diff --git a/src/content/InputDriver.ts b/src/content/InputDriver.ts
index 0472088..e77d857 100644
--- a/src/content/InputDriver.ts
+++ b/src/content/InputDriver.ts
@@ -1,5 +1,5 @@
 import * as dom from '../shared/utils/dom';
-import Key, * as keys from './domains/Key';
+import Key from './domains/Key';
 
 const cancelKey = (e: KeyboardEvent): boolean => {
   if (e.key === 'Escape') {
@@ -66,7 +66,7 @@ export default class InputDriver {
       return;
     }
 
-    let key = keys.fromKeyboardEvent(e);
+    let key = Key.fromKeyboardEvent(e);
     for (let listener of this.onKeyListeners) {
       let stop = listener(key);
       if (stop) {
diff --git a/src/content/client/FollowMasterClient.ts b/src/content/client/FollowMasterClient.ts
index da75308..f79c8b0 100644
--- a/src/content/client/FollowMasterClient.ts
+++ b/src/content/client/FollowMasterClient.ts
@@ -35,7 +35,7 @@ export class FollowMasterClientImpl implements FollowMasterClient {
     this.postMessage({
       type: messages.FOLLOW_KEY_PRESS,
       key: key.key,
-      ctrlKey: key.ctrlKey || false,
+      ctrlKey: key.ctrl || false,
     });
   }
 
diff --git a/src/content/domains/Key.ts b/src/content/domains/Key.ts
index b25616e..669edfc 100644
--- a/src/content/domains/Key.ts
+++ b/src/content/domains/Key.ts
@@ -1,11 +1,3 @@
-export default interface Key {
-  key: string;
-  shiftKey?: boolean;
-  ctrlKey?: boolean;
-  altKey?: boolean;
-  metaKey?: boolean;
-}
-
 const modifiedKeyName = (name: string): string => {
   if (name === ' ') {
     return 'Space';
@@ -18,55 +10,84 @@ const modifiedKeyName = (name: string): string => {
   return name;
 };
 
-export const fromKeyboardEvent = (e: KeyboardEvent): Key => {
-  let key = modifiedKeyName(e.key);
-  let shift = e.shiftKey;
-  if (key.length === 1 && key.toUpperCase() === key.toLowerCase()) {
-    // make shift false for symbols to enable key bindings by symbold keys.
-    // But this limits key bindings by symbol keys with Shift (such as Shift+$>.
-    shift = false;
+export default class Key {
+  public readonly key: string;
+
+  public readonly shift: boolean;
+
+  public readonly ctrl: boolean;
+
+  public readonly alt: boolean;
+
+  public readonly meta: boolean;
+
+  constructor({ key, shift, ctrl, alt, meta }: {
+    key: string;
+    shift: boolean;
+    ctrl: boolean;
+    alt: boolean;
+    meta: boolean;
+  }) {
+    this.key = key;
+    this.shift = shift;
+    this.ctrl = ctrl;
+    this.alt = alt;
+    this.meta = meta;
   }
 
-  return {
-    key: modifiedKeyName(e.key),
-    shiftKey: shift,
-    ctrlKey: e.ctrlKey,
-    altKey: e.altKey,
-    metaKey: e.metaKey,
-  };
-};
+  static fromMapKey(str: string): Key {
+    if (str.startsWith('<') && str.endsWith('>')) {
+      let inner = str.slice(1, -1);
+      let shift = inner.includes('S-');
+      let base = inner.slice(inner.lastIndexOf('-') + 1);
+      if (shift && base.length === 1) {
+        base = base.toUpperCase();
+      } else if (!shift && base.length === 1) {
+        base = base.toLowerCase();
+      }
+      return new Key({
+        key: base,
+        shift: shift,
+        ctrl: inner.includes('C-'),
+        alt: inner.includes('A-'),
+        meta: inner.includes('M-'),
+      });
+    }
 
