diff --git a/src/cligen.cr b/src/cligen.cr
index 398414a..b4cfc98 100644
--- a/src/cligen.cr
+++ b/src/cligen.cr
@@ -1,3 +1,4 @@
+require "./cligen/exceptions"
 require "./cligen/coercable"
 require "./cligen/parsable"
 require "./cligen/annotations"
diff --git a/src/cligen/app.cr b/src/cligen/app.cr
index 8a52bec..554b753 100644
--- a/src/cligen/app.cr
+++ b/src/cligen/app.cr
@@ -18,10 +18,25 @@ module CliGen
       super
     end
 
+    def self.handle_command_raises(&block) : Nil
+      begin
+        block.call
+      rescue e : CliGen::RuntimeError
+        abort e.message
+      rescue e : CliGen::ConfigurationError 
+        abort e.message
+      rescue e : CliGen::HelpRequestedError
+        puts e.message
+        exit 0
+      end
+    end
+
     # Convenience entry point; defaults to ARGV
     def self.process(args : Array(String) = ARGV.to_a) : Nil
       generate if @@instance.nil?
-      @@instance.not_nil!.process(args)
+      handle_command_raises do
+        @@instance.not_nil!.process(args)
+      end
     end
   end
 end
diff --git a/src/cligen/arg.cr b/src/cligen/arg.cr
index 70f2e42..e5f52c7 100644
--- a/src/cligen/arg.cr
+++ b/src/cligen/arg.cr
@@ -24,36 +24,60 @@ module CliGen
     def initialize(@value, @index)
     end
 
-    def flag? : Bool
-      if @value =~ CliGen::Regex::FLAG_REGEX
+    def self.flag?(val : String) : Bool
+      if val =~ CliGen::Regex::FLAG_REGEX
         true
       else
         false
       end
     end
 
-    def int? : Bool
-      if @value =~ /^[[:digit:]]+$/
+    def flag?(val : String = @value) : Bool
+      Arg.flag?(val)
+    end
+
+    def self.int?(val : String) : Bool
+      if val =~ CliGen::Regex::INT
         true
       else
         false
       end
     end
 
-    def float? : Bool
-      if @value =~ /^[[:digit:]]+(\.[[:digit:]]+)?$/
+    def int?(val : String = @value) : Bool
+      Arg.int?(val)
+    end
+
+    def self.uint?(val : String) : Bool
+      if val =~ CliGen::Regex::UINT
         true
       else
         false
       end
     end
 
+    def uint?(val : String = @value) : Bool
+      Arg.uint?(val)
+    end
+
+    def self.float?(val : String) : Bool
+      if val =~ CliGen::Regex::FLOAT
+        true
+      else
+        false
+      end
+    end
+
+    def float?(val : String = @value) : Bool
+      Arg.float?(val)
+    end
+
     # This serves as a trigger that tells the object that it has been processed
     # 
     # This will raise an exception if it is re-called after already having been
     # processed.
     def processed
-      raise "ERROR : CliGen::Arg(index: #{@index}, value: #{@value})#processed : This arg was re-processed" if @processed
+      raise CliGen::ArgReprocessedError.new("CliGen::Arg(index: #{@index}, value: #{@value})#processed : This arg was re-processed") if @processed
       @processed = true
     end
   end
diff --git a/src/cligen/command/argument.cr b/src/cligen/command/argument.cr
index c374712..71b4500 100644
--- a/src/cligen/command/argument.cr
+++ b/src/cligen/command/argument.cr
@@ -70,7 +70,7 @@ module CliGen
       {% if def_setter %}
       def {{variable.var}}= (value : {{type}})
         {% unless validation.nil? %}
-          raise "ERROR : #{@type.name}##{@def.name} : Provided value #{value} is not passing validation" unless {{validation}}.call(value)
+          raise CliGen::ValidationError.new("#{@type.name}##{@def.name} : Provided value #{value} failed validation") unless {{validation}}.call(value)
         {% end %}
         @{{name}} = value
       end
diff --git a/src/cligen/command/define_command_initializer.cr b/src/cligen/command/define_command_initializer.cr
index 87f7d43..6dd86d6 100644
--- a/src/cligen/command/define_command_initializer.cr
+++ b/src/cligen/command/define_command_initializer.cr
@@ -11,7 +11,7 @@ module CliGen
                 flg.validate!
                 @{{var.id}} = flg.as(CliGen::Flag({{var.type}})).value!
               else
-                raise "ERROR : {{@type.name}}\#{{@def.name}} : No flag found for \"{{var.name}}\"?"
+                raise CliGen::FlagNotFoundError.new("{{@type.name}}\#{{@def.name}} : No flag found for \"{{var.name}}\"")
               end
             {% else %}
               {% raise "ERROR : #{@type.name}#{@def.name} : Instance Variable(#{var.name}) is not handled by CliGen and does not have a default value" unless var.default_value %}
diff --git a/src/cligen/command_node.cr b/src/cligen/command_node.cr
index 4bcd8fd..d752dcc 100644
--- a/src/cligen/command_node.cr
+++ b/src/cligen/command_node.cr
@@ -63,7 +63,7 @@ module CliGen
           message += "\nShort:\n%s" % short_duplicates.map { |f| "- #{f}" }.join("\n")
         end
 
