diff --git a/backend/app/controllers/posts_controller.rb b/backend/app/controllers/posts_controller.rb
index bcfc0c4..39d2ee1 100644
--- a/backend/app/controllers/posts_controller.rb
+++ b/backend/app/controllers/posts_controller.rb
@@ -18,13 +18,13 @@ class PostsController < ApplicationController
     else
       @posts = Post.all
     end
-    render json: @posts
+    render json: @posts.as_json(include: { tags: { only: [:id, :name, :category] } })
   end
 
   # GET /posts/1
   def show
     @post = Post.includes(:tags).find(params[:id])
-    render json: @post.as_json(include: { tags: { only: [:id, :name] } })
+    render json: @post.as_json(include: { tags: { only: [:id, :name, :category] } })
   end
 
   # POST /posts
diff --git a/frontend/src/App.tsx b/frontend/src/App.tsx
index 8b8803c..c27eb2b 100644
--- a/frontend/src/App.tsx
+++ b/frontend/src/App.tsx
@@ -1,4 +1,4 @@
-import React from 'react'
+import React, { useEffect, useState } from 'react'
 import { BrowserRouter as Router, Route, Routes } from 'react-router-dom'
 import HomePage from './pages/HomePage'
 import TagPage from './pages/TagPage'
@@ -7,28 +7,41 @@ import TagSidebar from './components/TagSidebar'
 import PostPage from './pages/PostPage'
 import PostDetailPage from './pages/PostDetailPage'
 
+type Tag = { id:        number
+             name:      string
+             category:  string }
+
+type Post = { id:         number
+              url:        string
+              title:      string
+              thumbnail:  string
+              tags:       Tag[] }
+
+
 const App = () => {
+  const [posts, setPosts] = useState<Post[]> ([])
+
+  useEffect (() => {
+    alert ('このサイトはまだ作りかけです!!!!\n出てけ!!!!!!!!!!!!!!!!!!!!')
+  }, [])
+
   return (
-    <Router>
-      <div className="flex flex-col h-screen w-screen">
-        <TopNav />
-        <div className="flex flex-1">
-          <Routes>
-            <Route path="/posts/:postId" element={<TagSidebar />} />
-            <Route path="*" element={<TagSidebar />} />
-          </Routes>
-          <main className="flex-1 overflow-y-auto p-4">
-            <Routes>
-              <Route path="/" element={<PostPage />} />
-              <Route path="/posts" element={<PostPage />} />
-              <Route path="/posts/:id" element={<PostDetailPage />} />
-              <Route path="/tags/:tag" element={<TagPage />} />
-            </Routes>
-          </main>
+      <Router>
+        <div className="flex flex-col h-screen w-screen">
+          <TopNav />
+          <div className="flex flex-1">
+            <TagSidebar posts={posts} setPosts={setPosts} />
+            <main className="flex-1 overflow-y-auto p-4">
+              <Routes>
+                <Route path="/posts/:id" element={<PostDetailPage posts={posts} setPosts={setPosts} />} />
+                <Route path="/tags/:tag" element={<TagPage />} />
+                <Route path="*" element={<PostPage posts={posts} setPosts={setPosts} />} />
+              </Routes>
+            </main>
+          </div>
         </div>
-      </div>
-    </Router>
-  )
+      </Router>)
 }
 
+
 export default App
diff --git a/frontend/src/components/NicoViewer.tsx b/frontend/src/components/NicoViewer.tsx
index 8f1aee1..8636c53 100644
--- a/frontend/src/components/NicoViewer.tsx
+++ b/frontend/src/components/NicoViewer.tsx
@@ -15,23 +15,23 @@ const NicoViewer: React.FC = (props: Props) => {
   const iframeRef = useRef<HTMLIFrameElement> (null)
   const [screenWidth, setScreenWidth] = useState<CSSProperties['width']> ()
   const [screenHeight, setScreenHeight] = useState<CSSProperties['height']> ()
-  const [isLandscape, setIsLandScape] = useState<boolean> (false)
-  const [isFullScreen, setIsFullScreen] = useState<boolean> (false)
+  const [landscape, setLandscape] = useState<boolean> (false)
+  const [fullScreen, setFullScreen] = useState<boolean> (false)
 
   const src = `https://embed.nicovideo.jp/watch/${id}?persistence=1&oldScript=1&referer=&from=0&allowProgrammaticFullScreen=1`;
 
