diff --git a/include/forfun/best_time_to_buy_and_sell_stock.hpp b/include/forfun/best_time_to_buy_and_sell_stock.hpp
index e0e66e3..8e13125 100644
--- a/include/forfun/best_time_to_buy_and_sell_stock.hpp
+++ b/include/forfun/best_time_to_buy_and_sell_stock.hpp
@@ -24,7 +24,7 @@ calc_max_profit(Iter iter, Sentinel const last) noexcept
 {
     using TypeValue = std::iter_value_t<Iter>;
 
-    if (iter == last)
+    if (iter == last) [[unlikely]]
     {
         return TypeValue{0};
     }
@@ -59,7 +59,7 @@ calc_max_profit(Iter iter, Sentinel const last) noexcept
 {
     using TypeValue = std::iter_value_t<Iter>;
 
-    if (iter == last)
+    if (iter == last) [[unlikely]]
     {
         return TypeValue{0};
     }
@@ -96,7 +96,7 @@ calc_max_profit(Iter iter, Sentinel const last) noexcept
 {
     using TypeValue = std::iter_value_t<Iter>;
 
-    if (iter == last)
+    if (iter == last) [[unlikely]]
     {
         return TypeValue{0};
     }
diff --git a/include/forfun/evaluate_reverse_polish_notation.hpp b/include/forfun/evaluate_reverse_polish_notation.hpp
index fba72e2..353ff80 100644
--- a/include/forfun/evaluate_reverse_polish_notation.hpp
+++ b/include/forfun/evaluate_reverse_polish_notation.hpp
@@ -27,7 +27,7 @@ template <std::contiguous_iterator Iter, std::sentinel_for<Iter> Sentinel>
 [[nodiscard]] auto eval_expression(Iter iter, Sentinel const end)
     -> std::pair<int, std::errc>
 {
-    if (iter == end)
+    if (iter == end) [[unlikely]]
     {
         return {0, std::errc{}};
     }
@@ -76,7 +76,7 @@ template <std::contiguous_iterator Iter, std::sentinel_for<Iter> Sentinel>
                 accumulator *= operand_2;
                 break;
             case '/':
-                if (operand_2 == 0)
+                if (operand_2 == 0) [[unlikely]]
                 {
                     // NOLINTNEXTLINE(cppcoreguidelines-avoid-goto,hicpp-avoid-goto)
                     goto invalid_argument;
@@ -109,7 +109,7 @@ template <std::contiguous_iterator Iter, std::sentinel_for<Iter> Sentinel>
 [[nodiscard]] auto eval_expression(Iter iter, Sentinel const end)
     -> std::pair<int, std::errc>
 {
-    if (iter == end)
+    if (iter == end) [[unlikely]]
     {
         return {0, std::errc{}};
     }
diff --git a/include/forfun/factorial.hpp b/include/forfun/factorial.hpp
index 2bed12c..9b4a66c 100644
--- a/include/forfun/factorial.hpp
+++ b/include/forfun/factorial.hpp
@@ -51,7 +51,7 @@ template <common::concepts::addition_unpromoted T>
 {
     assert(n >= T{0});
 
-    if (n <= T{1})
+    if (n <= T{1}) [[unlikely]]
     {
         return T{1};
     }
diff --git a/include/forfun/fibonacci.hpp b/include/forfun/fibonacci.hpp
index 8eefe55..cc5a628 100644
--- a/include/forfun/fibonacci.hpp
+++ b/include/forfun/fibonacci.hpp
@@ -38,9 +38,9 @@ namespace recursive {
 template <common::concepts::addition_unpromoted T>
 [[nodiscard]] constexpr auto fib(T const n) noexcept -> T
 {
-    if (n <= T{2})
+    if (n <= T{2}) [[unlikely]]
     {
-        if (n < T{1})
+        if (n < T{1}) [[unlikely]]
         {
             return T{0};
         }
diff --git a/include/forfun/fizzbuzz.hpp b/include/forfun/fizzbuzz.hpp
index 01fefd2..ee29ee2 100644
--- a/include/forfun/fizzbuzz.hpp
+++ b/include/forfun/fizzbuzz.hpp
@@ -68,7 +68,7 @@ fizzbuzz(int start, int const last, BinaryFunc write) noexcept(noexcept(write))
         {
             write(buzz.data(), buzz.size());
         }
-        else if (is_numeric)
+        else if (is_numeric) [[likely]]
         {
             // Create char buffer sufficient for int's maximum number of decimal
             // digits and one sign.
diff --git a/include/forfun/gcd.hpp b/include/forfun/gcd.hpp
index fd3b82b..6387fa6 100644
--- a/include/forfun/gcd.hpp
+++ b/include/forfun/gcd.hpp
@@ -18,7 +18,7 @@ namespace detail {
 