-        raise error_buffer % [@name, message]
+        raise CliGen::DuplicateFlagError.new(error_buffer % [@name, message])
       end
     end
 
@@ -75,6 +75,14 @@ module CliGen
       @flags.find{|f| f.short == short}
     end
 
+    def handle_flag_raises(&work) 
+      begin 
+        work.call
+      rescue e : CliGen::RuntimeError
+        abort e.message
+      end
+    end
+
     def find_match(arg : String)
       if subcommand?(arg)
         return CliGen::MatchType::SubCommand
@@ -172,7 +180,7 @@ module CliGen
       check_for_duplicates!(@flags)
       @commands.each(&.check!)
       {% unless T == Nil %}
-      raise "ERROR : CommandNode({{T}})#check! : {{T}} has no subcommands and no #main defined" \
+      raise CliGen::MissingDispatchError.new("CommandNode({{T}})#check! : {{T}} has no subcommands and no #main defined") \
         if subcommands.empty? && !{{T.has_method?(:main)}}
       {% end %}
     end
@@ -199,35 +207,41 @@ module CliGen
             exit 0
             {% end %}
           else
-            raise "ERROR : Couldn't find thing"
+            raise CliGen::UnknownCommandNodeError.new("CommandNode({{T}})#process : matched a BaseCommandNode that isn't a known CommandNode(T)")
           end
           {% end %}
           passed_execution = true
 
         when BaseFlag
-          if match.requires_arg?
-            match.process(args.reject(&.processed?))
-          else
-            match.process
+          # Ensuring we catch any exceptions to have them abort with the
+          # error message if caught
+          handle_flag_raises do
+            if match.requires_arg?
+              match.process(args.reject(&.processed?).take_while{|v| find_match(v.value) == CliGen::MatchType::NoMatch}) 
+            else
+              match.process
+            end
           end
 
         when MatchType::SubCommand
-          raise "ERROR : CommandNode({{T}})#process : Subcommand(#{matched_subcommand}) was already matched" if matched_subcommand
+          raise CliGen::InternalError.new("CommandNode({{T}})#process : subcommand '#{matched_subcommand}' was already matched — duplicate subcommand token") if matched_subcommand
           matched_subcommand = arg.value
 
         when MatchType::Help
-          abort help
+          raise CliGen::HelpRequestedError.new(help)
 