-  const styleFullScreen: CSSProperties = isFullScreen ? {
+  const styleFullScreen: CSSProperties = fullScreen ? {
     top: 0,
-    left: isLandscape ? 0 : '100%',
+    left: landscape ? 0 : '100%',
     position: 'fixed',
     width: screenWidth,
     height: screenHeight,
     zIndex: 2147483647,
     maxWidth: 'none',
     transformOrigin: '0% 0%',
-    transform: isLandscape ? 'none' : 'rotate(90deg)',
+    transform: landscape ? 'none' : 'rotate(90deg)',
     WebkitTransformOrigin: '0% 0%',
-    WebkitTransform: isLandscape ? 'none' : 'rotate(90deg)',
+    WebkitTransform: landscape ? 'none' : 'rotate(90deg)',
   } : {};
 
   const margedStyle = {
@@ -45,38 +45,40 @@ const NicoViewer: React.FC = (props: Props) => {
     const onMessage = (event: MessageEvent<any>) => {
       if (!iframeRef.current || event.source !== iframeRef.current.contentWindow) return;
       if (event.data.eventName === 'enterProgrammaticFullScreen') {
-        setIsFullScreen(true);
+        setFullScreen(true);
       } else if (event.data.eventName === 'exitProgrammaticFullScreen') {
-        setIsFullScreen(false);
+        setFullScreen(false);
       }
     };
 
-    window.addEventListener('message', onMessage);
+    addEventListener('message', onMessage);
 
     return () => {
-      window.removeEventListener('message', onMessage);
+      removeEventListener('message', onMessage);
     };
   }, []);
 
   useLayoutEffect(() => {
-    if (!isFullScreen) return;
+    if (!(fullScreen))
+      return
 
-    const initialScrollX = window.scrollX;
-    const initialScrollY = window.scrollY;
-    let timer: NodeJS.Timeout;
-    let ended = false;
+    const initialScrollX = window.scrollX
+    const initialScrollY = window.scrollY
+    let timer: NodeJS.Timeout
+    let ended = false
 
     const pollingResize = () => {
-      if (ended) return;
+      if (ended)
+        return
 
-      const isLandscape = window.innerWidth >= window.innerHeight;
-      const windowWidth = `${isLandscape ? window.innerWidth : window.innerHeight}px`;
-      const windowHeight = `${isLandscape ? window.innerHeight : window.innerWidth}px`;
+      const landscape = window.innerWidth >= window.innerHeight
+      const windowWidth = `${landscape ? window.innerWidth : window.innerHeight}px`
+      const windowHeight = `${landscape ? window.innerHeight : window.innerWidth}px`
 
-      setIsLandScape(isLandscape);
-      setScreenWidth(windowWidth);
-      setScreenHeight(windowHeight);
-      timer = setTimeout(startPollingResize, 200);
+      setLandScape (Landscape)
+      setScreenWidth (windowWidth)
+      setScreenHeight (windowHeight)
+      timer = setTimeout (startPollingResize, 200)
     }
 
     const startPollingResize = () => {
@@ -94,12 +96,13 @@ const NicoViewer: React.FC = (props: Props) => {
       ended = true;
       window.scrollTo(initialScrollX, initialScrollY);
     };
-  }, [isFullScreen]);
+  }, [fullScreen]);
 
   useEffect(() => {
-    if (!isFullScreen) return;
-    window.scrollTo(0, 0);
-  }, [screenWidth, screenHeight, isFullScreen]);
+    if (!(fullScreen))
+      return
+    scrollTo (0, 0)
+  }, [screenWidth, screenHeight, fullScreen])
 
   return <iframe ref={iframeRef}
                  src={src}
diff --git a/frontend/src/components/TagSearch.tsx b/frontend/src/components/TagSearch.tsx
index ac7b723..f177efa 100644
--- a/frontend/src/components/TagSearch.tsx
+++ b/frontend/src/components/TagSearch.tsx
@@ -7,10 +7,8 @@ import { API_BASE_URL } from '../config'
 const TagSearch: React.FC = () => {
   const navigate = useNavigate ()
   const location = useLocation ()
-  const query = new URLSearchParams (location.search)
-  const tagsQuery = query.get ('tags') ?? ''
 
