diff --git a/CHANGELOG.md b/CHANGELOG.md
index a2b6d00..45912b7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -29,3 +29,10 @@ All notable changes to cargoxx will be documented in this file.
   Dependencies are emitted alphabetically (matches Cargo). Round-trip
   property is exercised by `tests/manifest_write.cpp` (9 cases).
   Defaulted `operator==` on the manifest structs supports comparison.
+- `cargoxx.layout` public types (`Target`, `TargetKind`, `DiscoveredLayout`)
+  and `discover(project_root, package_name)`. Walks `src/` recursively
+  for the library (excluding the `src/bin/` subtree), enumerates
+  `src/main.cpp`, `src/bin/*.cpp`, `tests/*.cpp`, `examples/*.cpp` flat,
+  sorts results for deterministic output, and returns `LayoutNoTarget`
+  when neither a library nor any binary is present.
+  `tests/layout_discovery.cpp` covers 12 cases.
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2e726c9..5bdf777 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -37,6 +37,7 @@ target_sources(cargoxx
         src/util/error.cpp
         src/manifest/parser.cpp
         src/manifest/writer.cpp
+        src/layout/layout.cpp
     PUBLIC
         FILE_SET CXX_MODULES FILES
             src/lib.cppm
diff --git a/src/layout/layout.cpp b/src/layout/layout.cpp
new file mode 100644
index 0000000..a31e019
--- /dev/null
+++ b/src/layout/layout.cpp
@@ -0,0 +1,142 @@
+module cargoxx.layout;
+
+import std;
+import cargoxx.util;
+
+namespace cargoxx::layout {
+
+namespace {
+
+namespace fs = std::filesystem;
+
+auto top_level_cpp(const fs::path& dir) -> std::vector<fs::path> {
+    std::vector<fs::path> out;
+    std::error_code ec;
+    if (!fs::exists(dir, ec) || ec) {
+        return out;
+    }
+    for (const auto& entry : fs::directory_iterator{dir}) {
+        if (entry.is_regular_file() && entry.path().extension() == ".cpp") {
+            out.push_back(entry.path());
+        }
+    }
+    std::ranges::sort(out);
+    return out;
+}
+
+void walk_library_sources(const fs::path& src_dir, const fs::path& lib_path,
+                          const fs::path& main_path, std::vector<fs::path>& cppm_out,
+                          std::vector<fs::path>& cpp_out) {
+    std::error_code ec;
+    if (!fs::exists(src_dir, ec) || ec) {
+        return;
+    }
+    for (const auto& entry : fs::recursive_directory_iterator{src_dir}) {
+        if (!entry.is_regular_file()) {
+            continue;
+        }
+        const auto& p = entry.path();
+        // Exclude the bin/ subtree — it holds extra binary roots, not library sources.
