arg2 == Number && typeof arg == 'number') {
     return 8
   }
-  if (typeof arg == 'string') {
+  if (arg2 == String && typeof arg == 'string') {
     const encoder = new TextEncoder('utf-8')
     return 4 + encoder.encode(arg).byteLength
   }
-  if (Array.isArray(arg)) {
-    return 4 + sizeofHead(arg[0]) * arg.length
+  if (arg2 == Array && Array.isArray(arg)) {
+    
+    const fixed_size = 4 + sizeofHead(...inner_args2) * arg.length
+    if (isHeadless(...inner_args2)) {
+
+      let variable_size = 0
+      for (const item of arg) {
+        variable_size += sizeof(item, ...inner_args2)
+      }
+
+      return fixed_size + variable_size
+    } else {
+      return fixed_size
+    }
   }
-  if (arg instanceof DataView) {
+  if (arg2 == DataView && arg instanceof DataView) {
     return 4 + arg.byteLength
   }
   if (arg instanceof Type) {
     return arg.sizeof(...inner_args)
   }
-  const [arg2, ...inner_args2] = inner_args
   if (arg2 instanceof Type) {
     return arg2.sizeof(arg, ...inner_args2)
   }
-  throw new Error('unknown size of ' + arg)
+  throw new Error('unknown size of ' + args)
+}
+
+export function isSerializableType(type) {
+  return type == Boolean ||
+    type == Number ||
+    type == String ||
+    type == Array ||
+    type == DataView ||
+    type instanceof Type
 }
diff --git a/test/ConstArray.test.js b/test/ConstArray.test.js
index 5e6459f..43e61a9 100644
--- a/test/ConstArray.test.js
+++ b/test/ConstArray.test.js
@@ -1,5 +1,5 @@
 import { describe, expect, test } from "vitest";
-import { ConstArray, parse, serialize, sizeof, sizeofHead } from "../src";
+import { ConstArray, isHeadless, parse, serialize, sizeof, sizeofHead } from "../src";
 import { expectDataViewEqual, filledDataView, sizedDataView } from ".";
 
 describe(ConstArray.name, () => {
@@ -33,4 +33,41 @@ describe(ConstArray.name, () => {
   test('sizeof', () => {
     expect(sizeofHead(ConstArray(2), Number)).toEqual(16)
   })
+
+  const array_dv = filledDataView([
+    0x00, 0x00, 0x00, 0x08,
+    0x00, 0x00, 0x00, 0x11,
+    // hello
+    0x00, 0x00, 0x00, 0x05,
+    0x68, 0x65, 0x6C, 0x6C, 0x6F,
+    // sek1ro
+    0x00, 0x00, 0x00, 0x06,
+    0x73, 0x65, 0x6b, 0x31, 0x72, 0x6f,
+  ])
+  const array = ['hello', 'sek1ro']
+
+  test('serialize, String', () => {
+
+    const actual = sizedDataView(sizeof(array, ConstArray(2), String))
+    
+    expect(() => sizeof(ConstArray(2), String)).toThrow()
+
+    serialize(actual, array, ConstArray(2), String)
+    expectDataViewEqual(actual, array_dv)
+  })
+
+  test('parse, String', () => {
+    expect(parse(array_dv, ConstArray(2), String)).toEqual(array)
+  })
+
+  test('isHeadless', () => {
+    expect(isHeadless(ConstArray(2), Number)).toBeFalsy()
+    expect(isHeadless(ConstArray(2), String)).toBeTruthy()
+  })
+
+  test('sizeof', () => {
+    expect(sizeof(ConstArray(2), Number)).toBe(16)
+    expect(() => sizeof(ConstArray(2), String)).toThrow()
+    expect(sizeof(['hello', 'sek1ro'], ConstArray(2), String)).toBe(27)
+  })
 })
diff --git a/test/index.test.js b/test/index.test.js
index 2fe8c86..c5de580 100644
--- a/test/index.test.js
+++ b/test/index.test.js
@@ -1,6 +1,6 @@
 import { describe, test, expect } from 'vitest'
 import { expectDataViewEqual, filledDataView, sizedDataView } from '.'
-import { parse, serialize, sizeof, sizeofHead } from '../src'
+import { isHeadless, parse, serialize, sizeof, sizeofHead } from '../src'
 
 describe('serialize', () => {
   test('Boolean', () => {
@@ -32,7 +32,7 @@ describe('serialize', () => {
     let dv = sizedDataView(8)
     expect(() => serialize(dv, 'hello', String)).toThrow()
 
-    dv = sizedDataView(sizeof('hello'))
+    dv = sizedDataView(sizeof('hello', String))
     expect(9).toEqual(dv.byteLength)
 
     serialize(dv, 'hello', String)
@@ -47,12 +47,30 @@ describe('serialize', () => {
     let dv = sizedDataView(19)
     expect(() => serialize(dv, [1, 2], Array, Number)).toThrow()
     
