diff --git a/assert/assert.d.ts b/assert/assert.d.ts
index bccf4fef9..e334b87e9 100644
--- a/assert/assert.d.ts
+++ b/assert/assert.d.ts
@@ -57,6 +57,7 @@ declare module assert {
 //     export = assert;
 // }
 
+// move to power-assert.d.ts. do not use this definition file.
 declare module "power-assert" {
     export = assert;
 }
diff --git a/empower/empower-tests.ts b/empower/empower-tests.ts
new file mode 100644
index 000000000..27b1894c6
--- /dev/null
+++ b/empower/empower-tests.ts
@@ -0,0 +1,17 @@
+/// <reference path="./empower.d.ts" />
+
+var baseAssert:any;
+var fakeFormatter:any;
+
+()=> {
+    var assert = empower(baseAssert, fakeFormatter);
+};
+
+var option:empower.Options = {
+    modifyMessageOnRethrow: false,
+    saveContextOnRethrow: false
+};
+
+()=> {
+    var assert = empower(baseAssert, fakeFormatter, option);
+};
diff --git a/empower/empower.d.ts b/empower/empower.d.ts
new file mode 100644
index 000000000..bf4f3d687
--- /dev/null
+++ b/empower/empower.d.ts
@@ -0,0 +1,19 @@
+// Type definitions for empower
+// Project: https://github.com/twada/empower
+// Definitions by: vvakame <https://github.com/vvakame>
+// Definitions: https://github.com/borisyankov/DefinitelyTyped
+
+declare function empower(originalAssert:any, formatter:any, options?:empower.Options):any;
+
+declare module empower {
+    export interface Options {
+        destructive?: boolean;
+        modifyMessageOnRethrow?: boolean;
+        saveContextOnRethrow?: boolean;
+        patterns?: string[];
+    }
+}
+
+declare module "empower" {
+    export = empower;
+}
diff --git a/power-assert-formatter/power-assert-formatter-tests.ts b/power-assert-formatter/power-assert-formatter-tests.ts
new file mode 100644
index 000000000..cd5a2680d
--- /dev/null
+++ b/power-assert-formatter/power-assert-formatter-tests.ts
@@ -0,0 +1,5 @@
+/// <reference path="./power-assert-formatter.d.ts" />
+
+powerAssertFormatter();
+
+powerAssertFormatter({lineSeparator: '\n'});
diff --git a/power-assert-formatter/power-assert-formatter.d.ts b/power-assert-formatter/power-assert-formatter.d.ts
new file mode 100644
index 000000000..d3ccb59ab
--- /dev/null
+++ b/power-assert-formatter/power-assert-formatter.d.ts
@@ -0,0 +1,29 @@
+// Type definitions for power-assert-formatter
+// Project: https://github.com/twada/power-assert-formatter
+// Definitions by: vvakame <https://github.com/vvakame>
+// Definitions: https://github.com/borisyankov/DefinitelyTyped
+
+declare function powerAssertFormatter(options?:powerAssertFormatter.Options):powerAssertFormatter.Formatter;
+
+declare module powerAssertFormatter {
+    export interface Options {
+        lineDiffThreshold?: number;
+        maxDepth?: number;
+        outputOffset?: number;
+        anonymous?: string;
+        circular?: string;
+        lineSeparator?: string;
+        ambiguousEastAsianCharWidth?: number;
+        widthOf?: Function;
+        stringify?: Function;
+        diff?: Function;
+        writerClass?: {new (): any;};
+        renderers?: any[]; // { string | Function }[]
+    }
+
+    export interface Formatter {
+        (powerAssertContext:any): string;
+    }
+
+    export function defaultOptions():Options;
+}
diff --git a/power-assert/power-assert-tests.ts b/power-assert/power-assert-tests.ts
new file mode 100644
index 000000000..f7be7059f
--- /dev/null
+++ b/power-assert/power-assert-tests.ts
@@ -0,0 +1,83 @@
+/// <reference path="./power-assert.d.ts" />
+
+import assert = require("power-assert");
+
+assert(1 + 1 - 2 === 0, "The universe isn't how it should.");
+
+assert.deepEqual({x: {y: 3}}, {x: {y: 3}}, "DEEP WENT DERP");
+
+assert.equal(3, "3", "uses == comparator");
+
+assert.notStrictEqual(2, "2", "uses === comparator");
+
+assert.throws(() => {
+    throw "a hammer at your face";
+}, undefined, "DODGED IT");
+
+assert.doesNotThrow(() => {
+    if (false) {
+        throw "a hammer at your face";
+    }
+}, undefined, "What the...*crunch*");
+
+
+var customizedAssert1 = assert.customize({
+    output: {
+        maxDepth: 2
+    }
+});
+
+customizedAssert1(1 + 1 - 2 === 0, "The universe isn't how it should.");
+