+        auto rel = fs::relative(p, src_dir);
+        if (!rel.empty() && rel.begin()->string() == "bin") {
+            continue;
+        }
+        if (p == lib_path || p == main_path) {
+            continue;
+        }
+        const auto ext = p.extension();
+        if (ext == ".cppm") {
+            cppm_out.push_back(p);
+        } else if (ext == ".cpp") {
+            cpp_out.push_back(p);
+        }
+    }
+}
+
+auto by_name(const Target& a, const Target& b) -> bool {
+    return a.name < b.name;
+}
+
+} // namespace
+
+auto discover(const fs::path& project_root, const std::string& package_name)
+    -> util::Result<DiscoveredLayout> {
+    const auto src_dir = project_root / "src";
+    const auto lib_path = src_dir / "lib.cppm";
+    const auto main_path = src_dir / "main.cpp";
+    const auto bin_dir = src_dir / "bin";
+    const auto tests_dir = project_root / "tests";
+    const auto examples_dir = project_root / "examples";
+
+    DiscoveredLayout out;
+
+    std::error_code ec;
+    if (fs::exists(lib_path, ec) && !ec) {
+        std::vector<fs::path> cppm{lib_path};
+        std::vector<fs::path> cpp;
+        walk_library_sources(src_dir, lib_path, main_path, cppm, cpp);
+        std::ranges::sort(cppm);
+        std::ranges::sort(cpp);
+        out.library = Target{
+            .kind = TargetKind::Library,
+            .name = package_name,
+            .entry = lib_path,
+            .additional_sources = std::move(cpp),
+            .module_units = std::move(cppm),
+        };
+    }
+
+    if (fs::exists(main_path, ec) && !ec) {
+        out.binaries.push_back(Target{
+            .kind = TargetKind::Binary,
+            .name = package_name,
+            .entry = main_path,
+            .additional_sources = {},
+            .module_units = {},
+        });
+    }
+    for (const auto& f : top_level_cpp(bin_dir)) {
+        out.binaries.push_back(Target{
+            .kind = TargetKind::Binary,
+            .name = f.stem().string(),
+            .entry = f,
+            .additional_sources = {},
+            .module_units = {},
+        });
+    }
+    std::ranges::sort(out.binaries, by_name);
+
+    for (const auto& f : top_level_cpp(tests_dir)) {
+        out.tests.push_back(Target{
+            .kind = TargetKind::Test,
+            .name = f.stem().string(),
+            .entry = f,
+            .additional_sources = {},
+            .module_units = {},
+        });
+    }
+
+    for (const auto& f : top_level_cpp(examples_dir)) {
+        out.examples.push_back(Target{
+            .kind = TargetKind::Example,
+            .name = f.stem().string(),
+            .entry = f,
+            .additional_sources = {},
+            .module_units = {},
+        });
+    }
+
+    if (!out.library && out.binaries.empty()) {
+        return std::unexpected(util::Error{
+            util::ErrorCode::LayoutNoTarget,
+            "no target found",
+            "expected one of: src/main.cpp, src/lib.cppm",
+            project_root,
+            std::nullopt,
+        });
+    }
+
+    return out;
+}
+
+} // namespace cargoxx::layout
diff --git a/src/layout/layout.cppm b/src/layout/layout.cppm
index 49ab611..83ab3e9 100644
--- a/src/layout/layout.cppm
+++ b/src/layout/layout.cppm
@@ -1,3 +1,32 @@
 export module cargoxx.layout;
 
+import std;
 import cargoxx.util;
+
+export namespace cargoxx::layout {
+
+enum class TargetKind { Library, Binary, Test, Example };
+
+struct Target {
+    TargetKind kind;
+    std::string name;
+    std::filesystem::path entry;
+    std::vector<std::filesystem::path> additional_sources;
+    std::vector<std::filesystem::path> module_units;
+
