diff --git a/src/lib/db/store.spec.ts b/src/lib/db/store.spec.ts
index 1f1b9aa74e..8fc09d020c 100644
--- a/src/lib/db/store.spec.ts
+++ b/src/lib/db/store.spec.ts
@@ -1,7 +1,7 @@
 import { createDbStoreCreator, getStorageDataList } from './store'
 import { MemoryLiteStorage } from 'ltstrg'
 import { renderHook, act } from '@testing-library/react-hooks'
-import { NoteStorage } from './types'
+import { NoteStorage, NoteDoc } from './types'
 import { getFolderId } from './utils'
 import { RouterProvider } from '../router'
 
@@ -201,4 +201,110 @@ describe('DbStore', () => {
 
     // TODO: routing test when current folder or current folder's parent folder is deleted.
   })
+
+  describe('#createNote', () => {
+    it('creates a note and registers in the map', async () => {
+      // Given
+      const { result } = prepareDbStore()
+      let storage: NoteStorage
+      let noteDoc: NoteDoc | undefined
+      await act(async () => {
+        await result.current.initialize()
+        storage = await result.current.createStorage('test')
+        await result.current.createFolder(storage.id, '/test')
+
+        // When
+        noteDoc = await result.current.createNote(storage.id, {
+          title: 'testNote'
+        })
+      })
+
+      // Then
+      expect(result.current.storageMap[storage!.id]!.noteMap).toEqual({
+        [noteDoc!._id]: expect.objectContaining({ title: 'testNote' })
+      })
+    })
+
+    it('creates a note and register its tag', async () => {
+      // Given
+      const { result } = prepareDbStore()
+      let storage: NoteStorage
+      let noteDoc: NoteDoc | undefined
+      await act(async () => {
+        await result.current.initialize()
+        storage = await result.current.createStorage('test')
+        await result.current.createFolder(storage.id, '/test')
+
+        // When
+        noteDoc = await result.current.createNote(storage.id, {
+          title: 'testNote',
+          tags: ['testTag']
+        })
+      })
+
+      // Then
+      expect(
+        result.current.storageMap[storage!.id]!.tagMap[noteDoc!.tags[0]]!
+          .noteIdSet
+      ).toMatchObject(new Set([noteDoc!._id]))
+    })
+  })
+
+  describe('#updateNote', () => {
+    it('update a Note and handle tag removal', async () => {
+      // Given
+      const { result } = prepareDbStore()
+      let storage: NoteStorage
+      let noteDoc: NoteDoc | undefined
+      await act(async () => {
+        await result.current.initialize()
+        storage = await result.current.createStorage('test')
+        await result.current.createFolder(storage.id, '/test')
+        noteDoc = await result.current.createNote(storage.id, {
+          title: 'testNote',
+          tags: ['tag1', 'tag2']
+        })
+
+        // When
+        noteDoc = await result.current.updateNote(storage.id, noteDoc!._id, {
+          tags: ['tag2']
+        })
+      })
+
+      // Then
+      expect(
+        result.current.storageMap[storage!.id]!.tagMap['tag1']!.noteIdSet.size
+      ).toEqual(0)
+    })
+
+    it('update a Note and handle tag addition', async () => {
+      // Given
+      const { result } = prepareDbStore()
+      let storage: NoteStorage
+      let noteDoc: NoteDoc | undefined
+      await act(async () => {
+        await result.current.initialize()
+        storage = await result.current.createStorage('test')
+        await result.current.createFolder(storage.id, '/test')
+        noteDoc = await result.current.createNote(storage.id, {
+          title: 'testNote',
+          tags: ['tag1']
+        })
+        await result.current.createNote(storage.id, {
+          title: 'testNote',
+          tags: ['tag2']
+        })
+
+        // When
+        noteDoc = await result.current.updateNote(storage.id, noteDoc!._id, {
+          tags: ['tag1', 'tag2']
+        })
+      })
+
+      // Then
+      expect(
+        result.current.storageMap[storage!.id]!.tagMap['tag2']!.noteIdSet.size
+      ).toEqual(2)
+    })
+  })
 })
diff --git a/src/lib/db/store.ts b/src/lib/db/store.ts
index bc50f4d95f..2a1a1fa0d5 100644
--- a/src/lib/db/store.ts
+++ b/src/lib/db/store.ts
@@ -4,7 +4,8 @@ import {
   ObjectMap,
   NoteDoc,
   NoteDocEditibleProps,
-  PopulatedFolderDoc
+  PopulatedFolderDoc,
+  PopulatedTagDoc
 } from './types'
 import { useState, useCallback } from 'react'
 import { createStoreContext } from '../utils/context'
@@ -23,6 +24,8 @@ import { produce } from 'immer'
 import { useRouter } from '../router'
 import { values } from '../db/utils'
 import { storageDataListKey } from '../localStorageKeys'
+import { TAG_ID_PREFIX } from './consts'
+import { difference } from 'ramda'
 
