diff --git a/CHANGELOG.md b/CHANGELOG.md
index 06be61d6..28bc4138 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,13 @@
 
 ### Added
 - new debugger commands: `stack <n>` and `locals <n>` to print the values on the stack and in the current locals scope
+- custom format specifiers for lists:
+  - `:n` to remove surrounding brackets,
+  - `:c` / `:nc` to use `, ` as a separator instead of ` `,
+  - `:l` / `:nl` to use `\n` as a separator,
+  - `:?s` to format as an escaped quoted string,
+  - `:s` to format as a quoted string
+- `format` can use format specifiers for integers: `b`, `#b`, `B`, `#B`, `c`, `d`, `o`, `x`, `#x`, `X`, and `#X` if the argument is an integer
 
 ### Changed
 
diff --git a/src/arkreactor/Builtins/String.cpp b/src/arkreactor/Builtins/String.cpp
index e74edbf8..16a880bd 100644
--- a/src/arkreactor/Builtins/String.cpp
+++ b/src/arkreactor/Builtins/String.cpp
@@ -1,20 +1,190 @@
 #include <Ark/Builtins/Builtins.hpp>
 
 #include <utility>
+#include <cmath>
 #include <utf8.hpp>
 #include <fmt/args.h>
+#include <fmt/base.h>
+#include <fmt/ostream.h>
 #include <fmt/core.h>
+#include <fmt/ranges.h>
 #include <fmt/format.h>
 
 #include <Ark/TypeChecker.hpp>
 #include <Ark/VM/VM.hpp>
 
+struct value_wrapper
+{
+    const Ark::Value& value;
+    Ark::VM* vm_ptr;
+    bool nested = false;
+};
+
+template <>
+struct fmt::formatter<value_wrapper>
+{
+private:
+    fmt::basic_string_view<char> opening_bracket_ = fmt::detail::string_literal<char, '['> {};
+    fmt::basic_string_view<char> closing_bracket_ = fmt::detail::string_literal<char, ']'> {};
+    fmt::basic_string_view<char> separator_ = fmt::detail::string_literal<char, ' '> {};
+    bool is_debug = false;
+    bool is_literal_str = false;
+    fmt::formatter<std::string> underlying_;
+
+public:
+    void set_brackets(const fmt::basic_string_view<char> open, const fmt::basic_string_view<char> close)
+    {
+        opening_bracket_ = open;
+        closing_bracket_ = close;
+    }
+
+    void set_separator(const fmt::basic_string_view<char> sep)
+    {
+        separator_ = sep;
+    }
+
+    format_parse_context::iterator parse(fmt::format_parse_context& ctx)
+    {
+        auto it = ctx.begin();
+        const auto end = ctx.end();
+        if (it == end)
+            return underlying_.parse(ctx);
+
+        switch (detail::to_ascii(*it))
+        {
+            case 'n':
+                set_brackets({}, {});
+                ++it;
+                if (it == end)
+                    report_error("invalid format specifier");
+                if (*it == '}')
+                    return it;
+                if (*it != 'c' && *it != 'l')
+                    report_error("invalid format specifier. Expected either :nc or :nl");
+                [[fallthrough]];
+
+            case 'c':
+                if (*it == 'c')
+                {
+                    set_separator(fmt::detail::string_literal<char, ',', ' '> {});
+                    ++it;
+                    return it;
+                }
+                [[fallthrough]];
+
+            case 'l':
+                set_separator(fmt::detail::string_literal<char, '\n'> {});
+                ++it;
+                return it;
+
+            case '?':
+                is_debug = true;
+                set_brackets({}, {});
+                ++it;
+                if (it == end || *it != 's')
+                    report_error("invalid format specifier. Expected :?s, not :?");
+                [[fallthrough]];
+