-export const fromMapKey = (key: string): Key => {
-  if (key.startsWith('<') && key.endsWith('>')) {
-    let inner = key.slice(1, -1);
-    let shift = inner.includes('S-');
-    let base = inner.slice(inner.lastIndexOf('-') + 1);
-    if (shift && base.length === 1) {
-      base = base.toUpperCase();
-    } else if (!shift && base.length === 1) {
-      base = base.toLowerCase();
+    return new Key({
+      key: str,
+      shift: str.toLowerCase() !== str,
+      ctrl: false,
+      alt: false,
+      meta: false,
+    });
+  }
+
+  static fromKeyboardEvent(e: KeyboardEvent): Key {
+    let key = modifiedKeyName(e.key);
+    let shift = e.shiftKey;
+    if (key.length === 1 && key.toUpperCase() === key.toLowerCase()) {
+      // make shift false for symbols to enable key bindings by symbold keys.
+      // But this limits key bindings by symbol keys with Shift
+      // (such as Shift+$>.
+      shift = false;
     }
-    return {
-      key: base,
-      shiftKey: inner.includes('S-'),
-      ctrlKey: inner.includes('C-'),
-      altKey: inner.includes('A-'),
-      metaKey: inner.includes('M-'),
-    };
+
+    return new Key({
+      key: modifiedKeyName(e.key),
+      shift: shift,
+      ctrl: e.ctrlKey,
+      alt: e.altKey,
+      meta: e.metaKey,
+    });
   }
-  return {
-    key: key,
-    shiftKey: key.toLowerCase() !== key,
-    ctrlKey: false,
-    altKey: false,
-    metaKey: false,
-  };
-};
 
-export const equals = (e1: Key, e2: Key): boolean => {
-  return e1.key === e2.key &&
-    e1.ctrlKey === e2.ctrlKey &&
-    e1.metaKey === e2.metaKey &&
-    e1.altKey === e2.altKey &&
-    e1.shiftKey === e2.shiftKey;
-};
+  equals(key: Key) {
+    return this.key === key.key &&
+        this.ctrl === key.ctrl &&
+        this.meta === key.meta &&
+        this.alt === key.alt &&
+        this.shift === key.shift;
+  }
+}
+
diff --git a/src/content/domains/KeySequence.ts b/src/content/domains/KeySequence.ts
index 6a05c2f..61ceab1 100644
--- a/src/content/domains/KeySequence.ts
+++ b/src/content/domains/KeySequence.ts
@@ -1,4 +1,4 @@
-import Key, * as keyUtils from './Key';
+import Key from './Key';
 
 export default class KeySequence {
   private keys: Key[];
@@ -24,7 +24,7 @@ export default class KeySequence {
       return false;
     }
     for (let i = 0; i < o.keys.length; ++i) {
-      if (!keyUtils.equals(this.keys[i], o.keys[i])) {
+      if (!this.keys[i].equals(o.keys[i])) {
         return false;
       }
     }
@@ -54,7 +54,7 @@ export const fromMapKeys = (keys: string): KeySequence => {
 
     return fromMapKeysRecursive(
       remainings.slice(nextPos),
-      mappedKeys.concat([keyUtils.fromMapKey(remainings.slice(0, nextPos))])
+      mappedKeys.concat([Key.fromMapKey(remainings.slice(0, nextPos))])
     );
   };
 
diff --git a/test/content/InputDriver.test.ts b/test/content/InputDriver.test.ts
index b9f2c28..b39312c 100644
--- a/test/content/InputDriver.test.ts
+++ b/test/content/InputDriver.test.ts
@@ -21,10 +21,10 @@ describe('InputDriver', () => {
   it('register callbacks', (done) => {
     driver.onKey((key: Key): boolean => {
       expect(key.key).to.equal('a');
-      expect(key.ctrlKey).to.be.true;
-      expect(key.shiftKey).to.be.false;
-      expect(key.altKey).to.be.false;
-      expect(key.metaKey).to.be.false;
+      expect(key.ctrl).to.be.true;
+      expect(key.shift).to.be.false;
+      expect(key.alt).to.be.false;
+      expect(key.meta).to.be.false;
       done();
       return true;
     });
@@ -68,15 +68,15 @@ describe('InputDriver', () => {
 