         when MatchType::FlagWithArg
           if regex_match = CliGen::Regex::FLAG_WITH_ARG.match(arg.value)
             case flag_match = find_match(regex_match["flag"])
             when BaseFlag
-              flag_match.process([CliGen::Arg.new(value: regex_match["arg"], index: arg.index)])
+              handle_flag_raises do
+                flag_match.process([CliGen::Arg.new(value: regex_match["arg"], index: arg.index)])
+              end
             else
-              raise "ERROR : CommandNode(#{@name}).process : No flag matched '#{regex_match["flag"]}'"
+              raise CliGen::UnknownCommandNodeError.new("CommandNode(#{@name}).process : No flag matched '#{regex_match["flag"]}'")
             end
           else
-            raise "Oh good, you broke regex. How the hell did it match in find_match but not above? What the hell is going on"
+            raise CliGen::RegexInvariantError.new("CommandNode(#{@name}).process : FLAG_WITH_ARG matched in find_match but failed on re-match — this is a framework bug")
           end
 
         when MatchType::FlagMultipleShort
@@ -236,43 +250,34 @@ module CliGen
           # If the next character in the series is a flag assume the remaining are flags as well.
           if flag?("-#{val[1]}")
             chars = val.chars
-            chars.map { |c| "-#{c}" }.each do |flag|
+            chars.map { |c| "-#{c}" }.each_with_index do |flag, index|
               case match = find_match(flag)
               when BaseFlag
                 # If this is the last flag in the series let it process others
-                if flag == "-#{chars.last}"
-                  if match.requires_arg?
-                    match.process(args.reject(&.processed?))
+                handle_flag_raises do
+                  ## If this is the last flag provided in the clump do the thing
+                  if index == chars.size - 1
+                    if match.requires_arg?
+                      match.process(args.reject(&.processed?).take_while{|v| find_match(v.value) == CliGen::MatchType::NoMatch}) 
+                    else
+                      match.process
+                    end
                   else
+                    raise CliGen::FlagBundleError.new("#{CliGen::APPNAME}: cannot bundle '#{flag}' — it requires an argument") if match.requires_arg?
                     match.process
                   end
-                else
-                  abort "#{CliGen::APPNAME}: cannot bundle flag that requires an argument: #{flag}" if match.requires_arg?
-                  match.process
                 end
               when MatchType::NoMatch
-                abort "ERROR : CommandNode(#{@name}).process : No flag match for '#{flag}'"
+                raise CliGen::UnknownFlagError.new("#{CliGen::APPNAME}: unknown flag '#{flag}'")
               end
             end
           else
             # In this case we assume the characters following the flag is the argument
-            flg = "-#{val[0]}"
-            argument = Arg.new(value: val[1..], index: 0)
-            case match = find_match(flg)
-            when BaseFlag
-              if match.requires_arg?
-                match.process([argument])
-              else
-                abort "ERROR : CommandNode(#{@name}).process : Unknown characters proceeding a boolean flag(#{flg}) : #{val[1..]}"
-              end
-            when MatchType::NoMatch
-              abort "ERROR : CommandNode(#{@name}).process : No flag match for '#{arg.value}'"
-            end
+            raise CliGen::FlagArgumentError.new("#{CliGen::APPNAME}: inline flag arguments are not supported — did you mean '-#{val[0]} #{val[1..]}'?")
           end
 
         when MatchType::NoMatch
-          puts "ERROR : CommandNode(#{@name}).process : No command, subcommand or flag match for '#{arg.value}'"
-          abort help
+          raise CliGen::HelpRequestedError.new("#{CliGen::APPNAME}: unknown token '#{arg.value}'\n\n#{help}")
         end
       end
 
