diff --git a/code/CMakeLists.txt b/code/CMakeLists.txt
index 94e0714..d409480 100644
--- a/code/CMakeLists.txt
+++ b/code/CMakeLists.txt
@@ -1,13 +1,31 @@
 cmake_minimum_required(VERSION 3.20)
-# Automatisch Projektname aus Parent-Ordner
 
 set(PROJECT_NAME "conformallab_core")
-
 project(${PROJECT_NAME} LANGUAGES C CXX)
 
 message(STATUS "Configuring ${PROJECT_NAME}...")
 
-# Build-Setup
+# ── Build modes ────────────────────────────────────────────────────────────────
+#
+#   Default (CI / tests-only): only Eigen + GTest are required.
+#
+#   -DWITH_CGAL=ON   builds the conformallab_core CLI app (needs CGAL).
+#                    Automatically enables WITH_VIEWER because the app uses
+#                    the viewer library for mesh visualisation.
+#
+#   -DWITH_VIEWER=ON builds the viewer library standalone (libigl/GLFW/GLAD).
+#
+# ──────────────────────────────────────────────────────────────────────────────
+option(WITH_CGAL   "Build conformallab_core app (requires CGAL + Viewer)" OFF)
+option(WITH_VIEWER "Build viewer library (libigl / GLFW / GLAD)"          OFF)
+
+# The CLI app always needs the viewer; enable it implicitly.
+if(WITH_CGAL AND NOT WITH_VIEWER)
+    message(STATUS "WITH_CGAL implies WITH_VIEWER – enabling automatically.")
+    set(WITH_VIEWER ON CACHE BOOL "" FORCE)
+endif()
+
+# ── Standard settings ──────────────────────────────────────────────────────────
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
@@ -18,20 +36,18 @@ if(NOT CMAKE_BUILD_TYPE)
   set(CMAKE_BUILD_TYPE "Release" CACHE STRING "Build type" FORCE)
 endif()
 
-# Compiler-Warnings & Optimierungen
 if(CMAKE_CXX_COMPILER_ID MATCHES "Clang|GNU")
   add_compile_options(-Wall -Wextra -Wpedantic)
-  
-  # AddressSanitizer nur im Debug (nicht für Tests, da gtest_discover_tests
-  # die Binary zur Buildzeit ausführt und ASan dabei hängt)
+
+  # AddressSanitizer only in Debug (gtest_discover_tests runs the binary at
+  # configure time and hangs with ASan enabled).
   if(CMAKE_BUILD_TYPE STREQUAL "Debug" AND NOT BUILD_TESTING)
     add_compile_options(-fsanitize=address -fno-omit-frame-pointer)
     add_link_options(-fsanitize=address)
   endif()
 endif()
 
-
-# ----- Testing (Google Test via FetchContent) -----
+# ── GTest (always – tests are always built) ────────────────────────────────────
 include(FetchContent)
 include(CTest)
 enable_testing()
@@ -45,38 +61,44 @@ set(gtest_force_shared_crt ON CACHE BOOL "" FORCE)
 set(INSTALL_GTEST          OFF CACHE BOOL "" FORCE)
 set(BUILD_GMOCK            OFF CACHE BOOL "" FORCE)
 FetchContent_MakeAvailable(googletest)
-# --------------------------------------------------
 
+# ── External deps (lazy tarball extraction) ────────────────────────────────────
 add_subdirectory(deps)
-add_subdirectory(deps/glfw-3.4)
 
-# --------- GLAD (global) ---------
-add_library(glad STATIC ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-glad/src/glad.c)
-target_include_directories(glad PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-glad/include)
-# --------- VIEWER Lib (separat → nur bei src/viewer/* Änderung gebaut!) ---------
-add_library(viewer STATIC src/viewer/simple_viewer.cpp)
-target_include_directories(viewer PUBLIC
-  ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-2.6.0/include
-  ${CMAKE_CURRENT_SOURCE_DIR}/include  
-  ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-glad/include
-  ${CMAKE_CURRENT_SOURCE_DIR}/deps/eigen-3.4.0/
-)  
-target_link_libraries(viewer PUBLIC glad glfw)  
-# --------- Executable ---------
-add_executable(${PROJECT_NAME} src/apps/v0/conformallab_cli.cpp)
-target_include_directories(${PROJECT_NAME} SYSTEM PRIVATE
-  ${CMAKE_CURRENT_SOURCE_DIR}/deps/single_includes
-  ${CMAKE_CURRENT_SOURCE_DIR}/deps/eigen-3.4.0/
-  ${CMAKE_CURRENT_SOURCE_DIR}/deps/CGAL-6.1.1/include
-  ${CMAKE_CURRENT_SOURCE_DIR}/deps/boost_1_90_0/
-  ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-2.6.0/include  
-)
-target_include_directories(${PROJECT_NAME} PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/include)
-#-------- Compiler-Definitionen ---------
-target_compile_definitions(${PROJECT_NAME} PRIVATE CGAL_DISABLE_GMP CGAL_DISABLE_MPFR)
-target_link_libraries(${PROJECT_NAME} PRIVATE viewer)
-#--------- Output-Ordner ---------
-set_target_properties(${PROJECT_NAME} PROPERTIES RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/bin)
+# ── Viewer library (optional) ──────────────────────────────────────────────────
+if(WITH_VIEWER)
+    add_subdirectory(deps/glfw-3.4)
 