 [[nodiscard]] constexpr auto gcd_imp(int const m, int const n) noexcept -> int
 {
-    if (n == 0)
+    if (n == 0) [[unlikely]]
     {
         return m;
     }
diff --git a/include/forfun/last_stone_weight.hpp b/include/forfun/last_stone_weight.hpp
index 9b05e02..796f6b4 100644
--- a/include/forfun/last_stone_weight.hpp
+++ b/include/forfun/last_stone_weight.hpp
@@ -30,7 +30,7 @@ last_stone_weight(Iter const first, Sentinel last) noexcept
 {
     using ValueType = std::iter_value_t<Iter>;
 
-    if (first == last)
+    if (first == last) [[unlikely]]
     {
         return ValueType{0};
     }
@@ -136,7 +136,7 @@ template <std::contiguous_iterator Iter, std::sentinel_for<Iter> Sentinel>
 last_stone_weight(Iter const first, Sentinel last) noexcept
     -> std::iter_value_t<Iter>
 {
-    if (first == last)
+    if (first == last) [[unlikely]]
     {
         return 0;
     }
diff --git a/include/forfun/maximum_subarray.hpp b/include/forfun/maximum_subarray.hpp
index d55a19a..3784f30 100644
--- a/include/forfun/maximum_subarray.hpp
+++ b/include/forfun/maximum_subarray.hpp
@@ -31,7 +31,7 @@ max_sum(Iter const first, Sentinel const end) noexcept
 {
     using T = PromotedValueType<std::iter_value_t<Iter>>;
 
-    if (first == end)
+    if (first == end) [[unlikely]]
     {
         return T{0};
     }
@@ -67,7 +67,7 @@ template <std::forward_iterator Iter, std::sentinel_for<Iter> Sentinel>
     PromotedValueType<std::iter_value_t<Iter>> sum
 ) noexcept -> PromotedValueType<std::iter_value_t<Iter>>
 {
-    if (iter == end)
+    if (iter == end) [[unlikely]]
     {
         return sum;
     }
@@ -87,7 +87,7 @@ template <std::forward_iterator Iter, std::sentinel_for<Iter> Sentinel>
 {
     using T = PromotedValueType<std::iter_value_t<Iter>>;
 
-    if (iter == end)
+    if (iter == end) [[unlikely]]
     {
         return T{0};
     }
@@ -106,7 +106,7 @@ template <std::forward_iterator Iter, std::sentinel_for<Iter> Sentinel>
 {
     using T = PromotedValueType<std::iter_value_t<Iter>>;
 
