diff --git a/backend/spec/requests/posts_spec.rb b/backend/spec/requests/posts_spec.rb
index 4366a64..a65a935 100644
--- a/backend/spec/requests/posts_spec.rb
+++ b/backend/spec/requests/posts_spec.rb
@@ -15,11 +15,11 @@ RSpec.describe 'Posts API', type: :request do
       expect(response).to have_http_status(:ok)
 
       expect(json).to have_key('posts')
-      expect(json['posts']).to be_a(Array)
+      expect(json['posts']).to be_an(Array)
       expect(json['posts']).not_to be_empty
 
       tags = json['posts'][0]['tags']
-      expect(tags).to be_a(Array)
+      expect(tags).to be_an(Array)
       expect(tags).not_to be_empty
 
       expect(tags[0]).to have_key('name')
diff --git a/backend/spec/requests/tags_spec.rb b/backend/spec/requests/tags_spec.rb
index 255a300..7e26538 100644
--- a/backend/spec/requests/tags_spec.rb
+++ b/backend/spec/requests/tags_spec.rb
@@ -11,23 +11,50 @@ RSpec.describe 'Tags API', type: :request do
       get '/tags'
 
       expect(response).to have_http_status(:ok)
-      json = JSON.parse(response.body)
 
-      expect(json).to be_a(Array)
+      expect(json).to be_an(Array)
       expect(json).not_to be_empty
       expect(json[0]).to have_key('name')
       expect(json.map { |t| t['name'] }).to include('spec_tag')
     end
   end
 
+  describe 'GET /tags/:id' do
+    subject(:request) do
+      get "/tags/#{ tag_id }"
+    end
+
+    let(:tag_id) { tag.id }
+
+    context 'when tag exists' do
+      it 'returns tag with name' do
+        request
+        expect(response).to have_http_status(:ok)
+
+        expect(json).to include(
+            'id'        => tag.id,
+            'name'      => 'spec_tag',
+            'category'  => 'general')
+      end
+    end
+
+    context 'when tag does not exist' do
+      let(:tag_id) { 9_999_999 }
+
+      it 'returns 404' do
+        request
+        expect(response).to have_http_status(:not_found)
+      end
+    end
+  end
+
   describe 'GET /tags/autocomplete' do
     it 'returns matching tags by q' do
       get '/tags/autocomplete', params: { q: 'spec' }
 
       expect(response).to have_http_status(:ok)
-      json = JSON.parse(response.body)
 
-      expect(json).to be_a(Array)
+      expect(json).to be_an(Array)
       expect(json.map { |t| t['name'] }).to include('spec_tag')
     end
   end
@@ -37,7 +64,6 @@ RSpec.describe 'Tags API', type: :request do
       get "/tags/name/#{ CGI.escape('spec_tag') }"
 
       expect(response).to have_http_status(:ok)
-      json = JSON.parse(response.body)
 
       expect(json).to have_key('id')
       expect(json).to have_key('name')
diff --git a/backend/spec/requests/wiki_spec.rb b/backend/spec/requests/wiki_spec.rb
index 3f2b981..cf3dc07 100644
--- a/backend/spec/requests/wiki_spec.rb
+++ b/backend/spec/requests/wiki_spec.rb
@@ -16,9 +16,8 @@ RSpec.describe 'Wiki API', type: :request do
       get '/wiki'
 
       expect(response).to have_http_status(:ok)
-      json = JSON.parse(response.body)
 
-      expect(json).to be_a(Array)
+      expect(json).to be_an(Array)
       expect(json).not_to be_empty
 
       expect(json[0]).to have_key('title')
@@ -26,12 +25,225 @@ RSpec.describe 'Wiki API', type: :request do
     end
   end
 
