diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index d3591572..e2d96df1 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -39,10 +39,10 @@ jobs:
         run: cmake --build . -j$(nproc)
 
   # -------------------------------------------------
-  # 2. FULL BUILD + TEST + SIMPLE DAG RUN + DOCS (RelWithDebInfo + Eigen)
+  # 2. FULL BUILD + TEST + SIMPLE DAG RUN + COVERAGE + DOCS (RelWithDebInfo + Eigen)
   # -------------------------------------------------
   test_and_run:
-    name: Build & Test (RelWithDebInfo + Eigen)
+    name: Build, Test & Coverage (RelWithDebInfo + Eigen)
     runs-on: ubuntu-latest
     needs: build_matrix
     if: github.event_name == 'pull_request' || github.ref == 'refs/heads/master'
@@ -55,21 +55,42 @@ jobs:
           sudo apt-get update
           sudo apt-get install -y --no-install-recommends \
             make gcc g++ git libboost-all-dev \
-            doxygen graphviz python3-pip libeigen3-dev
+            doxygen graphviz python3-pip libeigen3-dev lcov
           pip3 install --upgrade pip
           pip3 install cmake==3.21.3
 
       - name: Configure
-        run: cmake -S . -B build -DCMAKE_BUILD_TYPE=RelWithDebInfo -DBUILD_TESTS=ON
+        run: cmake -S . -B build -DCMAKE_BUILD_TYPE=RelWithDebInfo -DBUILD_TESTS=ON -DENABLE_COVERAGE=ON
 
       - name: Build all targets
         working-directory: ${{ github.workspace }}/build
         run: cmake --build . -j$(nproc)
 
-      - name: Run tests
+      - name: Run tests with coverage
         working-directory: ${{ github.workspace }}/build
-        run: ctest --output-on-failure --output-junit test_results.xml
-        continue-on-error: true
+        run: |
+          # Run tests
+          ctest --output-on-failure --output-junit test_results.xml
+
+          # Capture coverage ONLY from include/
+          lcov --capture --directory . \
+               --output-file coverage.info \
+               --ignore-errors empty,mismatch \
+               --include '*/OneStopParallel/include/*'
+
+          # Remove unused warnings + ignore tests/apps
+          lcov --remove coverage.info '*/tests/*' '*/apps/*' \
+               --ignore-errors unused,empty,mismatch \
+               --output-file coverage.info
+
+          # Generate HTML report
+          genhtml coverage.info --output-directory coverage_html
+
+      - name: Upload coverage artifacts
+        uses: actions/upload-artifact@v4
+        with:
+          name: coverage-report
+          path: build/coverage_html
 
       - name: Upload test results
         uses: actions/upload-artifact@v4
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 84c5327a..bb0e0ae0 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -25,6 +25,15 @@ set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF) # Ensure C++17 standard is strictly enforced
 
+# --- Code Coverage (optional) ---
+option(ENABLE_COVERAGE "Enable code coverage flags" OFF)
+
+if(ENABLE_COVERAGE AND CMAKE_CXX_COMPILER_ID MATCHES "GNU|Clang")
+    message(STATUS "Code coverage enabled")
+    add_compile_options(--coverage -g)
+    add_link_options(--coverage)
+endif()
+
 # Configure git hooks
 add_subdirectory(.githooks)
 
@@ -102,7 +111,7 @@ target_compile_options(ProjectExecutableFlags INTERFACE
         # Else (not Debug)
         $<IF:$<CONFIG:RelWithDebInfo>,
             # RelWithDebInfo flags
-            -O3;-g,
+            -O3;-g;-DNDEBUG,
             # Release and other/custom flags
             -O3;-DNDEBUG
         >