-    if (iter == last)
+    if (iter == last) [[unlikely]]
     {
         return T{0};
     }
diff --git a/include/forfun/move_zeroes.hpp b/include/forfun/move_zeroes.hpp
index fe0b830..843a4b4 100644
--- a/include/forfun/move_zeroes.hpp
+++ b/include/forfun/move_zeroes.hpp
@@ -27,7 +27,7 @@ constexpr auto move_zeroes(Itr itr, Sentinel const end) noexcept -> void
     auto itr_j{itr};
     for (; itr != end; ++itr)
     {
-        if (*itr != ValType{0})
+        if (*itr != ValType{0}) [[likely]]
         {
             std::iter_swap(itr, itr_j);
             ++itr_j;
@@ -48,7 +48,7 @@ constexpr auto move_zeroes(Itr itr, Sentinel const end) noexcept -> void
     auto itr_j{itr};
     for (; itr != end; ++itr)
     {
-        if (*itr != ValType{0})
+        if (*itr != ValType{0}) [[likely]]
         {
             *itr_j = *itr;
             ++itr_j;
@@ -74,7 +74,7 @@ constexpr auto move_zeroes(Itr itr, Sentinel const end) noexcept -> void
     auto itr_j{itr};
     for (; itr != end; ++itr)
     {
-        if (*itr != ValType{0})
+        if (*itr != ValType{0}) [[likely]]
         {
             *itr_j = *itr;
             ++itr_j;
diff --git a/include/forfun/primality.hpp b/include/forfun/primality.hpp
index 4cb9f7f..ee60709 100644
--- a/include/forfun/primality.hpp
+++ b/include/forfun/primality.hpp
@@ -20,12 +20,12 @@ template <std::unsigned_integral UInteger>
 is_prime(UInteger const n) noexcept(noexcept(std::sqrt(std::declval<UInteger>())
 )) -> bool
 {
-    if (n < UInteger{2U})
+    if (n < UInteger{2U}) [[unlikely]]
     {
         return false;
     }
 
-    if (n == UInteger{2U})
+    if (n == UInteger{2U}) [[unlikely]]
     {
         return true;
     }
diff --git a/include/forfun/product_except_self.hpp b/include/forfun/product_except_self.hpp
index d0fde77..fa92959 100644
--- a/include/forfun/product_except_self.hpp
+++ b/include/forfun/product_except_self.hpp
@@ -100,7 +100,7 @@ constexpr auto product_except_self(
     using ValType = std::iter_value_t<OutItr>;
     using DiffType = std::iter_difference_t<InItr>;
 
-    if (first == last)
+    if (first == last) [[unlikely]]
     {
         return;
     }
diff --git a/include/forfun/sorting/bubble_sort.hpp b/include/forfun/sorting/bubble_sort.hpp
index 128f0d5..d506f9f 100644
--- a/include/forfun/sorting/bubble_sort.hpp
+++ b/include/forfun/sorting/bubble_sort.hpp
@@ -21,7 +21,7 @@ template <std::contiguous_iterator Iter, std::sized_sentinel_for<Iter> Sentinel>
     requires std::sortable<Iter>
 constexpr auto bubble_sort(Iter const begin, Sentinel end) noexcept -> void
 {
-    if (begin == end)
+    if (begin == end) [[unlikely]]
     {
         return;
     }
@@ -58,7 +58,7 @@ constexpr auto bubble_sort(Iter const begin, Sentinel end) noexcept -> void
 {
     using DiffType = std::iter_difference_t<Iter>;
 
-    if (begin == end)
+    if (begin == end) [[unlikely]]
     {
         return;
     }
diff --git a/include/forfun/sorting/insertion_sort.hpp b/include/forfun/sorting/insertion_sort.hpp
index 3da476d..52a0965 100644
--- a/include/forfun/sorting/insertion_sort.hpp
+++ b/include/forfun/sorting/insertion_sort.hpp
@@ -22,7 +22,7 @@ constexpr auto insertion_sort(Iter const begin, Sentinel const end) noexcept
 {
     using DiffType = std::iter_difference_t<Iter>;
 
-    if (begin != end)
+    if (begin != end) [[likely]]
     {
         for (Iter it_i{begin + DiffType{1}}; it_i != end; ++it_i)
         {
diff --git a/include/forfun/sub_array_sums.hpp b/include/forfun/sub_array_sums.hpp
index 582cbfb..b373c66 100644
--- a/include/forfun/sub_array_sums.hpp
+++ b/include/forfun/sub_array_sums.hpp
@@ -39,7 +39,7 @@ constexpr auto sum_each(
 
     auto const sums_size{sums.size()};
 