+  describe 'GET /wiki/:id' do
+    subject(:request) do
+      get "/wiki/#{ page_id }"
+    end
+
+    let(:page_id) { page.id }
+
+    context 'when wiki page exists' do
+      it 'returns wiki page with title' do
+        request
+        expect(response).to have_http_status(:ok)
+
+        expect(json).to include(
+            'id'        => page.id,
+            'title'     => 'spec_wiki_title')
+      end
+    end
+
+    context 'when wiki page does not exist' do
+      let(:page_id) { 9_999_999 }
+
+      it 'returns 404' do
+        request
+        expect(response).to have_http_status(:not_found)
+      end
+    end
+  end
+
+  describe 'POST /wiki' do
+    let(:endpoint) { '/wiki' }
+
+    let(:member) { create(:user, role: 'member') }
+    let(:guest) { create(:user, role: 'guest') }
+
+    def auth_headers(user)
+      { 'X-Transfer-Code' => user.inheritance_code }
+    end
+
+    context 'when not logged in' do
+      it 'returns 401' do
+        post endpoint, params: { title: 'Test', body: 'Hello' }
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when logged in but not member' do
+      it 'returns 403' do
+        post endpoint, params: { title: 'Test', body: 'Hello' }, headers: auth_headers(guest)
+        expect(response).to have_http_status(:forbidden)
+      end
+    end
+
+    context 'when params invalid' do
+      it 'returns 422 when title blank' do
+        post endpoint, params: { title: '', body: 'Hello' }, headers: auth_headers(member)
+        expect(response).to have_http_status(:unprocessable_entity)
+      end
+
+      it 'returns 422 when body blank' do
+        post endpoint, params: { title: 'Test', body: '' }, headers: auth_headers(member)
+        expect(response).to have_http_status(:unprocessable_entity)
+      end
+    end
+
+    context 'when success' do
+      it 'creates wiki_page and first content revision' do
+        expect do
+          post endpoint, params: { title: 'TestPage', body: "a\nb\nc", message: 'init' },
+                         headers: auth_headers(member)
+        end
+            .to change(WikiPage, :count).by(1)
+            .and change(WikiRevision, :count).by(1)
+
+        expect(response).to have_http_status(:created)
+
+        page_id = json.fetch('id')
+        expect(json.fetch('title')).to eq('TestPage')
+
+        page = WikiPage.find(page_id)
+        rev = page.current_revision
+        expect(rev).to be_present
+        expect(rev).to be_content
+        expect(rev.message).to eq('init')
+
+        # body が復元できること
+        expect(page.body).to eq("a\nb\nc")
+
+        # 行数とリレーションの整合
+        expect(rev.lines_count).to eq(3)
+        expect(rev.wiki_revision_lines.order(:position).pluck(:position)).to eq([0, 1, 2])
+        expect(rev.wiki_lines.pluck(:body)).to match_array(%w[a b c])
+      end
+
+      it 'reuses existing WikiLine rows by sha256' do
+        # 先に同じ行を作っておく
+        WikiLine.create!(sha256: Digest::SHA256.hexdigest('a'), body: 'a', created_at: Time.current, updated_at: Time.current)
+
+        post endpoint,
+             params: { title: 'Reuse', body: "a\na" },
+             headers: auth_headers(member)
+
+        page = WikiPage.find(JSON.parse(response.body).fetch('id'))
+        rev = page.current_revision
+        expect(rev.lines_count).to eq(2)
+
+        # "a" の WikiLine が増殖しない（1行のはず）
+        expect(WikiLine.where(body: 'a').count).to eq(1)
+      end
+    end
+  end
+
+  describe 'PUT /wiki/:id' do
+    let(:member) { create(:user, role: 'member', inheritance_code: SecureRandom.hex(16)) }
+    let(:guest)  { create(:user, role: 'guest',  inheritance_code: SecureRandom.hex(16)) }
+
+    def auth_headers(user)
+      { 'X-Transfer-Code' => user.inheritance_code }
+    end
+
+    #let!(:page) { create(:wiki_page, title: 'TestPage') }
+    let!(:page) do
+      build(:wiki_page, title: 'TestPage').tap do |p|
+        puts p.errors.full_messages unless p.valid?
+        p.save!
+      end
+    end
+
+    before do
+      # 初期版を 1 つ作っておく（更新が“2版目”になるように）
+      Wiki::Commit.content!(page: page, body: "a\nb", created_user: member, message: 'init')
+    end
+
+    context 'when not logged in' do
+      it 'returns 401' do
+        put "/wiki/#{page.id}", params: { title: 'TestPage', body: 'x' }
+        expect(response).to have_http_status(:unauthorized)
+      end
+    end
+
+    context 'when logged in but not member' do
+      it 'returns 403' do
+        put "/wiki/#{page.id}",
+            params: { title: 'TestPage', body: 'x' },
+            headers: auth_headers(guest)
+        expect(response).to have_http_status(:forbidden)
+      end
+    end
+
+    context 'when params invalid' do
+      it 'returns 422 when body blank' do
+        put "/wiki/#{page.id}",
+            params: { title: 'TestPage', body: '' },
+            headers: auth_headers(member)
+        expect(response).to have_http_status(:unprocessable_entity)
+      end
+
+      it 'returns 422 when title mismatched (if you forbid rename here)' do
+        put "/wiki/#{page.id}",
+            params: { title: 'OtherTitle', body: 'x' },
+            headers: auth_headers(member)
+        # 君の controller 例だと title 変更は 422 にしてた
+        expect(response).to have_http_status(:unprocessable_entity)
+      end
+    end
+
+    context 'when success' do
+      it 'creates new revision and returns 200' do
+        current_id = page.wiki_revisions.maximum(:id)
+
+        expect do
+          put "/wiki/#{page.id}",
+              params: { title: 'TestPage', body: "x\ny", message: 'edit', base_revision_id: current_id },
+              headers: auth_headers(member)
+        end.to change(WikiRevision, :count).by(1)
+
+        expect(response).to have_http_status(:ok)
+
+        page.reload
+        rev = page.current_revision
+        expect(rev).to be_content
+        expect(rev.message).to eq('edit')
+        expect(page.body).to eq("x\ny")
+        expect(rev.base_revision_id).to eq(current_id)
+      end
+    end
+
+    # TODO: コンフリクト未実装のため，実装したらコメント外す．
+    # context 'when conflict' do
+    #   it 'returns 409 when base_revision_id mismatches' do
+    #     # 先に別ユーザ（同じ member でもOK）が 1 回更新して先頭を進める
+    #     Wiki::Commit.content!(page: page, body: "zzz", created_user: member, message: 'other edit')
+    #     page.reload
+
+    #     stale_id = page.wiki_revisions.order(:id).first.id # わざと古い id
+    #     put "/wiki/#{page.id}",
+    #         params: { title: 'TestPage', body: 'x', base_revision_id: stale_id },
+    #         headers: auth_headers(member)
+
+    #     expect(response).to have_http_status(:conflict)
+    #     json = JSON.parse(response.body)
+    #     expect(json['error']).to eq('conflict')
+    #   end
+    # end
+
+    context 'when page not found' do
+      it 'returns 404' do
+        put "/wiki/99999999",
+            params: { title: 'X', body: 'x' },
+            headers: auth_headers(member)
+        expect(response).to have_http_status(:not_found)
+      end
+    end
+  end
+
   describe 'GET /wiki/title/:title' do
     it 'returns wiki page by title' do
       get "/wiki/title/#{CGI.escape('spec_wiki_title')}"
 
       expect(response).to have_http_status(:ok)
-      json = JSON.parse(response.body)
 
       expect(json).to have_key('id')
       expect(json).to have_key('title')