+            case 's':
+                if (!is_debug)
+                {
+                    set_brackets(fmt::detail::string_literal<char, '"'> {},
+                                 fmt::detail::string_literal<char, '"'> {});
+                    set_separator({});
+                    is_literal_str = true;
+                }
+                ++it;
+                return it;
+
+            default:
+                break;
+        }
+
+        if (it != end && *it != '}')
+        {
+            if (*it != ':')
+                report_error("invalid format specifier");
+            ++it;
+        }
+
+        ctx.advance_to(it);
+        return underlying_.parse(ctx);
+    }
+
+    template <typename Output, typename It, typename Sentinel>
+    auto write_debug_string(Output& out, It it, Sentinel end, Ark::VM* vm_ptr) const -> Output
+    {
+        auto buf = fmt::basic_memory_buffer<char>();
+        for (; it != end; ++it)
+        {
+            auto formatted = it->toString(*vm_ptr);
+            buf.append(formatted);
+        }
+        auto specs = fmt::format_specs();
+        specs.set_type(fmt::presentation_type::debug);
+        return fmt::detail::write<char>(
+            out,
+            fmt::basic_string_view<char>(buf.data(), buf.size()),
+            specs);
+    }
+
+    fmt::format_context::iterator format(const value_wrapper& value, fmt::format_context& ctx) const
+    {
+        auto out = ctx.out();
+        auto it = fmt::detail::range_begin(value.value.constList());
+        const auto end = fmt::detail::range_end(value.value.constList());
+        if (is_debug)
+            return write_debug_string(out, it, end, value.vm_ptr);
+
+        if ((is_literal_str && !value.nested) || !is_literal_str)
+            out = fmt::detail::copy<char>(opening_bracket_, out);
+
+        for (int i = 0; it != end; ++it)
+        {
+            if (i > 0)
+                out = fmt::detail::copy<char>(separator_, out);
+            ctx.advance_to(out);
+
+            auto&& item = *it;
+            if (item.valueType() == Ark::ValueType::List)
+            {
+                // if :s, do not put surrounding "" here
+                format({ item, value.vm_ptr, /* nested= */ true }, ctx);
+            }
+            else
+            {
+                std::string formatted = item.toString(*value.vm_ptr);
+                out = underlying_.format(formatted, ctx);
+            }
+
+            ++i;
+        }
+
+        if ((is_literal_str && !value.nested) || !is_literal_str)
+            out = detail::copy<char>(closing_bracket_, out);
+
+        return out;
+    }
+};
+
 namespace Ark::internal::Builtins::String
 {
     /**
      * @name format
      * @brief Format a String given replacements
-     * @details https://fmt.dev/12.0/syntax/
+     * @details See [fmt.dev](https://fmt.dev/12.0/syntax/) for syntax.
+     * =details-begin
+     * In the case of lists, we have custom specifiers:
+     * - `n` removes surrounding brackets, uses ' ' as a separator
+     * - `?s` debug format. The list is formatted as an escaped string
+     * - `s` string format. The list is formatted as a string
+     * - `c` changes the separator to ', '
+     * - `l` changes the separator to '\n'
+     *
+     * `n` can be combined with either `c` and `l` (which are mutually exclusive): `nc`, `nl`.
+     *
+     * The underlying formatter is the one of strings, so you can write `::<10` to align all elements left in a 10 char wide block each.