-    if (sums_size == SizeType{0U})
+    if (sums_size == SizeType{0U}) [[unlikely]]
     {
         return;
     }
diff --git a/include/forfun/top_k_frequent_elements.hpp b/include/forfun/top_k_frequent_elements.hpp
index 9cccb03..993a0a2 100644
--- a/include/forfun/top_k_frequent_elements.hpp
+++ b/include/forfun/top_k_frequent_elements.hpp
@@ -37,7 +37,7 @@ top_frequent(Iter const first, Sentinel const end, std::size_t k)
 {
     using ValType = std::iter_value_t<Iter>;
 
-    if (first == end)
+    if (first == end) [[unlikely]]
     {
         return {};
     }
@@ -107,7 +107,7 @@ top_frequent(Iter const first, Sentinel const end, std::size_t k)
 {
     using ValType = std::iter_value_t<Iter>;
 
-    if (first == end)
+    if (first == end) [[unlikely]]
     {
         return {};
     }
diff --git a/include/forfun/tower_of_hanoi.hpp b/include/forfun/tower_of_hanoi.hpp
index d363c3c..0b3f114 100644
--- a/include/forfun/tower_of_hanoi.hpp
+++ b/include/forfun/tower_of_hanoi.hpp
@@ -19,7 +19,7 @@ constexpr auto
 toh(Rod& src, Rod& des, Rod& aux, Monk monk, std::integral auto num_moves
 ) noexcept(noexcept(monk(src, des))) -> void
 {
-    if (num_moves == decltype(num_moves){0})
+    if (num_moves == decltype(num_moves){0}) [[unlikely]]
     {
         return;
     }
diff --git a/include/forfun/trie.hpp b/include/forfun/trie.hpp
index 83dc501..1ebf9dd 100644
--- a/include/forfun/trie.hpp
+++ b/include/forfun/trie.hpp
@@ -53,7 +53,7 @@ auto insert(T& root, StringViewT<T> const& word) -> void
     using LenT = StringViewT<T>::size_type;
 
     auto const word_len{word.length()};
-    if (word_len == LenT{0U})
+    if (word_len == LenT{0U}) [[unlikely]]
     {
         return;
     }
diff --git a/src/forfun/container/list.cpp b/src/forfun/container/list.cpp
index 1773b11..c8b0e3a 100644
--- a/src/forfun/container/list.cpp
+++ b/src/forfun/container/list.cpp
@@ -41,7 +41,7 @@ auto list::push_back(list::value_type value) noexcept(false) -> void
         new internal::list_node(value, tail_, end_)
     };
 
-    if (head_ == end_)
+    if (head_ == end_) [[unlikely]]
     {
         head_ = n;
     }
@@ -56,7 +56,7 @@ auto list::push_back(list::value_type value) noexcept(false) -> void
 
 auto list::pop_back() noexcept -> void
 {
-    if (tail_ == end_)
+    if (tail_ == end_) [[unlikely]]
     {
         assert(head_ == end_);
         assert(size_ == size_type{});
@@ -67,7 +67,7 @@ auto list::pop_back() noexcept -> void
     assert(size_ > size_type{});
     assert(head_ != end_);
 
-    if (tail_->previous_ == end_)
+    if (tail_->previous_ == end_) [[unlikely]]
     {
         assert(size_ == size_type{1});
         assert(head_ == tail_);
diff --git a/src/forfun/graph/balanced_binary_tree.cpp b/src/forfun/graph/balanced_binary_tree.cpp
index 67aea6b..4a38dc4 100644
--- a/src/forfun/graph/balanced_binary_tree.cpp
+++ b/src/forfun/graph/balanced_binary_tree.cpp
@@ -19,7 +19,7 @@ namespace {
 auto is_unbalanced_internal(binary_tree_node const* const head) noexcept
     -> std::pair<std::size_t, bool>
 {
-    if (head == nullptr)
+    if (head == nullptr) [[unlikely]]
     {
         return {std::size_t{0U}, false};
     }
@@ -68,7 +68,7 @@ namespace {
 