-    dv = sizedDataView(sizeof([1, 2]))
+    dv = sizedDataView(sizeof([1, 2], Array, Number))
     expect(20).toEqual(dv.byteLength)
 
     serialize(dv, [1, 2], Array, Number)
     expectDataViewEqual(dv, expected)
   })
+  test('Array, String', () => {
+    const expected = filledDataView([
+      0x00, 0x00, 0x00, 0x02,
+      0x00, 0x00, 0x00, 0x0C,
+      0x00, 0x00, 0x00, 0x15,
+      // hello
+      0x00, 0x00, 0x00, 0x05,
+      0x68, 0x65, 0x6C, 0x6C, 0x6F,
+      // sek1ro
+      0x00, 0x00, 0x00, 0x06,
+      0x73, 0x65, 0x6b, 0x31, 0x72, 0x6f,
+    ])
+    const array = ['hello', 'sek1ro']
+    const actual = sizedDataView(sizeof(array, Array, String))
+
+    serialize(actual, array, Array, String)
+    expectDataViewEqual(actual, expected)
+  })
   test('DataView', () => {
     const expected = filledDataView([
       0x00, 0x00, 0x00, 0x04,
@@ -100,6 +118,22 @@ describe('parse', () => {
     const actual = parse(dv, Array, Number)
     expect(actual).toEqual(expected)
   })
+  test('Array, String', () => {
+    const expected = ['hello', 'sek1ro']
+    const dv = filledDataView([
+      0x00, 0x00, 0x00, 0x02,
+      0x00, 0x00, 0x00, 0x0C,
+      0x00, 0x00, 0x00, 0x15,
+      // hello
+      0x00, 0x00, 0x00, 0x05,
+      0x68, 0x65, 0x6C, 0x6C, 0x6F,
+      // sek1ro
+      0x00, 0x00, 0x00, 0x06,
+      0x73, 0x65, 0x6b, 0x31, 0x72, 0x6f,
+    ])
+    const actual = parse(dv, Array, String)
+    expect(actual).toEqual(expected)
+  })
   test('DataView', () => {
     const expected = filledDataView([
       0x00, 0x01, 0x02, 0x03,
@@ -113,22 +147,28 @@ describe('parse', () => {
   })
 })
 
+describe('isHeadless', () => {
+  test('Array', () => {
+    expect(isHeadless(Array, Number)).toBeTruthy()
+    expect(isHeadless(Array, String)).toBeTruthy()
+  })
+})
+
 describe('sizeofHead', () => {
+  test('Boolean', () => {
+    expect(sizeofHead(Boolean)).toEqual(1)
+  })
   test('Number', () => {
     expect(sizeofHead(Number)).toEqual(8)
-    expect(sizeofHead(1, Number)).toEqual(8)
   })
   test('String', () => {
     expect(sizeofHead(String)).toEqual(4)
-    expect(sizeofHead('s', String)).toEqual(4)
   })
   test('Array', () => {
     expect(sizeofHead(Array, Number)).toEqual(4)
-    expect(sizeofHead([1], Array, Number)).toEqual(4)
   })
   test('DataView', () => {
     expect(sizeofHead(DataView)).toEqual(4)
-    expect(sizeofHead(filledDataView([0x01]), DataView)).toEqual(4)
   })
 })
 
diff --git a/types/index.d.ts b/types/index.d.ts
index 30106e9..df65d0a 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -28,14 +28,6 @@ export function serialize(dv: DataView, src: Serializable, ...types: Serializabl
   */
 export function parse(dv: DataView, ...types: SerializableType[]): Serializable;
 
-/**
-  * some types, like Array, String, has no fixed size. So in Structure they are stored as u32 offset, which points to their beginning
-  * @param {Serializable} obj to check
-  * @param {SerializableType[]} ...types primary and inner types. eg: Array, Number
-  * @returns {boolean}
-  */
-export function isHeadless(obj: Serializable, ...types: SerializableType[]): boolean;
-
 /**
   * some types, like Array, String, has no fixed size. So in Structure they are stored as u32 offset, which points to their beginning
   * @param {SerializableType[]} ...types primary and inner types. eg: Array, Number
@@ -43,14 +35,6 @@ export function isHeadless(obj: Serializable, ...types: SerializableType[]): boo
   */
 export function isHeadless(...types: SerializableType[]): boolean;
 
-/**
-  * if obj has no fixed size, return 4 (sizeof u32 offset)
-  * @param {Serializable} obj to check
-  * @param {SerializableType[]} ...types primary and inner types. eg: Array, Number
-  * @returns {number}
-  */
-export function sizeofHead(obj: Serializable, ...types: SerializableType[]): number;
-
 /**
   * if obj has no fixed size, return 4 (sizeof u32 offset)
   * @param {SerializableType[]} ...types primary and inner types. eg: Array, Number
@@ -71,3 +55,5 @@ export function sizeof(obj: Serializable, ...types: SerializableType[]): number;
   * @throws {Error} if passed Array, String, DataView type (unknown sizeof)
   */
 export function sizeof(...types: SerializableType[]): number;
+
+export function isSerializableType(type: unknown): boolean;