diff --git a/src/cligen/exceptions.cr b/src/cligen/exceptions.cr
new file mode 100644
index 0000000..7927c3d
--- /dev/null
+++ b/src/cligen/exceptions.cr
@@ -0,0 +1,77 @@
+module CliGen
+  # Base for all CliGen exceptions
+  class Error < Exception; end
+
+  # -------------------------------------------------------------------------
+  # Internal errors — framework invariant violations, should never reach users
+  # -------------------------------------------------------------------------
+
+  class InternalError < Error; end
+
+  # Arg#processed was called a second time on the same Arg
+  class ArgReprocessedError < InternalError; end
+
+  # A token matched FLAG_WITH_ARG in find_match but the regex failed on re-match
+  class RegexInvariantError < InternalError; end
+
+  # A BaseCommandNode was matched but couldn't be cast to any known CommandNode(T)
+  class UnknownCommandNodeError < InternalError; end
+
+  # -------------------------------------------------------------------------
+  # Configuration errors — shard consumer wired something up incorrectly
+  # -------------------------------------------------------------------------
+
+  class ConfigurationError < Error; end
+
+  # -h or --help was used as a flag short/long (reserved for internal help)
+  class ReservedFlagError < ConfigurationError; end
+
+  # Duplicate short or long flags detected during check!
+  class DuplicateFlagError < ConfigurationError; end
+
+  # A CommandNode(T) has no subcommands and no #main defined
+  class MissingDispatchError < ConfigurationError; end
+
+  # No flag was found in the handler for a Command ivar during initialize
+  class FlagNotFoundError < ConfigurationError; end
+
+  # A flag that requires an argument was processed with an empty argv
+  class FlagMissingArgumentError < ConfigurationError; end
+
+  # A Parsable type's parse_args did not mark any args as processed
+  class ParseableInvariantError < ConfigurationError; end
+
+  # -------------------------------------------------------------------------
+  # Runtime errors — bad user input at the CLI level
+  # -------------------------------------------------------------------------
+
+  class RuntimeError < Error; end
+
+  # A required flag was not provided and has no env var or default to fall back on
+  class MissingRequiredFlagError < RuntimeError; end
+
+  # A setter's validation proc rejected the provided value
+  class ValidationError < RuntimeError; end
+
+  # A flag token was provided where a value argument was expected
+  class FlagArgumentError < RuntimeError; end
+
+  # A provided value doesn't satisfy type or format requirements (wrong type, bad format, invalid bool/date string)
+  class InvalidFlagValueError < RuntimeError; end
+
+  # A provided value is not in the flag's allowed options list
+  class InvalidOptionError < RuntimeError; end
+
+  # An unrecognised flag token was encountered during parsing
+  class UnknownFlagError < RuntimeError; end
+
+  # A flag that requires an argument was included in a short-flag bundle
+  class FlagBundleError < RuntimeError; end
+
+  # -------------------------------------------------------------------------
+  # Help signal — not an error; exit 0 after printing
+  # -------------------------------------------------------------------------
+
+  # Raised when -h/--help is matched; carries the rendered help string
+  class HelpRequestedError < Error; end
+end
diff --git a/src/cligen/flag.cr b/src/cligen/flag.cr
index 909a3d8..2dc0f9f 100644
--- a/src/cligen/flag.cr
+++ b/src/cligen/flag.cr
@@ -67,10 +67,10 @@ module CliGen
       @on_match   : Proc(Nil)? = nil,
       @format     : ::Regex? = nil
       )
-      {% unless T.has_method? :to_s %}
+      {% unless T.class.has_method? :to_s %}
         {% raise "ERROR : Flag(#{T}) : Error your flag type must have a to_s method" %}
       {% end %}
-      {% if T <= Array %}
+      {% if T < Array %}
         {% elem = T.type_vars.first %}
         {% raise "ERROR : Flag(#{T}) : Error your flag subtype #{elem} must have a to_s method" unless elem.class.has_method? :to_s %}
       {% end %}
@@ -99,14 +99,14 @@ module CliGen
 
     def process(argv : Array(Arg) = [] of Arg) : Nil
       if requires_arg?
-        raise "ERROR : Flag(#{T}, long: #{@long_key}) : Array requires an argument but provided array is empty" if argv.empty?
-        abort "ERROR : Flag(#{T}, long: #{@long_key}) : Provided argument was a flag (#{argv.first.value})" if argv.first.flag?
+        raise CliGen::FlagMissingArgumentError.new("Flag(#{T}, long: #{@long_key}) : requires an argument but provided array is empty") if argv.empty?
+        raise CliGen::FlagArgumentError.new("Flag(#{T}, long: #{@long_key}) : a flag token was provided where a value was expected (got: #{argv.first.value})") if argv.first.flag?
       end
 