+     * =details-end
      * @param format the String to format
      * @param values as any argument as you need, of any valid ArkScript type
      * =begin
@@ -42,13 +212,30 @@ namespace Ark::internal::Builtins::String
             if (it->valueType() == ValueType::String)
                 store.push_back(it->stringRef());
             else if (it->valueType() == ValueType::Number)
-                store.push_back(it->number());
+            {
+                double int_part;
+                if (std::modf(it->number(), &int_part) == 0.0)
+                    store.push_back(static_cast<long>(it->number()));
+                else
+                    store.push_back(it->number());
+            }
             else if (it->valueType() == ValueType::Nil)
                 store.push_back("nil");
             else if (it->valueType() == ValueType::True)
                 store.push_back("true");
             else if (it->valueType() == ValueType::False)
                 store.push_back("false");
+            else if (it->valueType() == ValueType::List)
+            {
+                // std::vector<value_wrapper> r;
+                // std::ranges::transform(
+                //     it->list(),
+                //     std::back_inserter(r),
+                //     [&vm](const Value& val) -> value_wrapper {
+                //         return value_wrapper { val, vm };
+                //     });
+                store.push_back(value_wrapper { *it, vm });
+            }
             else
                 store.push_back(it->toString(*vm));
         }
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_b.ark b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_b.ark
new file mode 100644
index 00000000..19b33aef
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_b.ark
@@ -0,0 +1 @@
+(print (format "{:b}" 65.1))
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_b.expected b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_b.expected
new file mode 100644
index 00000000..d85c2781
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_b.expected
@@ -0,0 +1,6 @@
+format: can not format "{:b}" (1 argument provided) because of invalid format specifier
+
+In file tests/unittests/resources/DiagnosticsSuite/runtime/format_double_b.ark:1
+    1 | (print (format "{:b}" 65.1))
+      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~
+    2 |
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_c.ark b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_c.ark
new file mode 100644
index 00000000..2362133d
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_c.ark
@@ -0,0 +1 @@
+(print (format "{:c}" 65.1))
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_c.expected b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_c.expected
new file mode 100644
index 00000000..34d9a8b5
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_c.expected
@@ -0,0 +1,6 @@
+format: can not format "{:c}" (1 argument provided) because of invalid format specifier
+
+In file tests/unittests/resources/DiagnosticsSuite/runtime/format_double_c.ark:1
+    1 | (print (format "{:c}" 65.1))
+      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~
+    2 |
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_d.ark b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_d.ark
new file mode 100644
index 00000000..0088033c
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_d.ark
@@ -0,0 +1 @@
+(print (format "{:d}" 65.1))
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_d.expected b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_d.expected
new file mode 100644
index 00000000..0d68383f
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_d.expected
@@ -0,0 +1,6 @@
+format: can not format "{:d}" (1 argument provided) because of invalid format specifier
+
+In file tests/unittests/resources/DiagnosticsSuite/runtime/format_double_d.ark:1
+    1 | (print (format "{:d}" 65.1))
+      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~
+    2 |
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_b.ark b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_b.ark
new file mode 100644
index 00000000..4a724ccb
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_b.ark
@@ -0,0 +1 @@
+(print (format "{:#b}" 65.1))
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_b.expected b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_b.expected
new file mode 100644
index 00000000..0d4ebb9f
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_b.expected
@@ -0,0 +1,6 @@
+format: can not format "{:#b}" (1 argument provided) because of invalid format specifier
+
+In file tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_b.ark:1
+    1 | (print (format "{:#b}" 65.1))
+      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    2 |
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_upper_b.ark b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_upper_b.ark
new file mode 100644
index 00000000..8f6c207a
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_upper_b.ark
@@ -0,0 +1 @@
+(print (format "{:#B}" 65.1))
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_upper_b.expected b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_upper_b.expected
new file mode 100644
index 00000000..7c65ac03
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_upper_b.expected
@@ -0,0 +1,6 @@
+format: can not format "{:#B}" (1 argument provided) because of invalid format specifier
+
+In file tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_upper_b.ark:1
+    1 | (print (format "{:#B}" 65.1))
+      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    2 |
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_upper_x.ark b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_upper_x.ark
new file mode 100644
index 00000000..91fab277
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_upper_x.ark
@@ -0,0 +1 @@
+(print (format "{:#X}" 65.1))
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_upper_x.expected b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_upper_x.expected