   it('propagates and stop handler chain', () => {
     let a = 0, b = 0, c = 0;
-    driver.onKey((key: Key): boolean => {
+    driver.onKey((_key: Key): boolean => {
       a++;
       return false;
     });
-    driver.onKey((key: Key): boolean => {
+    driver.onKey((_key: Key): boolean => {
       b++;
       return true;
     });
-    driver.onKey((key: Key): boolean => {
+    driver.onKey((_key: Key): boolean => {
       c++;
       return true;
     });
@@ -89,7 +89,7 @@ describe('InputDriver', () => {
   })
 
   it('does not invoke only meta keys', () => {
-    driver.onKey((key: Key): boolean=> {
+    driver.onKey((_key: Key): boolean=> {
       expect.fail();
       return false;
     });
@@ -115,7 +115,7 @@ describe('InputDriver', () => {
   it('ignores events from contenteditable elements', () => {
     let div = window.document.createElement('div');
     let driver = new InputDriver(div);
-    driver.onKey((key: Key): boolean => {
+    driver.onKey((_key: Key): boolean => {
       expect.fail();
       return false;
     });
diff --git a/test/content/domains/Key.test.ts b/test/content/domains/Key.test.ts
index b3f9fb6..8e62f80 100644
--- a/test/content/domains/Key.test.ts
+++ b/test/content/domains/Key.test.ts
@@ -1,137 +1,139 @@
-import Key, * as keys from '../../../src/content/domains/Key';
+import Key from '../../../src/content/domains/Key';
 import { expect } from 'chai'
 
 describe("Key", () => {
   describe('fromKeyboardEvent', () => {
     it('returns from keyboard input Ctrl+X', () => {
-      let k = keys.fromKeyboardEvent(new KeyboardEvent('keydown', {
+      let k = Key.fromKeyboardEvent(new KeyboardEvent('keydown', {
         key: 'x', shiftKey: false, ctrlKey: true, altKey: false, metaKey: true,
       }));
       expect(k.key).to.equal('x');
-      expect(k.shiftKey).to.be.false;
-      expect(k.ctrlKey).to.be.true;
-      expect(k.altKey).to.be.false;
-      expect(k.metaKey).to.be.true;
+      expect(k.shift).to.be.false;
+      expect(k.ctrl).to.be.true;
+      expect(k.alt).to.be.false;
+      expect(k.meta).to.be.true;
     });
 
     it('returns from keyboard input Shift+Esc', () => {
-      let k = keys.fromKeyboardEvent(new KeyboardEvent('keydown', {
+      let k = Key.fromKeyboardEvent(new KeyboardEvent('keydown', {
         key: 'Escape', shiftKey: true, ctrlKey: false, altKey: false, metaKey: true
       }));
       expect(k.key).to.equal('Esc');
-      expect(k.shiftKey).to.be.true;
-      expect(k.ctrlKey).to.be.false;
-      expect(k.altKey).to.be.false;
-      expect(k.metaKey).to.be.true;
+      expect(k.shift).to.be.true;
+      expect(k.ctrl).to.be.false;
+      expect(k.alt).to.be.false;
+      expect(k.meta).to.be.true;
     });
 
     it('returns from keyboard input Ctrl+$', () => {
       // $ required shift pressing on most keyboards
-      let k = keys.fromKeyboardEvent(new KeyboardEvent('keydown', {
+      let k = Key.fromKeyboardEvent(new KeyboardEvent('keydown', {
         key: '$', shiftKey: true, ctrlKey: true, altKey: false, metaKey: false
       }));
       expect(k.key).to.equal('$');
-      expect(k.shiftKey).to.be.false;
-      expect(k.ctrlKey).to.be.true;
-      expect(k.altKey).to.be.false;
-      expect(k.metaKey).to.be.false;
+      expect(k.shift).to.be.false;
+      expect(k.ctrl).to.be.true;
+      expect(k.alt).to.be.false;
+      expect(k.meta).to.be.false;
     });
 