 
       {% if T == Bool %}
         @value = true
-      {% elsif T <= Array %}
+      {% elsif T < Array %}
         {% raise "ERROR : Flag(#{T}) : You cannot define multiple types of array entries" if T.type_vars.size > 1 %}
         {% elem = T.type_vars.first %}
         argv.each do |arg|
@@ -119,27 +119,54 @@ module CliGen
               end
             end
           end
-          {% if elem == Int32 %}
-            if arg.value.includes?(@delimiter) 
-              @value = (@value || [] of Int32) + arg.value.split(@delimiter).map(&.to_i32)
+          {% if elem < Int %}
+            {% int_case = elem.stringify =~ /^UInt/ ? "uint?".id : "int?".id %}
+            if arg.value.includes?(@delimiter)
+              @value = (@value || T.new) + arg.value.split(@delimiter).map do |val|
+                val = val.strip
+                unless arg.{{int_case}}(val)
+                  raise CliGen::InvalidFlagValueError.new("Flag({{T}}, long: #{@long_key}) : '#{val}' is not a valid {{elem}}")
+                end
+                {{elem}}.new(val)
+              end
             else
-              abort "ERROR : Flag({{T}}, long: #{@long_key}) : Provided arguemnt(#{arg.value}) was not an integer" unless arg.int?
-              (@value ||= [] of Int32) << arg.value.to_i
+              unless arg.{{int_case}}
+                raise CliGen::InvalidFlagValueError.new("Flag({{T}}, long: #{@long_key}) : '#{arg.value}' is not a valid {{T}}") 
+              end
+              (@value ||= T.new) << {{elem}}.new(arg.value)
+            end
+          {% elsif elem < Float %}
+            if arg.value.includes?(@delimiter)
+              @value = (@value || T.new) + arg.value.split(@delimiter).map do |val|
+                val = val.strip
+                unless CliGen::Arg.float?(val)
+                  raise CliGen::InvalidFlagValueError.new("Flag({{T}}, long: #{@long_key}) : '#{val}' is not a valid {{T}}")
+                end
+                {{elem}}.new(val)
+              end
+            else
+              unless arg.float?
+                raise CliGen::InvalidFlagValueError.new("Flag({{T}}, long: #{@long_key}) : '#{arg.value}' is not a float") 
+              end
+              (@value ||= T.new) << {{elem}}.new(arg.value)
             end
           {% elsif elem == String %}
-            if arg.value.includes?(@delimiter) 
-              @value = (@value || [] of String) + arg.value.split(@delimiter).map{|v|
+            if arg.value.includes?(@delimiter)
+              @value = (@value || [] of String) + arg.value.split(@delimiter).map { |v|
                 unless @format.nil?
-                  abort "ERROR : Flag({{T}}, long: #{@long_key} ) : Provided arguemnt(#{v}) did not match a valid fromat \"#{@format.not_nil!.source}\"" unless v =~ @format
+                  raise CliGen::InvalidFlagValueError.new("Flag({{T}}, long: #{@long_key}) : '#{v}' does not match required format /#{@format.not_nil!.source}/") unless v =~ @format
                 end
                 v
               }
             else
-              (@value ||= [] of String) << arg.value
+              if ! @format.nil? && arg.value !~ @format
+                raise CliGen::InvalidFlagValueError.new("Flag({{T}}, long: #{@long_key}) : '#{arg.value}' does not match required format /#{@format.not_nil!.source}/") 
+              end
+            (@value ||= [] of String) << arg.value
             end
           {% elsif elem.class < CliGen::Coercable %}
-          if arg.value.includes?(@delimiter) 
-            @value = (@value || [] of {{elem}}) + arg.value.split(@delimiter).map{|i| {{elem}}.coerce(i)}
+          if arg.value.includes?(@delimiter)
+            @value = (@value || [] of {{elem}}) + arg.value.split(@delimiter).map { |i| {{elem}}.coerce(i) }
           else
             @value = (@value || [] of {{elem}}) + [({{elem}}.coerce(arg.value))]
           end
@@ -148,16 +175,25 @@ module CliGen
           {% end %}
           arg.processed
         end
-      {% elsif T == Int32 %}
-        abort "ERROR : Flag(#{T}, long: #{@long_key})  : #{argv.first.value} is not an int" unless argv.first.int?
-        @value = argv.first.value.to_i
+      {% elsif T < Int %}
+        {% int_case = T.stringify =~ /^UInt/ ? "uint?".id : "int?".id %}
+        unless argv.first.{{int_case}}
+          raise CliGen::InvalidFlagValueError.new("Flag(#{T}, long: #{@long_key}) : '#{argv.first.value}' is not a valid {{T}}") 
+        end
+        @value = T.new(argv.first.value)
+        argv.first.processed
+      {% elsif T < Float %}
+        unless argv.first.float?
+          raise CliGen::InvalidFlagValueError.new("Flag(#{T}, long: #{@long_key}) : '#{argv.first.value}' is not a valid {{T}}") 
+        end
+        @value = T.new(argv.first.value)
         argv.first.processed
       {% elsif T == Time %}
         @value = parse_time(argv.first.value)
         argv.first.processed
       {% elsif T == String %} # String
-        unless @format.nil?
-          abort "ERROR : Flag(#{T}, long: #{@long_key})  : #{argv.first.value} does not match a correct format #{@format.not_nil!.source}" unless argv.first.value =~ @format
+        if ! @format.nil? && argv.first.value !~ @format
+          raise CliGen::InvalidFlagValueError.new("Flag(#{T}, long: #{@long_key}) : '#{argv.first.value}' does not match required format /#{@format.not_nil!.source}/") 
         end
 
