diff --git a/DevTools/HackStudio/CMakeLists.txt b/DevTools/HackStudio/CMakeLists.txt
index 2f392cabffa..2199e1b28cf 100644
--- a/DevTools/HackStudio/CMakeLists.txt
+++ b/DevTools/HackStudio/CMakeLists.txt
@@ -1,5 +1,6 @@
 set(SOURCES
     CursorTool.cpp
+    Git/DiffViewer.cpp
     Git/GitWidget.cpp
     Git/GitFilesModel.cpp
     Git/GitRepo.cpp
@@ -29,4 +30,4 @@ set(SOURCES
 )
 
 serenity_bin(HackStudio)
-target_link_libraries(HackStudio LibWeb LibMarkdown LibGUI LibGfx LibCore LibVT LibDebug LibX86)
+target_link_libraries(HackStudio LibWeb LibMarkdown LibGUI LibGfx LibCore LibVT LibDebug LibX86 LibDiff)
diff --git a/DevTools/HackStudio/Git/GitWidget.cpp b/DevTools/HackStudio/Git/GitWidget.cpp
index e8dfb3b4a48..448ec755e9e 100644
--- a/DevTools/HackStudio/Git/GitWidget.cpp
+++ b/DevTools/HackStudio/Git/GitWidget.cpp
@@ -27,6 +27,8 @@
 #include "GitWidget.h"
 #include "GitFilesModel.h"
 #include <AK/LogStream.h>
+#include <LibCore/File.h>
+#include <LibDiff/Format.h>
 #include <LibGUI/Application.h>
 #include <LibGUI/BoxLayout.h>
 #include <LibGUI/Button.h>
@@ -36,6 +38,7 @@
 #include <LibGUI/Model.h>
 #include <LibGUI/Painter.h>
 #include <LibGfx/Bitmap.h>
+#include <stdio.h>
 
 namespace HackStudio {
 
@@ -64,6 +67,10 @@ GitWidget::GitWidget(const LexicalPath& repo_root)
     m_unstaged_files = unstaged.add<GitFilesView>(
         [this](const auto& file) { stage_file(file); },
         Gfx::Bitmap::load_from_file("/res/icons/16x16/plus.png").release_nonnull());
+    m_unstaged_files->on_selection = [this](const GUI::ModelIndex& index) {
+        const auto& selected = index.data().as_string();
+        show_diff(LexicalPath(selected));
+    };
 
     auto& staged = add<GUI::Widget>();
     staged.set_layout<GUI::VerticalBoxLayout>();
@@ -135,4 +142,29 @@ void GitWidget::commit()
     m_git_repo->commit(message);
     refresh();
 }
+
+void GitWidget::set_view_diff_callback(ViewDiffCallback callback)
+{
+    m_view_diff_callback = move(callback);
+}
+
+void GitWidget::show_diff(const LexicalPath& file_path)
+{
+    if (!m_git_repo->is_tracked(file_path)) {
+        auto file = Core::File::construct(file_path.string());
+        if (!file->open(Core::IODevice::ReadOnly)) {
+            perror("open");
+            ASSERT_NOT_REACHED();
+        }
+
+        auto content = file->read_all();
+        String content_string((char*)content.data(), content.size());
+        m_view_diff_callback("", Diff::generate_only_additions(content_string));
+        return;
+    }
+    const auto& original_content = m_git_repo->original_file_content(file_path);
+    const auto& diff = m_git_repo->unstaged_diff(file_path);
+    ASSERT(original_content.has_value() && diff.has_value());
+    m_view_diff_callback(original_content.value(), diff.value());
+}
 }
diff --git a/DevTools/HackStudio/Git/GitWidget.h b/DevTools/HackStudio/Git/GitWidget.h
index 417af9ebbba..6cc8ae8bbd7 100644
--- a/DevTools/HackStudio/Git/GitWidget.h
+++ b/DevTools/HackStudio/Git/GitWidget.h
@@ -28,17 +28,21 @@
 