     it('returns from keyboard input Crtl+Space', () => {
-      let k = keys.fromKeyboardEvent(new KeyboardEvent('keydown', {
+      let k = Key.fromKeyboardEvent(new KeyboardEvent('keydown', {
         key: ' ', shiftKey: false, ctrlKey: true, altKey: false, metaKey: false
       }));
       expect(k.key).to.equal('Space');
-      expect(k.shiftKey).to.be.false;
-      expect(k.ctrlKey).to.be.true;
-      expect(k.altKey).to.be.false;
-      expect(k.metaKey).to.be.false;
+      expect(k.shift).to.be.false;
+      expect(k.ctrl).to.be.true;
+      expect(k.alt).to.be.false;
+      expect(k.meta).to.be.false;
     });
   });
 
   describe('fromMapKey', () => {
     it('return for X', () => {
-      let key = keys.fromMapKey('x');
+      let key = Key.fromMapKey('x');
       expect(key.key).to.equal('x');
-      expect(key.shiftKey).to.be.false;
-      expect(key.ctrlKey).to.be.false;
-      expect(key.altKey).to.be.false;
-      expect(key.metaKey).to.be.false;
+      expect(key.shift).to.be.false;
+      expect(key.ctrl).to.be.false;
+      expect(key.alt).to.be.false;
+      expect(key.meta).to.be.false;
     });
 
     it('return for Shift+X', () => {
-      let key = keys.fromMapKey('X');
+      let key = Key.fromMapKey('X');
       expect(key.key).to.equal('X');
-      expect(key.shiftKey).to.be.true;
-      expect(key.ctrlKey).to.be.false;
-      expect(key.altKey).to.be.false;
-      expect(key.metaKey).to.be.false;
+      expect(key.shift).to.be.true;
+      expect(key.ctrl).to.be.false;
+      expect(key.alt).to.be.false;
+      expect(key.meta).to.be.false;
     });
 
     it('return for Ctrl+X', () => {
-      let key = keys.fromMapKey('<C-X>');
+      let key = Key.fromMapKey('<C-X>');
       expect(key.key).to.equal('x');
-      expect(key.shiftKey).to.be.false;
-      expect(key.ctrlKey).to.be.true;
-      expect(key.altKey).to.be.false;
-      expect(key.metaKey).to.be.false;
+      expect(key.shift).to.be.false;
+      expect(key.ctrl).to.be.true;
+      expect(key.alt).to.be.false;
+      expect(key.meta).to.be.false;
     });
 
     it('returns for Ctrl+Meta+X', () => {
-      let key = keys.fromMapKey('<C-M-X>');
+      let key = Key.fromMapKey('<C-M-X>');
       expect(key.key).to.equal('x');
-      expect(key.shiftKey).to.be.false;
-      expect(key.ctrlKey).to.be.true;
-      expect(key.altKey).to.be.false;
-      expect(key.metaKey).to.be.true;
+      expect(key.shift).to.be.false;
+      expect(key.ctrl).to.be.true;
+      expect(key.alt).to.be.false;
+      expect(key.meta).to.be.true;
     });
 
     it('returns for Ctrl+Shift+x', () => {
-      let key = keys.fromMapKey('<C-S-x>');
+      let key = Key.fromMapKey('<C-S-x>');
       expect(key.key).to.equal('X');
-      expect(key.shiftKey).to.be.true;
-      expect(key.ctrlKey).to.be.true;
-      expect(key.altKey).to.be.false;
-      expect(key.metaKey).to.be.false;
+      expect(key.shift).to.be.true;
+      expect(key.ctrl).to.be.true;
+      expect(key.alt).to.be.false;
+      expect(key.meta).to.be.false;
     });
 
     it('returns for Shift+Esc', () => {
-      let key = keys.fromMapKey('<S-Esc>');
+      let key = Key.fromMapKey('<S-Esc>');
       expect(key.key).to.equal('Esc');
-      expect(key.shiftKey).to.be.true;
-      expect(key.ctrlKey).to.be.false;
-      expect(key.altKey).to.be.false;
-      expect(key.metaKey).to.be.false;
+      expect(key.shift).to.be.true;
+      expect(key.ctrl).to.be.false;
+      expect(key.alt).to.be.false;
+      expect(key.meta).to.be.false;
     });
 