         @value = argv.first.value
@@ -167,7 +203,7 @@ module CliGen
         @value = T.parse_args(argv)
         post_processed = argv.select(&.processed?)
         if processed == post_processed
-          raise "ERROR : Flag({{T}}, long: #{@long_key})#process : Your {{T}}#process_args did not mark processed args as processed. Please check your code"
+          raise CliGen::ParseableInvariantError.new("Flag({{T}}, long: #{@long_key})#process : {{T}}#parse_args did not mark any args as processed")
         end
       {% else %}
         {% raise "ERROR : Flag({{T}}#process : Generic Type #{T} is not supported. To add support you must extend with CliGen::Parsable & implement the class method" %}
@@ -189,7 +225,7 @@ module CliGen
 
       v ||= @default
 
-      raise "#{CliGen::APPNAME}: required flag #{@long_key} was not provided" if v.nil?
+      raise CliGen::MissingRequiredFlagError.new("#{CliGen::APPNAME}: required flag #{@long_key} was not provided") if v.nil?
       v.not_nil!
     end
 
@@ -216,48 +252,66 @@ module CliGen
       if opts = @options
         {% if T < Array %}
           v.each do |v2|
-            abort "#{CliGen::APPNAME}: '#{v2}' is not a valid value for #{@long_key} (valid: #{opts.join(", ")})" unless opts.first.includes?(v2)
+            raise CliGen::InvalidOptionError.new("#{CliGen::APPNAME}: '#{v2}' is not a valid value for #{@long_key} (valid: #{opts.join(", ")})") unless opts.first.includes?(v2)
           end
         {% else %}
-          abort "#{CliGen::APPNAME}: '#{v}' is not a valid value for #{@long_key} (valid: #{opts.join(", ")})" unless opts.includes?(v)
+          raise CliGen::InvalidOptionError.new("#{CliGen::APPNAME}: '#{v}' is not a valid value for #{@long_key} (valid: #{opts.join(", ")})") unless opts.includes?(v)
         {% end %}
       end
 