+    add_library(glad STATIC
+        ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-glad/src/glad.c)
+    target_include_directories(glad PUBLIC
+        ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-glad/include)
+
+    add_library(viewer STATIC src/viewer/simple_viewer.cpp)
+    target_include_directories(viewer PUBLIC
+        ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-2.6.0/include
+        ${CMAKE_CURRENT_SOURCE_DIR}/include
+        ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-glad/include
+        ${CMAKE_CURRENT_SOURCE_DIR}/deps/eigen-3.4.0/)
+    target_link_libraries(viewer PUBLIC glad glfw)
+endif()
+
+# ── Core CLI app (optional, requires CGAL + Viewer) ───────────────────────────
+if(WITH_CGAL)
+    add_executable(${PROJECT_NAME} src/apps/v0/conformallab_cli.cpp)
+    target_include_directories(${PROJECT_NAME} SYSTEM PRIVATE
+        ${CMAKE_CURRENT_SOURCE_DIR}/deps/single_includes
+        ${CMAKE_CURRENT_SOURCE_DIR}/deps/eigen-3.4.0/
+        ${CMAKE_CURRENT_SOURCE_DIR}/deps/CGAL-6.1.1/include
+        ${CMAKE_CURRENT_SOURCE_DIR}/deps/libigl-2.6.0/include)
+    target_include_directories(${PROJECT_NAME} PRIVATE
+        ${CMAKE_CURRENT_SOURCE_DIR}/include)
+    target_compile_definitions(${PROJECT_NAME} PRIVATE
+        CGAL_DISABLE_GMP CGAL_DISABLE_MPFR)
+    target_link_libraries(${PROJECT_NAME} PRIVATE viewer)
+    set_target_properties(${PROJECT_NAME} PROPERTIES
+        RUNTIME_OUTPUT_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/bin)
+endif()
+
+# ── Tests (always) ────────────────────────────────────────────────────────────
 add_subdirectory(tests)
-
diff --git a/code/deps/Cmakelists.txt b/code/deps/Cmakelists.txt
index d6a0910..025c852 100644
--- a/code/deps/Cmakelists.txt
+++ b/code/deps/Cmakelists.txt
@@ -1,5 +1,16 @@
 # deps/CMakeLists.txt
-function(setup_dependency NAME  SUBDIR)
+#
+# Lazy tarball extraction – a dependency is only extracted when its directory
+# does not yet exist.  Extraction happens at cmake configure time.
+#
+# Which deps are extracted depends on the active build mode:
+#
+#   (default)      Eigen only          → tests-only build
+#   WITH_VIEWER=ON + Eigen, libigl, libigl-glad, glfw
+#   WITH_CGAL=ON   + Eigen, CGAL       (WITH_VIEWER is implied by WITH_CGAL)
+#
+
+function(setup_dependency NAME SUBDIR)
     if(NOT EXISTS "${CMAKE_CURRENT_SOURCE_DIR}/${NAME}")
         file(MAKE_DIRECTORY "${NAME}")
         file(GLOB TARBALL "${CMAKE_CURRENT_SOURCE_DIR}/tarballs/${NAME}.tar.*")
@@ -7,20 +18,21 @@ function(setup_dependency NAME  SUBDIR)
         if(NOT TARBALL)
             message(FATAL_ERROR "❌ No '${NAME}*.tar.*' in deps/tarballs/")
         else()
-            message(STATUS "${CMAKE_COMMAND}  ${TARBALL}" )
-   
+            message(STATUS "${CMAKE_COMMAND}  ${TARBALL}")
             if(SUBDIR STREQUAL "")
-                execute_process(COMMAND "${CMAKE_COMMAND}" -E tar xf "${TARBALL}"  RESULT_VARIABLE TAR_STATUS  WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}" )
-                message(STATUS "Extracting ${NAME}... Output: ${TAR_OUTPUT} Status: ${TAR_STATUS}")
-                if(NOT TAR_STATUS EQUAL 0)
-                    message(FATAL_ERROR "❌ Extract failed: ${NAME}")
-                endif()
+                execute_process(
+                    COMMAND "${CMAKE_COMMAND}" -E tar xf "${TARBALL}"
+                    RESULT_VARIABLE TAR_STATUS
+                    WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}")
             else()
-                execute_process(COMMAND "${CMAKE_COMMAND}" -E tar xf "${TARBALL}" "${NAME}/${SUBDIR}"  RESULT_VARIABLE TAR_STATUS  WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}" )
-                message(STATUS "Extracting ${NAME}... Output: ${TAR_OUTPUT} Status: ${TAR_STATUS}")
-                if(NOT TAR_STATUS EQUAL 0)
-                    message(FATAL_ERROR "❌ Extract failed: ${NAME}")
-                endif()        
+                execute_process(
+                    COMMAND "${CMAKE_COMMAND}" -E tar xf "${TARBALL}" "${NAME}/${SUBDIR}"
+                    RESULT_VARIABLE TAR_STATUS
+                    WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}")
+            endif()
+            message(STATUS "Extracting ${NAME}... Status: ${TAR_STATUS}")
+            if(NOT TAR_STATUS EQUAL 0)
+                message(FATAL_ERROR "❌ Extract failed: ${NAME}")
             endif()
         endif()
     else()
@@ -28,10 +40,17 @@ function(setup_dependency NAME  SUBDIR)
     endif()
 endfunction()
 