-  const [search, setSearch] = useState (tagsQuery)
+  const [search, setSearch] = useState ('')
 
   const handleKeyDown = (e: React.KeyboardEvent<HTMLInputElement>) => {
     if (e.key === 'Enter' && search.length > 0)
@@ -18,6 +16,12 @@ const TagSearch: React.FC = () => {
                 { replace: true })
   }
 
+  useEffect (() => {
+    const query = new URLSearchParams (location.search)
+    const tagsQuery = query.get ('tags') ?? ''
+    setSearch (tagsQuery)
+  }, [location.search])
+
   return (
     <input
       type="text"
diff --git a/frontend/src/components/TagSidebar.tsx b/frontend/src/components/TagSidebar.tsx
index 4b2bd8b..16db20a 100644
--- a/frontend/src/components/TagSidebar.tsx
+++ b/frontend/src/components/TagSidebar.tsx
@@ -4,65 +4,86 @@ import { Link, useParams } from 'react-router-dom'
 import { API_BASE_URL } from '../config'
 import TagSearch from './TagSearch'
 
-type Tag = { id:    number
-             name:  string }
+type Tag = { id:        number
+             name:      string
+             category:  string }
+
 type TagByCategory = { [key: string]: Tag[] }
-type OriginalTag = { id: number
-                     name: string
-                     category: string }
+
+type OriginalTag = { id:        number
+                     name:      string
+                     category:  string }
+
+type Post = { id:         number
+              url:        string
+              title:      string
+              thumbnail:  string
+              tags:       Tag[] }
+
+type Props = { posts:     Post[]
+               setPosts:  (posts: Post[]) => void }
+
 
 const tagNameMap: { [key: string]: string } = {
     general:    '一般',
     deerjikist: 'ニジラー',
     nico:       'ニコニコタグ' }
 
-const TagSidebar: React.FC = () => {
-  const { postId } = useParams<{ postId?: number }> ()
+const TagSidebar: React.FC = (props: Props) => {
+  const { posts, setPosts } = props
+
   const [tags, setTags] = useState<TagByCategory> ({ })
+  const [tagsCounts, setTagsCounts] = useState<{ [key: id]: number }> ({ })
 
-  useEffect(() => {
+  useEffect (() => {
     const fetchTags = async () => {
-      try {
-        const response = await axios.get (`${API_BASE_URL}/tags`
-            + (postId ? `?post=${ postId }` : ''))
-        const tagsTmp: TagByCategory = { }
-        for (const tag of response.data)
+      try
+      {
+        let tagsTmp: TagByCategory = { }
+        let tagsCountsTmp: { [key: id]: number } = { }
+        for (const post of posts)
           {
-            if (!(tag.category in tagsTmp))
-              tagsTmp[tag.category] = []
-            tagsTmp[tag.category].push ({ id: tag.id, name: tag.name })
+            for (const tag of post.tags)
+              {
+                if (!(tag.category in tagsTmp))
+                  tagsTmp[tag.category] = []
+                tagsTmp[tag.category].push (tag)
+                if (!(tag.id in tagsCountsTmp))
+                  tagsCountsTmp[tag.id] = 0
+                ++tagsCountsTmp[tag.id]
+              }
           }
+        for (const cat of Object.keys (tagsTmp))
+          tagsTmp[cat].sort ((tagA, tagB) => tagA.name < tagB.name ? -1 : 1)
         setTags (tagsTmp)
-      } catch (error) {
-        console.error('Failed to fetch tags:', error)
+        setTagsCounts (tagsCountsTmp)
+      }
+      catch (error)
+      {
+        console.error ('Failed to fetch tags:', error)
       }
     }
 
