diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..153d416
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,165 @@
+                   GNU LESSER GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+
+  This version of the GNU Lesser General Public License incorporates
+the terms and conditions of version 3 of the GNU General Public
+License, supplemented by the additional permissions listed below.
+
+  0. Additional Definitions.
+
+  As used herein, "this License" refers to version 3 of the GNU Lesser
+General Public License, and the "GNU GPL" refers to version 3 of the GNU
+General Public License.
+
+  "The Library" refers to a covered work governed by this License,
+other than an Application or a Combined Work as defined below.
+
+  An "Application" is any work that makes use of an interface provided
+by the Library, but which is not otherwise based on the Library.
+Defining a subclass of a class defined by the Library is deemed a mode
+of using an interface provided by the Library.
+
+  A "Combined Work" is a work produced by combining or linking an
+Application with the Library.  The particular version of the Library
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+Version".
+
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+Corresponding Source for the Combined Work, excluding any source code
+for portions of the Combined Work that, considered in isolation, are
+based on the Application, and not on the Linked Version.
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+object code and/or source code for the Application, including any data
+and utility programs needed for reproducing the Combined Work from the
+Application, but excluding the System Libraries of the Combined Work.
+
+  1. Exception to Section 3 of the GNU GPL.
+
+  You may convey a covered work under sections 3 and 4 of this License
+without being bound by section 3 of the GNU GPL.
+
+  2. Conveying Modified Versions.
+
+  If you modify a copy of the Library, and, in your modifications, a
+facility refers to a function or data to be supplied by an Application
+that uses the facility (other than as an argument passed when the
+facility is invoked), then you may convey a copy of the modified
+version:
+
+   a) under this License, provided that you make a good faith effort to
+   ensure that, in the event an Application does not supply the
+   function or data, the facility still operates, and performs
+   whatever part of its purpose remains meaningful, or
+
+   b) under the GNU GPL, with none of the additional permissions of
+   this License applicable to that copy.
+
+  3. Object Code Incorporating Material from Library Header Files.
+
+  The object code form of an Application may incorporate material from
+a header file that is part of the Library.  You may convey such object
+code under terms of your choice, provided that, if the incorporated
+material is not limited to numerical parameters, data structure
+layouts and accessors, or small macros, inline functions and templates
+(ten or fewer lines in length), you do both of the following:
+
+   a) Give prominent notice with each copy of the object code that the
+   Library is used in it and that the Library and its use are
+   covered by this License.
+
+   b) Accompany the object code with a copy of the GNU GPL and this license
+   document.
+
+  4. Combined Works.
+
+  You may convey a Combined Work under terms of your choice that,
+taken together, effectively do not restrict modification of the
+portions of the Library contained in the Combined Work and reverse
+engineering for debugging such modifications, if you also do each of
+the following:
+
+   a) Give prominent notice with each copy of the Combined Work that
+   the Library is used in it and that the Library and its use are
+   covered by this License.
+
+   b) Accompany the Combined Work with a copy of the GNU GPL and this license
+   document.
+
+   c) For a Combined Work that displays copyright notices during
+   execution, include the copyright notice for the Library among
+   these notices, as well as a reference directing the user to the
+   copies of the GNU GPL and this license document.
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+   d) Do one of the following:
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+       the Linked Version to produce a modified Combined Work, in the
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+       Corresponding Source.
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+       Library.  A suitable mechanism is one that (a) uses at run time
+       a copy of the Library already present on the user's computer
+       system, and (b) will operate properly with a modified version
+       of the Library that is interface-compatible with the Linked
+       Version.
+
+   e) Provide Installation Information, but only if you would otherwise