+    bool operator==(const Target&) const = default;
+};
+
+struct DiscoveredLayout {
+    std::optional<Target> library;
+    std::vector<Target> binaries;
+    std::vector<Target> tests;
+    std::vector<Target> examples;
+
+    bool operator==(const DiscoveredLayout&) const = default;
+};
+
+auto discover(const std::filesystem::path& project_root, const std::string& package_name)
+    -> util::Result<DiscoveredLayout>;
+
+} // namespace cargoxx::layout
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index b26d29d..8b3c9d2 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -10,3 +10,4 @@ endfunction()
 cargoxx_add_test(util_error)
 cargoxx_add_test(manifest_parse)
 cargoxx_add_test(manifest_write)
+cargoxx_add_test(layout_discovery)
diff --git a/tests/layout_discovery.cpp b/tests/layout_discovery.cpp
new file mode 100644
index 0000000..e3dc4c2
--- /dev/null
+++ b/tests/layout_discovery.cpp
@@ -0,0 +1,193 @@
+#include <catch2/catch_test_macros.hpp>
+
+import cargoxx.layout;
+import cargoxx.util;
+import std;
+
+using cargoxx::layout::DiscoveredLayout;
+using cargoxx::layout::discover;
+using cargoxx::layout::Target;
+using cargoxx::layout::TargetKind;
+using cargoxx::util::ErrorCode;
+
+namespace {
+
+class TempProject {
+  public:
+    TempProject() {
+        root_ = std::filesystem::temp_directory_path() /
+                std::format("cargoxx-layout-test-{}", std::random_device{}());
+        std::filesystem::create_directories(root_);
+    }
+
+    ~TempProject() {
+        std::error_code ec;
+        std::filesystem::remove_all(root_, ec);
+    }
+
+    TempProject(const TempProject&) = delete;
+    TempProject& operator=(const TempProject&) = delete;
+    TempProject(TempProject&&) = delete;
+    TempProject& operator=(TempProject&&) = delete;
+
+    auto root() const -> const std::filesystem::path& { return root_; }
+
+    auto touch(std::string_view rel) -> std::filesystem::path {
+        auto p = root_ / rel;
+        std::filesystem::create_directories(p.parent_path());
+        std::ofstream{p} << "// stub\n";
+        return p;
+    }
+
+  private:
+    std::filesystem::path root_;
+};
+
+} // namespace
+
+TEST_CASE("discover returns LayoutNoTarget for an empty src", "[layout]") {
+    TempProject p;
+    std::filesystem::create_directories(p.root() / "src");
+    auto r = discover(p.root(), "foo");
+    REQUIRE_FALSE(r.has_value());
+    REQUIRE(r.error().code == ErrorCode::LayoutNoTarget);
+}
+
+TEST_CASE("discover finds main.cpp as a binary", "[layout]") {
+    TempProject p;
+    auto main = p.touch("src/main.cpp");
+    auto r = discover(p.root(), "foo");
+    REQUIRE(r.has_value());
+    REQUIRE_FALSE(r->library.has_value());
+    REQUIRE(r->binaries.size() == 1);
+    REQUIRE(r->binaries[0].kind == TargetKind::Binary);
+    REQUIRE(r->binaries[0].name == "foo");
+    REQUIRE(r->binaries[0].entry == main);
+}
+
+TEST_CASE("discover finds lib.cppm as a library", "[layout]") {
+    TempProject p;
+    auto lib = p.touch("src/lib.cppm");
+    auto r = discover(p.root(), "foo");
+    REQUIRE(r.has_value());
+    REQUIRE(r->library.has_value());
+    REQUIRE(r->library->kind == TargetKind::Library);
+    REQUIRE(r->library->name == "foo");
+    REQUIRE(r->library->entry == lib);
+    REQUIRE(r->library->module_units == std::vector{lib});
+    REQUIRE(r->library->additional_sources.empty());
+    REQUIRE(r->binaries.empty());
+}
+
+TEST_CASE("discover supports lib + main together", "[layout]") {
+    TempProject p;
+    p.touch("src/lib.cppm");
+    p.touch("src/main.cpp");
+    auto r = discover(p.root(), "foo");
+    REQUIRE(r.has_value());
+    REQUIRE(r->library.has_value());
+    REQUIRE(r->binaries.size() == 1);