-    fetchTags()
-  }, [postId])
+    fetchTags ()
+  }, [posts])
 
   return (
       <div className="w-64 bg-gray-100 p-4 border-r border-gray-200 h-full">
         <TagSearch />
-        {['general', 'deerjikist', 'nico'].map (cat => (cat in tags) ? (
-            <>
-              <h2>{tagNameMap[cat]}</h2>
-              <ul>
-                {tags[cat].map (tag => (
-                    <li key={tag.id} className="mb-2">
-                      <Link
-                        to={`/posts?${ (new URLSearchParams ({ tags: tag.name })).toString () }`}
-                        className="text-blue-600 hover:underline"
-                      >
-                        {tag.name}
-                      </Link>
-                    </li>
-                    ))}
-              </ul>
-            </>
-            ) : <></>)}
-      </div>
-      )
+        {['general', 'deerjikist', 'nico'].map (cat => cat in tags && <>
+            <h2>{tagNameMap[cat]}</h2>
+            <ul>
+              {tags[cat].map (tag => (
+                  <li key={tag.id} className="mb-2">
+                    <Link to={`/posts?${ (new URLSearchParams ({ tags: tag.name })).toString () }`}
+                          className="text-blue-600 hover:underline">
+                      {tag.name}
+                    </Link>
+                    {posts.length > 1 && <span className="ml-1">{tagsCounts[tag.id]}</span>}
+                  </li>))}
+            </ul>
+            </>)}
+      </div>)
 }
 
 export default TagSidebar
diff --git a/frontend/src/components/TopNav.tsx b/frontend/src/components/TopNav.tsx
index d3466f0..89fe2c4 100644
--- a/frontend/src/components/TopNav.tsx
+++ b/frontend/src/components/TopNav.tsx
@@ -1,20 +1,18 @@
 import React from "react"
+import { Link } from 'react-router-dom'
 
-const TopNav: React.FC = () => {
-  return (
+const TopNav: React.FC = () => (
     <nav className="bg-gray-800 text-white p-3 flex justify-between items-center w-full">
       <div className="flex items-center gap-4">
-        <a href="/" className="text-xl font-bold text-orange-500">ぼざクリ タグ広場</a>
-        <a href="/" className="hover:text-orange-500">広場</a>
-        <a href="/deerjikists" className="hover:text-orange-500">ニジラー</a>
-        <a href="/tags" className="hover:text-orange-500">タグ</a>
-        <a href="/wiki" className="hover:text-orange-500">Wiki</a>
+        <Link to="/" className="text-xl font-bold text-orange-500">ぼざクリ タグ広場</Link>
+        <Link to="/posts" className="hover:text-orange-500">広場</Link>
+        <Link to="/deerjikists" className="hover:text-orange-500">ニジラー</Link>
+        <Link to="/tags" className="hover:text-orange-500">タグ</Link>
+        <Link to="/wiki" className="hover:text-orange-500">Wiki</Link>
       </div>
       <div className="ml-auto pr-4">
-        <a href="/login" className="hover:text-orange-500">ログイン</a>
+        <Link to="/login" className="hover:text-orange-500">ログイン</Link>
       </div>
-    </nav>
-  )
-}
+    </nav>)
 
 export default TopNav
diff --git a/frontend/src/pages/PostDetailPage.tsx b/frontend/src/pages/PostDetailPage.tsx
index 12b7f5f..039d97f 100644
--- a/frontend/src/pages/PostDetailPage.tsx
+++ b/frontend/src/pages/PostDetailPage.tsx
@@ -4,15 +4,23 @@ import axios from 'axios'
 import { API_BASE_URL, SITE_TITLE } from '../config'
 import NicoViewer from '../components/NicoViewer'
 
+type Tag = { id:        number
+             name:      string
+             category:  string }
+
 type Post = { id:         number
               url:        string
               title:      string
               thumbnail:  string
-              tags:       { name: string }[] }
+              tags:       Tag[] }
+
+type Props = { posts:     Post[]
+               setPosts:  (posts: Post[]) => void }
+
 
-const PostDetailPage = () => {
+const PostDetailPage = (props: Props) => {
+  const { posts, setPosts } = props
   const { id } = useParams ()
-  const [post, setPost] = useState<Post | null> (null)
 
   const location = useLocation ()
 