+   be required to provide such information under section 6 of the
+   GNU GPL, and only to the extent that such information is
+   necessary to install and execute a modified version of the
+   Combined Work produced by recombining or relinking the
+   Application with a modified version of the Linked Version. (If
+   you use option 4d0, the Installation Information must accompany
+   the Minimal Corresponding Source and Corresponding Application
+   Code. If you use option 4d1, you must provide the Installation
+   Information in the manner specified by section 6 of the GNU GPL
+   for conveying Corresponding Source.)
+
+  5. Combined Libraries.
+
+  You may place library facilities that are a work based on the
+Library side by side in a single library together with other library
+facilities that are not Applications and are not covered by this
+License, and convey such a combined library under terms of your
+choice, if you do both of the following:
+
+   a) Accompany the combined library with a copy of the same work based
+   on the Library, uncombined with any other library facilities,
+   conveyed under the terms of this License.
+
+   b) Give prominent notice with the combined library that part of it
+   is a work based on the Library, and explaining where to find the
+   accompanying uncombined form of the same work.
+
+  6. Revised Versions of the GNU Lesser General Public License.
+
+  The Free Software Foundation may publish revised and/or new versions
+of the GNU Lesser General Public License from time to time. Such new
+versions will be similar in spirit to the present version, but may
+differ in detail to address new problems or concerns.
+
+  Each version is given a distinguishing version number. If the
+Library as you received it specifies that a certain numbered version
+of the GNU Lesser General Public License "or any later version"
+applies to it, you have the option of following the terms and
+conditions either of that published version or of any later version
+published by the Free Software Foundation. If the Library as you
+received it does not specify a version number of the GNU Lesser
+General Public License, you may choose any version of the GNU Lesser
+General Public License ever published by the Free Software Foundation.
+
+  If the Library as you received it specifies that a proxy can decide
+whether future versions of the GNU Lesser General Public License shall
+apply, that proxy's public statement of acceptance of any version is
+permanent authorization for you to choose that version for the
+Library.
\ No newline at end of file
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..f3774c1
--- /dev/null
+++ b/README.md
@@ -0,0 +1,68 @@
+# serialize-js
+
+```js
+import * as s from '@sek1ro/serialize'
+
+const User = s.Struct({
+  id: s.Int(32, 'unsigned'),
+  name: String,
+  age: Number,
+  array: [Array, Boolean],
+  raw_data: DataView,
+})
+
+const user = {
+  id: 1,
+  name: 'john',
+  age: 20,
+  array: [true, false],
+  raw_data: s.filledDataView([0x00, 0x00, 0x00, 0xff]),
+}
+
+const dv = s.sizedDataView(sizeof(user, User))
+s.serialize(dv, user, User)
+
+const user_copy = s.parse(dv, User)
+```
+
+## Contents
+
+- [Types](#types)
+- [What is headless?](#headless)
+
+## Types
+
+### ES types
+
+- Boolean
+- Number
+- String (headless)
+- Array (headless)
+- DataView (headless)
+
+### Built-in types
+
+- Int(bits: 8 | 16 | 32, sign: 'signed' | 'unsigned')
+- ConstString(size: number)
+- ConstArray(size: number)
+- ConstDataView(byte_size: number)
+- Struct(type_obj: Record<string, SerializableType | SerializableType[]>)
+- Sequence(types: (SerializableType | SerializableType[])[])
+
+## Headless
+
+If type has variable size in bytes, if sizeof type different for specific object, it's called headless.
+
+```js
+const array = [true, false]
+
+sizeof(ConstArray(2), Boolean) // 2
+sizeof(array, ConstArray(2), Boolean) // 2
+
+sizeof(Array, Boolean) // Error: unknown sizeof Array, Boolean
+
+sizeof(array, Array, Boolean) // 2
+```
+
+Library has function `isHeadless(...types: SerializableType[])` to check this.
+It's used in `Structure`, if type is headless, in head of structure it's stored as uint32 offset to beginning of type's body, if type isn't headless, it's stored directly in head of structure
diff --git a/package.json b/package.json
index 7d4c8e1..06bf669 100644
--- a/package.json
+++ b/package.json
@@ -11,7 +11,9 @@
   "type": "module",
   "main": "dist/index.js",
   "files": [
-    "dist"
+    "dist",
+    "LICENSE",
+    "README.md"
   ],
   "scripts": {
     "build": "npx esbuild src/index.js --bundle --minify --outfile=dist/index.js --format=esm && npx rollup -c",
diff --git a/src/Struct.js b/src/Struct.js
index fc27a6c..1a89d03 100644
--- a/src/Struct.js
+++ b/src/Struct.js
@@ -18,7 +18,13 @@ export function Struct(type_obj) {
       types = [value]
     }
 