 auto measure_depth_internal(binary_tree_node const* const head) noexcept -> int
 {
-    if (head == nullptr)
+    if (head == nullptr) [[unlikely]]
     {
         return 0;
     }
@@ -112,7 +112,7 @@ namespace {
 auto measure_depth_internal(binary_tree_node const* const head) noexcept
     -> std::size_t
 {
-    if (head == nullptr)
+    if (head == nullptr) [[unlikely]]
     {
         return std::size_t{0U};
     }
@@ -130,7 +130,7 @@ auto measure_depth_internal(binary_tree_node const* const head) noexcept
 [[nodiscard]] auto is_balanced(binary_tree_node const* const head) noexcept
     -> bool
 {
-    if (head == nullptr)
+    if (head == nullptr) [[unlikely]]
     {
         return true;
     }
diff --git a/src/forfun/graph/subsets.cpp b/src/forfun/graph/subsets.cpp
index c3abd5f..6b12a90 100644
--- a/src/forfun/graph/subsets.cpp
+++ b/src/forfun/graph/subsets.cpp
@@ -24,7 +24,7 @@ auto do_explode_subsets(
     Container& subsets
 ) -> void
 {
-    if (iter == last)
+    if (iter == last) [[unlikely]]
     {
         subsets.emplace_back(subset);
         return;
diff --git a/src/forfun/set_matrix_zeroes.cpp b/src/forfun/set_matrix_zeroes.cpp
index a4183df..79892ba 100644
--- a/src/forfun/set_matrix_zeroes.cpp
+++ b/src/forfun/set_matrix_zeroes.cpp
@@ -17,7 +17,7 @@ auto set_zeroes(std::vector<std::vector<int>>& matrix) -> void
 {
     using DiffC = std::vector<std::vector<int>>::value_type::difference_type;
 
-    if ((matrix.begin() == matrix.end()) || matrix.front().empty())
+    if ((matrix.begin() == matrix.end()) || matrix.front().empty()) [[unlikely]]
     {
         return;
     }
@@ -98,6 +98,7 @@ auto set_zeroes(std::vector<std::vector<int>>& matrix) noexcept -> void
     using DiffC = std::vector<std::vector<int>>::value_type::difference_type;
 
     if ((matrix.begin() == matrix.end()) || matrix.begin()->empty())
+        [[unlikely]]
     {
         return;
     }
@@ -175,14 +176,14 @@ auto set_zeroes(std::vector<std::vector<int>>& matrix) noexcept -> void
 
     auto const matrix_r_size{matrix.size()};
 
-    if (matrix_r_size == SizeTypeR{0U})
+    if (matrix_r_size == SizeTypeR{0U}) [[unlikely]]
     {
         return;
     }
 
     auto const matrix_c_size{matrix.begin()->size()};
 
-    if (matrix_c_size == SizeTypeC{0U})
+    if (matrix_c_size == SizeTypeC{0U}) [[unlikely]]
     {
         return;
     }
diff --git a/src/forfun/sonar.cpp b/src/forfun/sonar.cpp
index cc39288..aa19850 100644
--- a/src/forfun/sonar.cpp
+++ b/src/forfun/sonar.cpp
@@ -22,7 +22,7 @@ namespace forfun::sonar {
     int const width{std::abs(area.right - area.left)};
     int const height{std::abs(area.bottom - area.top)};
 
-    if ((width + height) == 0)
+    if ((width + height) == 0) [[unlikely]]
     {
         return 1;
     }
diff --git a/src/forfun/valid_anagram.cpp b/src/forfun/valid_anagram.cpp
index c0e21a5..05c684c 100644
--- a/src/forfun/valid_anagram.cpp
+++ b/src/forfun/valid_anagram.cpp
@@ -19,7 +19,7 @@ namespace forfun::valid_anagram::char_only {
 {
     using Iter = std::string_view::const_iterator;
 
-    if (s.length() != t.length())
+    if (s.length() != t.length()) [[unlikely]]
     {
         return false;
     }