@@ -20,28 +28,36 @@ const PostDetailPage = () => {
     if (!(id))
       return
     void (axios.get (`/api/posts/${ id }`)
-          .then (res => setPost (res.data))
+          .then (res => setPosts ([res.data]))
           .catch (err => console.error ('うんち!', err)))
   }, [id])
 
-  if (!(post))
+  if (!(posts.length))
     return <div>Loading...</div>
 
-  document.title = `${ post.url } | ${ SITE_TITLE }`
+  const post = posts[0]
+
+  document.title = `${ post.title || post.url } | ${ SITE_TITLE }`
 
   const url = new URL (post.url)
 
   return (
       <div className="p-4">
-        {url.hostname.split ('.').slice (-2).join ('.') === 'nicovideo.jp' ? (
-            <NicoViewer id={url.pathname.match (/(?<=\/watch\/)[a-zA-Z0-9]+?(?=\/|$)/)[0]}
-                        width="640"
-                        height="360" />
-            ) : (
-            <img src={post.thumbnail} alt={post.url} className="mb-4 w-full" />
-            )}
-      </div>
-      )
+        {(() => {
+          if (url.hostname.split ('.').slice (-2).join ('.') === 'nicovideo.jp')
+            {
+              return (
+                  <NicoViewer
+                    id={url.pathname.match (
+                          /(?<=\/watch\/)[a-zA-Z0-9]+?(?=\/|$)/)[0]}
+                    width="640"
+                    height="360" />)
+            }
+          else
+            return <img src={post.thumbnail} alt={post.url} className="mb-4 w-full" />
+        }) ()}
+      </div>)
 }
 
+
 export default PostDetailPage
diff --git a/frontend/src/pages/PostPage.tsx b/frontend/src/pages/PostPage.tsx
index be95f6d..605e7b6 100644
--- a/frontend/src/pages/PostPage.tsx
+++ b/frontend/src/pages/PostPage.tsx
@@ -3,8 +3,22 @@ import { Link, useLocation } from 'react-router-dom'
 import axios from 'axios'
 import { API_BASE_URL, SITE_TITLE } from '../config'
 
-const PostPage = () => {
-  const [posts, setPosts] = useState([])
+type Tag = { id:        number
+             name:      string
+             category:  string }
+
+type Post = { id:         number
+              url:        string
+              title:      string
+              thumbnail:  string
+              tags:       Tag[] }
+
+type Props = { posts:     Post[]
+               setPosts:  (posts: Post[]) => void }
+
+
+const PostPage = (props: Props) => {
+  const { posts, setPosts } = props
 
   const location = useLocation ()
   const query = new URLSearchParams (location.search)
@@ -19,35 +33,34 @@ const PostPage = () => {
 
   useEffect(() => {
     const fetchPosts = async () => {
-      try {
-        const response = await axios.get(`${ API_BASE_URL }/posts`, {
+      try
+      {
+        const res = await axios.get (`${ API_BASE_URL }/posts`, {
             params: { tags:   tags.join (','),
                       match:  (anyFlg ? 'any' : 'all') } })
-        setPosts(response.data)
-      } catch (error) {
-        console.error('Failed to fetch posts:', error)
-        setPosts([])
+        setPosts (res.data)
+      }
+      catch (error)
+      {
+        console.error ('Failed to fetch posts:', error)
+        setPosts ([])
       }
     }
     fetchPosts()
   }, [location.search])
 
   return (
-    <div className="flex flex-wrap gap-4 p-4">
-      {posts.map (post => (
-        <Link
-          to={`/posts/${ post.id }`}
-          key={post.id}
-          className="w-40 h-40 overflow-hidden rounded-lg shadow-md hover:shadow-lg"
-        >
-          <img
-            src={post.thumbnail}
-            className="object-none w-full h-full"
-          />
-        </Link>
-      ))}
-    </div>
-  )
+      <div className="flex flex-wrap gap-4 p-4">
+        {posts.map (post => (
+          <Link to={`/posts/${ post.id }`}
+                key={post.id}
+                className="w-40 h-40 overflow-hidden rounded-lg shadow-md hover:shadow-lg">
+            <img src={post.thumbnail ?? post.thumbnail_base}
+                 className="object-none w-full h-full" />
+          </Link>
+        ))}
+      </div>)
 }
 
+
 export default PostPage