+    REQUIRE(r->binaries[0].entry.filename() == "main.cpp");
+}
+
+TEST_CASE("discover collects nested .cppm and .cpp into the library",
+          "[layout]") {
+    TempProject p;
+    auto lib = p.touch("src/lib.cppm");
+    auto inner_cppm = p.touch("src/internal/foo.cppm");
+    auto inner_cpp = p.touch("src/internal/foo.cpp");
+    auto r = discover(p.root(), "foo");
+    REQUIRE(r.has_value());
+    REQUIRE(r->library->module_units.size() == 2);
+    REQUIRE(std::ranges::find(r->library->module_units, lib) !=
+            r->library->module_units.end());
+    REQUIRE(std::ranges::find(r->library->module_units, inner_cppm) !=
+            r->library->module_units.end());
+    REQUIRE(r->library->additional_sources == std::vector{inner_cpp});
+}
+
+TEST_CASE("discover excludes src/bin/* from the library walk", "[layout]") {
+    TempProject p;
+    p.touch("src/lib.cppm");
+    p.touch("src/bin/tool.cpp");
+    auto r = discover(p.root(), "foo");
+    REQUIRE(r.has_value());
+    REQUIRE(r->library->additional_sources.empty());
+    REQUIRE(r->binaries.size() == 1);
+    REQUIRE(r->binaries[0].name == "tool");
+}
+
+TEST_CASE("discover lists src/bin/*.cpp as additional binaries", "[layout]") {
+    TempProject p;
+    p.touch("src/main.cpp");
+    p.touch("src/bin/foo.cpp");
+    p.touch("src/bin/bar.cpp");
+    auto r = discover(p.root(), "pkg");
+    REQUIRE(r.has_value());
+    REQUIRE(r->binaries.size() == 3);
+    // sorted alphabetically by target name
+    REQUIRE(r->binaries[0].name == "bar");
+    REQUIRE(r->binaries[1].name == "foo");
+    REQUIRE(r->binaries[2].name == "pkg");
+}
+
+TEST_CASE("discover does not recurse into src/bin/", "[layout]") {
+    TempProject p;
+    p.touch("src/main.cpp");
+    p.touch("src/bin/foo.cpp");
+    p.touch("src/bin/sub/nested.cpp"); // should be ignored
+    auto r = discover(p.root(), "pkg");
+    REQUIRE(r.has_value());
+    REQUIRE(r->binaries.size() == 2);
+}
+
+TEST_CASE("discover lists tests/*.cpp", "[layout]") {
+    TempProject p;
+    p.touch("src/main.cpp");
+    p.touch("tests/alpha.cpp");
+    p.touch("tests/beta.cpp");
+    p.touch("tests/sub/nested.cpp"); // ignored, no recursion
+    auto r = discover(p.root(), "pkg");
+    REQUIRE(r.has_value());
+    REQUIRE(r->tests.size() == 2);
+    REQUIRE(r->tests[0].name == "alpha");
+    REQUIRE(r->tests[0].kind == TargetKind::Test);
+    REQUIRE(r->tests[1].name == "beta");
+}
+
+TEST_CASE("discover lists examples/*.cpp", "[layout]") {
+    TempProject p;
+    p.touch("src/main.cpp");
+    p.touch("examples/demo.cpp");
+    auto r = discover(p.root(), "pkg");
+    REQUIRE(r.has_value());
+    REQUIRE(r->examples.size() == 1);
+    REQUIRE(r->examples[0].name == "demo");
+    REQUIRE(r->examples[0].kind == TargetKind::Example);
+}
+
+TEST_CASE("discover ignores non .cpp/.cppm files", "[layout]") {
+    TempProject p;
+    p.touch("src/main.cpp");
+    p.touch("src/notes.txt");
+    p.touch("src/lib.cppm");
+    p.touch("src/internal/header.h"); // headers in src/ are ignored
+    auto r = discover(p.root(), "pkg");
+    REQUIRE(r.has_value());
+    REQUIRE(r->library->module_units.size() == 1);
+    REQUIRE(r->library->additional_sources.empty());
+}
+
+TEST_CASE("discover output is deterministic across runs", "[layout]") {
+    TempProject p;
+    p.touch("src/lib.cppm");
+    p.touch("src/zeta.cppm");
+    p.touch("src/alpha.cppm");
+    p.touch("src/middle.cppm");
+    auto r1 = discover(p.root(), "pkg");
+    auto r2 = discover(p.root(), "pkg");
+    REQUIRE(r1.has_value());
+    REQUIRE(r2.has_value());
+    REQUIRE(*r1 == *r2);
+    REQUIRE(std::ranges::is_sorted(r1->library->module_units));
+}