-    arg[key] = types.map((type) => type.name)
+    arg[key] = types.map((type) => {
+      if (typeof type == 'function') {
+        return type.name
+      } else {
+        return type
+      }
+    })
 
     const headless = isHeadless(...types)
     obj._info_by_key.set(key, {
diff --git a/src/index.js b/src/index.js
index 3fd4eb1..e89a553 100644
--- a/src/index.js
+++ b/src/index.js
@@ -1,5 +1,5 @@
 import { limits } from './limits'
-import { memcpy } from './mem'
+import { sizedDataView, filledDataView, memcpy } from './mem'
 import { Type } from './Type'
 import { Int } from './Int'
 import { ConstString } from './ConstString'
@@ -10,6 +10,8 @@ import { Struct } from './Struct'
 
 export {
   limits,
+  sizedDataView,
+  filledDataView,
   memcpy,
   Type,
   Int,
@@ -217,7 +219,13 @@ export function sizeof(...args) {
   if (arg2 instanceof Type) {
     return arg2.sizeof(arg, ...inner_args2)
   }
-  throw new Error('unknown size of ' + args)
+  throw new Error(
+    'unknown size of ' +
+      args.map((arg) => {
+        if (typeof arg == 'function') return arg.name
+        return arg
+      }),
+  )
 }
 
 export function isSerializableType(type) {
diff --git a/src/mem.js b/src/mem.js
index baea2bf..76eb4cf 100644
--- a/src/mem.js
+++ b/src/mem.js
@@ -1,3 +1,19 @@
+export function filledDataView(bytes) {
+  const ab = new ArrayBuffer(bytes.length)
+  const dv = new DataView(ab)
+
+  for (let i = 0; i < bytes.length; i++) {
+    dv.setInt8(i, bytes[i])
+  }
+
+  return dv
+}
+
+export function sizedDataView(length) {
+  const ab = new ArrayBuffer(length)
+  return new DataView(ab)
+}
+
 export function memcpy(dest, src) {
   const min_size =
     dest.byteLength > src.byteLength ? src.byteLength : dest.byteLength
diff --git a/test/ConstArray.test.js b/test/ConstArray.test.js
index 43e61a9..856eed7 100644
--- a/test/ConstArray.test.js
+++ b/test/ConstArray.test.js
@@ -1,6 +1,7 @@
 import { describe, expect, test } from "vitest";
 import { ConstArray, isHeadless, parse, serialize, sizeof, sizeofHead } from "../src";
-import { expectDataViewEqual, filledDataView, sizedDataView } from ".";
+import { expectDataViewEqual } from ".";
+import { filledDataView, sizedDataView } from "../src";
 
 describe(ConstArray.name, () => {
   test('serialize, Number', () => {
diff --git a/test/ConstDataView.test.js b/test/ConstDataView.test.js
index cec4e50..c29050b 100644
--- a/test/ConstDataView.test.js
+++ b/test/ConstDataView.test.js
@@ -1,6 +1,7 @@
 import { describe, expect, test } from "vitest";
 import { ConstDataView, parse, serialize, sizeofHead } from "../src";
-import { expectDataViewEqual, filledDataView } from ".";
+import { expectDataViewEqual } from ".";
+import { filledDataView } from "../src";
 
 describe(ConstDataView.name, () => {
   test('serialize', () => {
diff --git a/test/ConstString.test.js b/test/ConstString.test.js
index 9ca5443..7b264d1 100644
--- a/test/ConstString.test.js
+++ b/test/ConstString.test.js
@@ -1,6 +1,7 @@
 import { describe, expect, test } from "vitest";
 import { ConstString, parse, serialize, sizeofHead } from "../src";
-import { expectDataViewEqual, filledDataView, sizedDataView } from ".";
+import { expectDataViewEqual } from ".";
+import { filledDataView, sizedDataView } from '../src'
 
 describe(ConstString.name, () => {
   test('serialize', () => {
diff --git a/test/Int.test.js b/test/Int.test.js
index 50c348c..c31d3ac 100644
--- a/test/Int.test.js
+++ b/test/Int.test.js
@@ -1,5 +1,6 @@
 import { describe, expect, test } from "vitest";
-import { expectDataViewEqual, filledDataView, sizedDataView } from '.';
+import { expectDataViewEqual } from '.';
+import { filledDataView, sizedDataView } from '../src'
 import { Int, parse, serialize, sizeof } from "../src";
 
 describe(Int.name, () => {
diff --git a/test/Sequence.test.js b/test/Sequence.test.js
index 4213455..da1bd71 100644
--- a/test/Sequence.test.js
+++ b/test/Sequence.test.js
@@ -1,6 +1,7 @@
 import { describe, expect, test } from "vitest";
 import { ConstString, Int, isHeadless, parse, Sequence, serialize, sizeof } from "../src";
-import { expectDataViewEqual, filledDataView, sizedDataView } from '.'
+import { expectDataViewEqual } from '.'
+import { filledDataView, sizedDataView } from '../src'
 