new file mode 100644
index 00000000..2526be08
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_upper_x.expected
@@ -0,0 +1,6 @@
+format: can not format "{:#X}" (1 argument provided) because of invalid format specifier
+
+In file tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_upper_x.ark:1
+    1 | (print (format "{:#X}" 65.1))
+      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    2 |
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_x.ark b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_x.ark
new file mode 100644
index 00000000..181daa42
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_x.ark
@@ -0,0 +1 @@
+(print (format "{:#x}" 65.1))
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_x.expected b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_x.expected
new file mode 100644
index 00000000..8522f33e
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_x.expected
@@ -0,0 +1,6 @@
+format: can not format "{:#x}" (1 argument provided) because of invalid format specifier
+
+In file tests/unittests/resources/DiagnosticsSuite/runtime/format_double_hashtag_x.ark:1
+    1 | (print (format "{:#x}" 65.1))
+      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
+    2 |
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_o.ark b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_o.ark
new file mode 100644
index 00000000..63bad4e9
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_o.ark
@@ -0,0 +1 @@
+(print (format "{:o}" 65.1))
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_o.expected b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_o.expected
new file mode 100644
index 00000000..7e41bc17
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_o.expected
@@ -0,0 +1,6 @@
+format: can not format "{:o}" (1 argument provided) because of invalid format specifier
+
+In file tests/unittests/resources/DiagnosticsSuite/runtime/format_double_o.ark:1
+    1 | (print (format "{:o}" 65.1))
+      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~
+    2 |
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_upper_b.ark b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_upper_b.ark
new file mode 100644
index 00000000..bfd062d1
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_upper_b.ark
@@ -0,0 +1 @@
+(print (format "{:B}" 65.1))
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_upper_b.expected b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_upper_b.expected
new file mode 100644
index 00000000..c83556e9
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_upper_b.expected
@@ -0,0 +1,6 @@
+format: can not format "{:B}" (1 argument provided) because of invalid format specifier
+
+In file tests/unittests/resources/DiagnosticsSuite/runtime/format_double_upper_b.ark:1
+    1 | (print (format "{:B}" 65.1))
+      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~
+    2 |
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_upper_x.ark b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_upper_x.ark
new file mode 100644
index 00000000..cd8ba91b
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_upper_x.ark
@@ -0,0 +1 @@
+(print (format "{:X}" 65.1))
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_upper_x.expected b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_upper_x.expected
new file mode 100644
index 00000000..f24ae27f
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_upper_x.expected
@@ -0,0 +1,6 @@
+format: can not format "{:X}" (1 argument provided) because of invalid format specifier
+
+In file tests/unittests/resources/DiagnosticsSuite/runtime/format_double_upper_x.ark:1
+    1 | (print (format "{:X}" 65.1))
+      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~
+    2 |
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_x.ark b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_x.ark
new file mode 100644
index 00000000..0d491473
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_x.ark
@@ -0,0 +1 @@
+(print (format "{:x}" 65.1))
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_x.expected b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_x.expected
new file mode 100644
index 00000000..135b33a6
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_double_x.expected
@@ -0,0 +1,6 @@
+format: can not format "{:x}" (1 argument provided) because of invalid format specifier
+
+In file tests/unittests/resources/DiagnosticsSuite/runtime/format_double_x.ark:1
+    1 | (print (format "{:x}" 65.1))
+      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~
+    2 |
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid.ark b/tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid.ark
new file mode 100644
index 00000000..845bd71b
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid.ark
@@ -0,0 +1 @@
+(print (format "{:d}" []))
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid.expected b/tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid.expected
new file mode 100644
index 00000000..8fefe45d
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid.expected
@@ -0,0 +1,6 @@
+format: can not format "{:d}" (1 argument provided) because of invalid format specifier
+
+In file tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid.ark:1
+    1 | (print (format "{:d}" []))
+      | ^~~~~~~~~~~~~~~~~~~~~~~~~
+    2 |
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid_debug.ark b/tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid_debug.ark
new file mode 100644
index 00000000..f51cc17a
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid_debug.ark
@@ -0,0 +1 @@
+(print (format "{:?}" []))
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid_debug.expected b/tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid_debug.expected
new file mode 100644
index 00000000..496a6919
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid_debug.expected
@@ -0,0 +1,6 @@
+format: can not format "{:?}" (1 argument provided) because of invalid format specifier. Expected :?s, not :?