+customizedAssert1.deepEqual({x: {y: 3}}, {x: {y: 3}}, "DEEP WENT DERP");
+
+customizedAssert1.equal(3, "3", "uses == comparator");
+
+customizedAssert1.notStrictEqual(2, "2", "uses === comparator");
+
+customizedAssert1.throws(() => {
+    throw "a hammer at your face";
+}, undefined, "DODGED IT");
+
+customizedAssert1.doesNotThrow(() => {
+    if (false) {
+        throw "a hammer at your face";
+    }
+}, undefined, "What the...*crunch*");
+
+
+var customizedAssert2 = assert.customize({
+    assertion: {
+        destructive: false,
+        modifyMessageOnRethrow: true,
+        saveContextOnRethrow: true,
+        patterns: [
+            'assert(value, [message])',
+            'assert.ok(value, [message])',
+            'assert.equal(actual, expected, [message])',
+            'assert.notEqual(actual, expected, [message])',
+            'assert.strictEqual(actual, expected, [message])',
+            'assert.notStrictEqual(actual, expected, [message])',
+            'assert.deepEqual(actual, expected, [message])',
+            'assert.notDeepEqual(actual, expected, [message])'
+        ]
+    },
+    output: {
+        lineDiffThreshold: 5,
+        maxDepth: 1,
+        anonymous: 'Object',
+        circular: '#@Circular#',
+        lineSeparator: '\n',
+        ambiguousEastAsianCharWidth: 2,
+        widthOf: () => null,
+        stringify: () => null,
+        diff: () => null,
+        writerClass: null,
+        renderers: [
+            './built-in/file',
+            './built-in/assertion',
+            './built-in/diagram',
+            './built-in/binary-expression'
+        ]
+    }
+});
diff --git a/power-assert/power-assert.d.ts b/power-assert/power-assert.d.ts
new file mode 100644
index 000000000..203edc052
--- /dev/null
+++ b/power-assert/power-assert.d.ts
@@ -0,0 +1,66 @@
+// Type definitions for power-assert
+// Project: https://github.com/twada/power-assert
+// Definitions by: vvakame <https://github.com/vvakame>
+// Definitions: https://github.com/borisyankov/DefinitelyTyped
+
+// copy from assert external module in node.d.ts
+
+/// <reference path="../empower/empower.d.ts" />
+/// <reference path="../power-assert-formatter/power-assert-formatter.d.ts" />
+
+declare function assert(value:any, message?:string):void;
+declare module assert {
+    export class AssertionError implements Error {
+        name:string;
+        message:string;
+        actual:any;
+        expected:any;
+        operator:string;
+        generatedMessage:boolean;
+
+        constructor(options?:{message?: string; actual?: any; expected?: any; operator?: string; stackStartFunction?: Function});
+    }
+
+    export function fail(actual?:any, expected?:any, message?:string, operator?:string):void;
+
+    export function ok(value:any, message?:string):void;
+
+    export function equal(actual:any, expected:any, message?:string):void;
+
+    export function notEqual(actual:any, expected:any, message?:string):void;
+
+    export function deepEqual(actual:any, expected:any, message?:string):void;
+
+    export function notDeepEqual(acutal:any, expected:any, message?:string):void;
+
+    export function strictEqual(actual:any, expected:any, message?:string):void;
+
+    export function notStrictEqual(actual:any, expected:any, message?:string):void;
+
+    export var throws:{
+        (block:Function, message?:string): void;
+        (block:Function, error:Function, message?:string): void;
+        (block:Function, error:RegExp, message?:string): void;
+        (block:Function, error:(err:any) => boolean, message?:string): void;
+    };
+
+    export var doesNotThrow:{
+        (block:Function, message?:string): void;
+        (block:Function, error:Function, message?:string): void;
+        (block:Function, error:RegExp, message?:string): void;
+        (block:Function, error:(err:any) => boolean, message?:string): void;
+    };
+
+    export function ifError(value:any):void;
+
+    export interface Options {
+        assertion?: empower.Options;
+        output?: powerAssertFormatter.Options;
+    }
+
+    export function customize(options:Options):typeof assert;
+}
+
+declare module "power-assert" {
+    export = assert;
+}