 describe(Sequence.name, () => {
   const Type = Sequence([Int(8, 'unsigned'), String, Boolean])
diff --git a/test/Struct.test.js b/test/Struct.test.js
index e17f8a2..d93973a 100644
--- a/test/Struct.test.js
+++ b/test/Struct.test.js
@@ -1,6 +1,7 @@
 import { describe, expect, test } from "vitest";
 import { ConstDataView, parse, serialize, sizeof, Struct } from "../src";
-import { expectDataViewEqual, filledDataView, sizedDataView } from ".";
+import { filledDataView, sizedDataView } from '../src'
+import { expectDataViewEqual } from ".";
 
 describe(Struct.name, () => {
   
diff --git a/test/index.js b/test/index.js
index 63067e9..bf3577c 100644
--- a/test/index.js
+++ b/test/index.js
@@ -1,19 +1,3 @@
-export function filledDataView(bytes) {
-  const ab = new ArrayBuffer(bytes.length)
-  const dv = new DataView(ab)
-
-  for (let i = 0; i < bytes.length; i++) {
-    dv.setInt8(i, bytes[i])
-  }
-
-  return dv
-}
-
-export function sizedDataView(length) {
-  const ab = new ArrayBuffer(length)
-  return new DataView(ab)
-}
-
 export function expectDataViewEqual(actual, expected) {
   const actualBytes = new Uint8Array(actual.buffer, actual.byteOffset, actual.byteLength)
   const expectedBytes = new Uint8Array(expected.buffer, expected.byteOffset, expected.byteLength)
diff --git a/test/index.test.js b/test/index.test.js
index c5de580..4c90530 100644
--- a/test/index.test.js
+++ b/test/index.test.js
@@ -1,6 +1,38 @@
 import { describe, test, expect } from 'vitest'
-import { expectDataViewEqual, filledDataView, sizedDataView } from '.'
-import { isHeadless, parse, serialize, sizeof, sizeofHead } from '../src'
+import { expectDataViewEqual } from '.'
+import { filledDataView, sizedDataView } from '../src'
+import { Int, isHeadless, parse, serialize, sizeof, sizeofHead, Struct } from '../src'
+
+describe('README', () => {
+  test('header', () => {
+    const User = Struct({
+        id: Int(32, 'unsigned'),
+        name: String,
+        age: Number,
+        array: [Array, Boolean],
+        raw_data: DataView,  
+    })
+
+    const user = {
+        id: 1,
+        name: 'john',
+        age: 20,
+        array: [true, false],
+        raw_data: filledDataView([0x00, 0x00, 0x00, 0xFF]),
+    }
+
+    const dv = sizedDataView(sizeof(user, User))
+    serialize(dv, user, User)
+
+    const user_copy = parse(dv, User)
+
+    expect(user_copy).toEqual(user)
+    expectDataViewEqual(user_copy.raw_data, user.raw_data)
+  })
+  test('unknown sizeof', () => {
+    expect(() => sizeof(Array, Boolean)).toThrowError('unknown size of Array,Boolean')
+  })
+})
 
 describe('serialize', () => {
   test('Boolean', () => {
diff --git a/test/mem.test.js b/test/mem.test.js
index bf5a175..480a943 100644
--- a/test/mem.test.js
+++ b/test/mem.test.js
@@ -1,5 +1,5 @@
 import { expect, test } from "vitest";
-import { filledDataView, sizedDataView } from ".";
+import { filledDataView, sizedDataView } from '../src'
 import { memcpy } from "../src";
 
 test('memcpy', () => {
diff --git a/types/index.d.ts b/types/index.d.ts
index da7770e..5c6fdec 100644
--- a/types/index.d.ts
+++ b/types/index.d.ts
@@ -1,4 +1,4 @@
-import { memcpy } from './mem'
+import { sizedDataView, filledDataView, memcpy } from './mem'
 import { limits } from './limits'
 import { Type } from './Type'
 import { Int } from './Int'
@@ -9,6 +9,8 @@ import { Sequence } from './Sequence'
 import { Struct } from './Struct'
 
 export {
+  sizedDataView,
+  filledDataView,
   memcpy,
   limits,
   Type,
diff --git a/types/mem.d.ts b/types/mem.d.ts
index d1b5eb5..1d8495e 100644
--- a/types/mem.d.ts
+++ b/types/mem.d.ts
@@ -1,3 +1,6 @@
+export function sizedDataView(size: number): DataView
+export function filledDataView(bytes: number[]): DataView
+
 /**
  * copies max possible number of bytes from src to dest (min of both sizes)
  */