-setup_dependency("CGAL-6.1.1" "include" )
-setup_dependency("eigen-3.4.0" "Eigen"  )
-setup_dependency("boost_1_90_0" "boost"  )
-setup_dependency("libigl-2.6.0" "include"  )
-setup_dependency("libigl-glad" "" )
-setup_dependency("glfw-3.4" ""  )
+# ── Always required ────────────────────────────────────────────────────────────
+setup_dependency("eigen-3.4.0" "Eigen")
 
+# ── Viewer mode ────────────────────────────────────────────────────────────────
+if(WITH_VIEWER)
+    setup_dependency("libigl-2.6.0"  "include")
+    setup_dependency("libigl-glad"   "")
+    setup_dependency("glfw-3.4"      "")
+endif()
+
+# ── CGAL mode ─────────────────────────────────────────────────────────────────
+if(WITH_CGAL)
+    setup_dependency("CGAL-6.1.1" "include")
+endif()
diff --git a/code/deps/tarballs/boost_1_90_0.tar.gz b/code/deps/tarballs/boost_1_90_0.tar.gz
deleted file mode 100644
index 1e830b4..0000000
Binary files a/code/deps/tarballs/boost_1_90_0.tar.gz and /dev/null differ
diff --git a/code/src/main.cpp b/code/src/main.cpp
deleted file mode 100644
index 5c14b7a..0000000
--- a/code/src/main.cpp
+++ /dev/null
@@ -1,40 +0,0 @@
-#include <iostream>
-#include <CGAL/Simple_cartesian.h>
- 
-typedef CGAL::Simple_cartesian<double> Kernel;
-typedef Kernel::Point_2 Point_2;
-typedef Kernel::Segment_2 Segment_2;
- 
-int main()
-{
-  Point_2 p(1,1), q(10,10);
- 
-  std::cout << "p = " << p << std::endl;
-  std::cout << "q = " << q.x() << " " << q.y() << std::endl;
- 
-  std::cout << "sqdist(p,q) = "
-            << CGAL::squared_distance(p,q) << std::endl;
- 
-  Segment_2 s(p,q);
-  Point_2 m(5, 9);
- 
-  std::cout << "m = " << m << std::endl;
-  std::cout << "sqdist(Segment_2(p,q), m) = "
-            << CGAL::squared_distance(s,m) << std::endl;
- 
-  std::cout << "p, q, and m ";
-  switch (CGAL::orientation(p,q,m)){
-  case CGAL::COLLINEAR:
-    std::cout << "are collinear\n";
-    break;
-  case CGAL::LEFT_TURN:
-    std::cout << "make a left turn\n";
-    break;
-  case CGAL::RIGHT_TURN:
-    std::cout << "make a right turn\n";
-    break;
-  }
- 
-  std::cout << " midpoint(p,q) = " << CGAL::midpoint(p,q) << std::endl;
-  return 0;
-}
\ No newline at end of file