diff --git a/CMakeLists.txt b/CMakeLists.txt
index 4f82ad95..9d568c41 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -435,6 +435,7 @@ if (TESTS)
 
     list (
         APPEND TEST_BIN
+        ascii
         algo/sort
         alloc/aligned
         alloc/arena
diff --git a/ascii.hpp b/ascii.hpp
index 9dca4e09..5f13b77f 100644
--- a/ascii.hpp
+++ b/ascii.hpp
@@ -51,6 +51,42 @@ namespace util::ascii {
     }
 
 
+    //-------------------------------------------------------------------------
+    constexpr inline
+    bool
+    is_lower (char c) noexcept
+    {
+        return c >= 'a' && c <= 'z';
+    }
+
+
+    //-------------------------------------------------------------------------
+    constexpr inline
+    bool
+    is_hex (const char c) noexcept
+    {
+        switch (c) {
+        case '0'...'9': return true;
+        case 'a'...'f': return true;
+        case 'A'...'F': return true;
+        }
+
+        return false;
+    }
+
+
+    //-------------------------------------------------------------------------
+    constexpr inline
+    unsigned
+    from_hex (char c)
+    {
+        return c >= '0' && c <= '9' ? (c - '0'     ) :
+               c >= 'a' && c <= 'f' ? (c - 'a' + 10) :
+               c >= 'A' && c <= 'F' ? (c - 'A' + 10) :
+               throw std::invalid_argument ("character is not hexademical");
+    }
+
+
     ///////////////////////////////////////////////////////////////////////////
     constexpr inline
     char
diff --git a/test/ascii.cpp b/test/ascii.cpp
new file mode 100644
index 00000000..6c17d64c
--- /dev/null
+++ b/test/ascii.cpp
@@ -0,0 +1,79 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * Copyright 2017 Danny Robson <danny@nerdcruft.net>
+ */
+
+#include "tap.hpp"
+
+#include "ascii.hpp"
+
+int
+main (int, char**)
+{
+    util::TAP::logger tap;
+
+    static constexpr bool T = true;
+    static constexpr bool F = false;
+
+    static constexpr struct {
+        char character;
+
+        bool is_digit;
+        bool is_hex;
+        bool is_upper;
+        bool is_lower;
+        bool is_space;
+
+        int integer;
+        unsigned hexadecimal;
+
+        const char *msg;
+    } TESTS[] = {
+        {  '/', F, F, F, F, F, 0,  0, "/" }, // one below '0'
+        {  '0', T, T, F, F, F, 0,  0, "0" },
+        {  '9', T, T, F, F, F, 9,  9, "9" },
+        {  ':', F, F, F, F, F, 0,  0, ":" }, // one above '9'
+        {  '`', F, F, F, F, F, 0,  0, "`" }, // one below 'a'
+        {  'a', F, T, F, T, F, 0, 10, "a" },
+        {  'f', F, T, F, T, F, 0, 15, "f" },
+        {  'g', F, F, F, T, F, 0,  0, "g" },
+        {  'A', F, T, T, F, F, 0, 10, "A" },
+        {  'F', F, T, T, F, F, 0, 15, "F" },
+        {  'G', F, F, T, F, F, 0,  0, "G" },
+
+        {  ' ', F, F, F, F, T, 0,  0, "space" },
+        { '\t', F, F, F, F, T, 0,  0, "tab" },
+        { '\n', F, F, F, F, T, 0,  0, "newline" },
+    };
+
+#define TRY_BOOL(X) [&] () -> bool { try { return X; } catch (...) { return false; }; } ()
+
+    for (auto &t: TESTS) {
+        bool is_digit = TRY_BOOL(util::ascii::is_digit (t.character)) == t.is_digit;
+        bool is_hex   = TRY_BOOL(util::ascii::is_hex   (t.character)) == t.is_hex;
+        bool is_upper = TRY_BOOL(util::ascii::is_upper (t.character)) == t.is_upper;
+        bool is_lower = TRY_BOOL(util::ascii::is_lower (t.character)) == t.is_lower;
+        bool is_space = TRY_BOOL(util::ascii::is_space (t.character)) == t.is_space;
+
+        bool integer     = !t.is_digit || util::ascii::to_integer (t.character) == t.integer;
+        bool hexadecimal = !t.is_hex   || util::ascii::from_hex   (t.character) == t.hexadecimal;
+
+        tap.expect (
+            is_digit && is_hex && is_upper && is_lower && is_space && integer && hexadecimal,
+            "%s", t.msg
+        );
+    }
+
+    return tap.status ();
+}