 #include "GitFilesView.h"
 #include "GitRepo.h"
+#include <AK/Function.h>
 #include <LibGUI/Forward.h>
 #include <LibGUI/Widget.h>
 
 namespace HackStudio {
 
+typedef Function<void(const String& original_content, const String& diff)> ViewDiffCallback;
+
 class GitWidget final : public GUI::Widget {
     C_OBJECT(GitWidget)
 public:
     virtual ~GitWidget() override {}
 
     void refresh();
+    void set_view_diff_callback(ViewDiffCallback callback);
 
 private:
     explicit GitWidget(const LexicalPath& repo_root);
@@ -46,11 +50,13 @@ private:
     void stage_file(const LexicalPath&);
     void unstage_file(const LexicalPath&);
     void commit();
+    void show_diff(const LexicalPath&);
 
     LexicalPath m_repo_root;
     RefPtr<GitFilesView> m_unstaged_files;
     RefPtr<GitFilesView> m_staged_files;
     RefPtr<GitRepo> m_git_repo;
+    ViewDiffCallback m_view_diff_callback;
 };
 
 }
diff --git a/DevTools/HackStudio/main.cpp b/DevTools/HackStudio/main.cpp
index 045b058127b..0866c69c9f7 100644
--- a/DevTools/HackStudio/main.cpp
+++ b/DevTools/HackStudio/main.cpp
@@ -33,6 +33,7 @@
 #include "FindInFilesWidget.h"
 #include "FormEditorWidget.h"
 #include "FormWidget.h"
+#include "Git/DiffViewer.h"
 #include "Git/GitWidget.h"
 #include "HackStudio.h"
 #include "Locator.h"
@@ -99,6 +100,7 @@ RefPtr<GUI::StackWidget> g_right_hand_stack;
 RefPtr<GUI::Splitter> g_editors_splitter;
 RefPtr<GUI::Widget> g_form_inner_container;
 RefPtr<FormEditorWidget> g_form_editor_widget;
+RefPtr<DiffViewer> g_diff_viewer;
 
 static RefPtr<GUI::TabWidget> s_action_tab_widget;
 
@@ -118,6 +120,7 @@ static void add_new_editor(GUI::Widget& parent)
 enum class EditMode {
     Text,
     Form,
+    Diff,
 };
 
 static void set_edit_mode(EditMode mode)
@@ -126,7 +129,12 @@ static void set_edit_mode(EditMode mode)
         g_right_hand_stack->set_active_widget(g_editors_splitter);
     } else if (mode == EditMode::Form) {
         g_right_hand_stack->set_active_widget(g_form_inner_container);
+    } else if (mode == EditMode::Diff) {
+        g_right_hand_stack->set_active_widget(g_diff_viewer);
+    } else {
+        ASSERT_NOT_REACHED();
     }
+    g_right_hand_stack->active_widget()->update();
 }
 
 static void build(TerminalWrapper&);
@@ -416,6 +424,8 @@ static int main_impl(int argc, char** argv)
     add_properties_pane("Form widget tree:", form_widget_tree_view);
     add_properties_pane("Widget properties:", GUI::TableView::construct());
 
+    g_diff_viewer = g_right_hand_stack->add<DiffViewer>();
+
     g_editors_splitter = g_right_hand_stack->add<GUI::VerticalSplitter>();
     g_editors_splitter->layout()->set_margins({ 0, 3, 0, 0 });
     add_new_editor(*g_editors_splitter);
@@ -563,7 +573,10 @@ static int main_impl(int argc, char** argv)
     auto& debug_info_widget = s_action_tab_widget->add_tab<DebugInfoWidget>("Debug");
     auto& disassembly_widget = s_action_tab_widget->add_tab<DisassemblyWidget>("Disassembly");
     auto& git_widget = s_action_tab_widget->add_tab<GitWidget>("Git", LexicalPath(g_project->root_directory()));
-    (void)git_widget;
+    git_widget.set_view_diff_callback([](const auto& original_content, const auto& diff) {
+        g_diff_viewer->set_content(original_content, diff);
+        set_edit_mode(EditMode::Diff);
+    });
 
     auto& locator = widget.add<Locator>();