     it('returns for Ctrl+Esc', () => {
-      let key = keys.fromMapKey('<C-Esc>');
+      let key = Key.fromMapKey('<C-Esc>');
       expect(key.key).to.equal('Esc');
-      expect(key.shiftKey).to.be.false;
-      expect(key.ctrlKey).to.be.true;
-      expect(key.altKey).to.be.false;
-      expect(key.metaKey).to.be.false;
+      expect(key.shift).to.be.false;
+      expect(key.ctrl).to.be.true;
+      expect(key.alt).to.be.false;
+      expect(key.meta).to.be.false;
     });
 
     it('returns for Ctrl+Esc', () => {
-      let key = keys.fromMapKey('<C-Space>');
+      let key = Key.fromMapKey('<C-Space>');
       expect(key.key).to.equal('Space');
-      expect(key.shiftKey).to.be.false;
-      expect(key.ctrlKey).to.be.true;
-      expect(key.altKey).to.be.false;
-      expect(key.metaKey).to.be.false;
+      expect(key.shift).to.be.false;
+      expect(key.ctrl).to.be.true;
+      expect(key.alt).to.be.false;
+      expect(key.meta).to.be.false;
     });
   });
 
   describe('equals', () => {
-    expect(keys.equals(
-      { key: 'x', ctrlKey: true, },
-      { key: 'x', ctrlKey: true, },
-    )).to.be.true;
+    expect(new Key({
+        key: 'x', shift: false, ctrl: true, alt: false, meta: false,
+    }).equals(new Key({
+      key: 'x', shift: false, ctrl: true, alt: false, meta: false,
+    }))).to.be.true;
 
-    expect(keys.equals(
-      { key: 'X', shiftKey: true, },
-      { key: 'x', ctrlKey: true, },
-    )).to.be.false;
+    expect(new Key({
+      key: 'x', shift: false, ctrl: false, alt: false, meta: false,
+    }).equals(new Key({
+      key: 'X', shift: true, ctrl: false, alt: false, meta: false,
+    }))).to.be.false;
   });
 });
diff --git a/test/content/domains/KeySequence.test.ts b/test/content/domains/KeySequence.test.ts
index 7387c06..9afc360 100644
--- a/test/content/domains/KeySequence.test.ts
+++ b/test/content/domains/KeySequence.test.ts
@@ -1,48 +1,50 @@
 import KeySequence, * as utils from '../../../src/content/domains/KeySequence';
+import Key from '../../../src/content/domains/Key';
 import { expect } from 'chai'
 
 describe("KeySequence", () => {
   describe('#push', () => {
     it('append a key to the sequence', () => {
       let seq = KeySequence.from([]);
-      seq.push({ key: 'g' });
-      seq.push({ key: 'u', shiftKey: true });
+      seq.push(Key.fromMapKey('g'));
+      seq.push(Key.fromMapKey('<S-U>'));
 
       let array = seq.getKeyArray();
-      expect(array[0]).to.deep.equal({ key: 'g' });
-      expect(array[1]).to.deep.equal({ key: 'u', shiftKey: true });
+      expect(array[0].key).to.equal('g');
+      expect(array[1].key).to.equal('U');
+      expect(array[1].shift).to.be.true;
     })
   });
 
   describe('#startsWith', () => {
     it('returns true if the key sequence starts with param', () => {
       let seq = KeySequence.from([
-        { key: 'g' },
-        { key: 'u', shiftKey: true },
+        Key.fromMapKey('g'),
+        Key.fromMapKey('<S-U>'),
       ]);
 
       expect(seq.startsWith(KeySequence.from([
       ]))).to.be.true;
       expect(seq.startsWith(KeySequence.from([
-        { key: 'g' },
+        Key.fromMapKey('g'),
       ]))).to.be.true;
       expect(seq.startsWith(KeySequence.from([
-        { key: 'g' }, { key: 'u', shiftKey: true },
+        Key.fromMapKey('g'), Key.fromMapKey('<S-U>'),
       ]))).to.be.true;
       expect(seq.startsWith(KeySequence.from([
-        { key: 'g' }, { key: 'u', shiftKey: true }, { key: 'x' },
+        Key.fromMapKey('g'), Key.fromMapKey('<S-U>'), Key.fromMapKey('x'),
       ]))).to.be.false;
       expect(seq.startsWith(KeySequence.from([
-        { key: 'h' },
+        Key.fromMapKey('h'),
       ]))).to.be.false;
-    })
+    });
 