+
+In file tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid_debug.ark:1
+    1 | (print (format "{:?}" []))
+      | ^~~~~~~~~~~~~~~~~~~~~~~~~
+    2 |
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid_na.ark b/tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid_na.ark
new file mode 100644
index 00000000..f86ffd2f
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid_na.ark
@@ -0,0 +1 @@
+(print (format "{:na}" []))
diff --git a/tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid_na.expected b/tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid_na.expected
new file mode 100644
index 00000000..e19daa93
--- /dev/null
+++ b/tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid_na.expected
@@ -0,0 +1,6 @@
+format: can not format "{:na}" (1 argument provided) because of invalid format specifier. Expected either :nc or :nl
+
+In file tests/unittests/resources/DiagnosticsSuite/runtime/format_list_invalid_na.ark:1
+    1 | (print (format "{:na}" []))
+      | ^~~~~~~~~~~~~~~~~~~~~~~~~~
+    2 |
diff --git a/tests/unittests/resources/LangSuite/string-tests.ark b/tests/unittests/resources/LangSuite/string-tests.ark
index d297f247..5c87b4ae 100644
--- a/tests/unittests/resources/LangSuite/string-tests.ark
+++ b/tests/unittests/resources/LangSuite/string-tests.ark
@@ -58,4 +58,27 @@
 
     (test:case "format strings" {
         (test:eq "nilfalsetrue" (format "{}{}{}" nil false true))
-        (test:eq "CProcedure" (format "{}" print)) })})
+        (test:eq "CProcedure" (format "{}" print))
+
+        (test:eq (format "{}"     ["hel\tlo" 1 nil [true "a" 2]]) "[hel	lo 1 nil [true a 2]]")
+        (test:eq (format "{::}"   ["hel\tlo" 1 nil [true "a" 2]]) "[hel	lo 1 nil [true a 2]]")
+        (test:eq (format "{:n}"   ["hel\tlo" 1 nil [true "a" 2]]) "hel	lo 1 nil true a 2")
+        (test:eq (format "{:?s}"  ["hel\tlo" 1 nil [true "a" 2]]) "\"hel\\tlo1nil[true \\\"a\\\" 2]\"")
+        (test:eq (format "{:s}"   ["hel\tlo" 1 nil [true "a" 2]]) "\"hel	lo1niltruea2\"")
+        (test:eq (format "{:c}"   ["hel\tlo" 1 nil [true "a" 2]]) "[hel	lo, 1, nil, [true, a, 2]]")
+        (test:eq (format "{:l}"   ["hel\tlo" 1 nil [true "a" 2]]) "[hel	lo\n1\nnil\n[true\na\n2]]")
+        (test:eq (format "{:nc}"  ["hel\tlo" 1 nil [true "a" 2]]) "hel	lo, 1, nil, true, a, 2")
+        (test:eq (format "{:nl}"  ["hel\tlo" 1 nil [true "a" 2]]) "hel	lo\n1\nnil\ntrue\na\n2")
+        (test:eq (format "{::<5}" ["hello" 1 nil [true "a" 2]])   "[hello 1     nil   [true  a     2    ]]")
+
+        (test:eq (format "{:b}"  65) "1000001")
+        (test:eq (format "{:#b}" 65) "0b1000001")
+        (test:eq (format "{:B}"  65) "1000001")
+        (test:eq (format "{:#B}" 65) "0B1000001")
+        (test:eq (format "{:c}"  65) "A")
+        (test:eq (format "{:d}"  65) "65")
+        (test:eq (format "{:o}"  65) "101")
+        (test:eq (format "{:x}"  63) "3f")
+        (test:eq (format "{:#x}" 63) "0x3f")
+        (test:eq (format "{:X}"  63) "3F")
+        (test:eq (format "{:#X}" 63) "0X3F") })})