 export interface DbStore {
   initialized: boolean
@@ -213,6 +216,7 @@ export function createDbStoreCreator(
                 parentFolderPathnamesToCheck
               )
             : []
+
         const folder: PopulatedFolderDoc =
           storage.folderMap[noteDoc.folderPathname] == null
             ? ({
@@ -228,7 +232,28 @@ export function createDbStoreCreator(
                 ])
               }
 
-        // TODO: Reflect tags
+        const modifiedTags = ((await Promise.all(
+          noteDoc.tags.map(async tag => {
+            if (storage.tagMap[tag] == null) {
+              return {
+                ...(await storage.db.getTag(tag)!),
+                noteIdSet: new Set([noteDoc._id])
+              } as PopulatedTagDoc
+            } else {
+              return {
+                ...storage.tagMap[tag]!,
+                noteIdSet: new Set([
+                  ...storage.tagMap[tag]!.noteIdSet.values(),
+                  noteDoc._id
+                ])
+              }
+            }
+          })
+        )) as PopulatedTagDoc[]).reduce((acc, tag) => {
+          acc[tag._id.replace(TAG_ID_PREFIX, '')] = tag
+          return acc
+        }, {})
+
         setStorageMap(
           produce((draft: ObjectMap<NoteStorage>) => {
             draft[storageId]!.noteMap[noteDoc._id] = noteDoc
@@ -241,9 +266,12 @@ export function createDbStoreCreator(
               }
             })
             draft[storageId]!.folderMap[noteDoc.folderPathname] = folder
+            draft[storageId]!.tagMap = {
+              ...storage.tagMap,
+              ...modifiedTags
+            }
           })
         )
-
         return noteDoc
       },
       [storageMap]
@@ -288,7 +316,41 @@ export function createDbStoreCreator(
                 ])
               }
 
-        // TODO: Reflect tags
+        const removedTags: ObjectMap<PopulatedTagDoc> = difference(
+          storage.noteMap[noteDoc._id]!.tags,
+          noteDoc.tags
+        ).reduce((acc, tag) => {
+          const newNoteIdSet = new Set(storage.tagMap[tag]!.noteIdSet)
+          newNoteIdSet.delete(noteDoc._id)
+          acc[tag] = {
+            ...storage.tagMap[tag]!,
+            noteIdSet: newNoteIdSet
+          }
+          return acc
+        }, {})
+
+        const modifiedTags: ObjectMap<PopulatedTagDoc> = ((await Promise.all(
+          noteDoc.tags.map(async tag => {
+            if (storage.tagMap[tag] == null) {
+              return {
+                ...(await storage.db.getTag(tag)!),
+                noteIdSet: new Set([noteDoc._id])
+              } as PopulatedTagDoc
+            } else {
+              return {
+                ...storage.tagMap[tag]!,
+                noteIdSet: new Set([
+                  ...storage.tagMap[tag]!.noteIdSet.values(),
+                  noteDoc._id
+                ])
+              }
+            }
+          })
+        )) as PopulatedTagDoc[]).reduce((acc, tag) => {
+          acc[tag._id.replace(TAG_ID_PREFIX, '')] = tag
+          return acc
+        }, {})
+
         setStorageMap(
           produce((draft: ObjectMap<NoteStorage>) => {
             draft[storageId]!.noteMap[noteDoc._id] = noteDoc
@@ -301,6 +363,11 @@ export function createDbStoreCreator(
               }
             })
             draft[storageId]!.folderMap[noteDoc.folderPathname] = folder
+            draft[storageId]!.tagMap = {
+              ...storage.tagMap,
+              ...removedTags,
+              ...modifiedTags
+            }
           })
         )
 
diff --git a/webpack.config.ts b/webpack.config.ts
index e443db2d7b..56bb01000e 100644
--- a/webpack.config.ts
+++ b/webpack.config.ts
@@ -6,7 +6,10 @@ import ErrorOverlayPlugin from 'error-overlay-webpack-plugin'
 import dotenv from 'dotenv'
 import CopyPlugin from 'copy-webpack-plugin'
 
-const { parsed } = dotenv.config()
+let { parsed } = dotenv.config()
+if (parsed == null) {
+  parsed = {}
+}
 
 module.exports = {
   entry: [