     it('returns true if the empty sequence starts with an empty sequence', () => {
       let seq = KeySequence.from([]);
 
       expect(seq.startsWith(KeySequence.from([]))).to.be.true;
       expect(seq.startsWith(KeySequence.from([
-        { key: 'h' },
+        Key.fromMapKey('h'),
       ]))).to.be.false;
     })
   });
@@ -52,21 +54,20 @@ describe("KeySequence", () => {
       let keyArray = utils.fromMapKeys('<S-Esc>').getKeyArray();
       expect(keyArray).to.have.lengthOf(1);
       expect(keyArray[0].key).to.equal('Esc');
-      expect(keyArray[0].shiftKey).to.be.true;
+      expect(keyArray[0].shift).to.be.true;
     });
 
     it('returns mapped keys for a<C-B><A-C>d<M-e>', () => {
       let keyArray = utils.fromMapKeys('a<C-B><A-C>d<M-e>').getKeyArray();
       expect(keyArray).to.have.lengthOf(5);
       expect(keyArray[0].key).to.equal('a');
-      expect(keyArray[1].ctrlKey).to.be.true;
+      expect(keyArray[1].ctrl).to.be.true;
       expect(keyArray[1].key).to.equal('b');
-      expect(keyArray[2].altKey).to.be.true;
+      expect(keyArray[2].alt).to.be.true;
       expect(keyArray[2].key).to.equal('c');
       expect(keyArray[3].key).to.equal('d');
-      expect(keyArray[4].metaKey).to.be.true;
+      expect(keyArray[4].meta).to.be.true;
       expect(keyArray[4].key).to.equal('e');
     });
   })
-
 });
diff --git a/test/content/repositories/KeymapRepository.test.ts b/test/content/repositories/KeymapRepository.test.ts
index 34704d9..8f0be67 100644
--- a/test/content/repositories/KeymapRepository.test.ts
+++ b/test/content/repositories/KeymapRepository.test.ts
@@ -1,5 +1,6 @@
 import KeymapRepository, { KeymapRepositoryImpl }
   from '../../../src/content/repositories/KeymapRepository';
+import Key from '../../../src/content/domains/Key'
 import { expect } from 'chai';
 
 describe('KeymapRepositoryImpl', () => {
@@ -11,24 +12,25 @@ describe('KeymapRepositoryImpl', () => {
 
   describe('#enqueueKey()', () => {
     it('enqueues keys', () => {
-      sut.enqueueKey({ key: 'a' });
-      sut.enqueueKey({ key: 'b' });
-      let sequence = sut.enqueueKey({ key: 'c' });
-
-      expect(sequence.getKeyArray()).deep.equals([
-        { key: 'a' }, { key: 'b' }, { key: 'c' },
-      ]);
+      sut.enqueueKey(Key.fromMapKey('a');
+      sut.enqueueKey(Key.fromMapKey('b');
+      let sequence = sut.enqueueKey(Key.fromMapKey('c'));
+
+      let keys = sequence.getKeyArray();
+      expect(keys[0].equals(Key.fromMapKey('a'))).to.be.true;
+      expect(keys[1].equals(Key.fromMapKey('b'))).to.be.true;
+      expect(keys[2].equals(Key.fromMapKey('c'))).to.be.true;
     });
   });
 
   describe('#clear()', () => {
     it('clears keys', () => {
-      sut.enqueueKey({ key: 'a' });
-      sut.enqueueKey({ key: 'b' });
-      sut.enqueueKey({ key: 'c' });
+      sut.enqueueKey(Key.fromMapKey('a');
+      sut.enqueueKey(Key.fromMapKey('b');
+      sut.enqueueKey(Key.fromMapKey('c');
       sut.clear();
 
-      let sequence = sut.enqueueKey({ key: 'a' });
+      let sequence = sut.enqueueKey(Key.fromMapKey('a'));
       expect(sequence.length()).to.equal(1);
     });
   });