       if check = @validate
-        abort "#{CliGen::APPNAME}: validation failed for #{@long_key} when testing #{v}" unless check.call(v)
+        raise CliGen::ValidationError.new("#{CliGen::APPNAME}: validation failed for #{@long_key} (got: #{v})") unless check.call(v)
       end
     end
 
     def check! : Nil
-      raise "ERROR : Flag({{T}}, long: #{@long})#check! : -h is reserved for internal help usage" if @short == "-h" 
-      raise "ERROR : Flag({{T}}, long: #{@long})#check! : --help is reserved for internal help usage" if @long_key == "--help"
+      raise CliGen::ReservedFlagError.new("Flag({{T}}, long: #{@long})#check! : -h is reserved for internal help") if @short == "-h"
+      raise CliGen::ReservedFlagError.new("Flag({{T}}, long: #{@long})#check! : --help is reserved for internal help") if @long_key == "--help"
     end
 
     private def coerce(raw : String) : T
       {% if T == Bool %}
         case raw
-        when "t","true","1"
+        when /^(t|true|y|yes|1)$/i
           true
-        when "f","false","0"
+        when /^(f|false|n|no|0)$/i
           false
         else
-          abort "ERROR : Flag({{T}}, long: #{@long_key}) : #{raw} is not a valid boolean identifier" 
+          raise CliGen::InvalidFlagValueError.new("Flag({{T}}, long: #{@long_key}) : '#{raw}' is not a valid boolean (expected: t/f/true/false/y/n/yes/no/1/0)")
         end
-      {% elsif T == Int32 %}
-        raw.to_i
+      {% elsif T < Int %}
+        {% int_case = T.stringify =~ /^UInt/ ? "uint?".id : "int?".id %}
+        unless CliGen::Arg.{{int_case}}(raw)
+          raise CliGen::InvalidFlagValueError.new("Flag({{T}}, long: #{@long_key}) : '#{raw}' is not a valid {{T}}") 
+        end
+        T.new(raw)
+      {% elsif T < Float %}
+        unless CliGen::Arg.float?(raw)
+          raise CliGen::InvalidFlagValueError.new("Flag({{T}}, long: #{@long_key}) : '#{raw}' is not a valid {{T}}") 
+        end
+        T.new(raw)
       {% elsif T == Time %}
         parse_time(raw)
-      {% elsif T <= Array %}
+      {% elsif T < Array %}
         if raw.includes?(@delimiter)
           {% elem = T.type_vars.first %}
           raw.split(@delimiter).map do |val|
             unless @format.nil?
-              abort "ERROR : Flag({{T}}, long: #{@long_key}) : #{val} does not match a valid format" unless val =~ @format
+              raise CliGen::InvalidFlagValueError.new("Flag({{T}}, long: #{@long_key}) : '#{val}' does not match required format /#{@format.not_nil!.source}/") unless val =~ @format
             end
 
-            {% if elem == Int32 %}
-              abort "ERROR : Flag({{T}}, long: #{@long_key}) : #{val} is not an integer" unless val =~ /^[[:digit:]]+$/
-              val.to_i
+            {% if elem < Int %}
+              val = val.strip
+              {% int_case = elem.stringify =~ /^UInt/ ? "uint?".id : "int?".id %}
+              unless CliGen::Arg.{{int_case}}(val)
+                raise CliGen::InvalidFlagValueError.new("Flag({{T}}, long: #{@long_key}) : '#{val}' is not a valid {{elem}}") 
+              end
+              {{elem}}.new(val)
+            {% elsif elem < Float %}
+              unless CliGen::Arg.float?(val)
+                raise CliGen::InvalidFlagValueError.new("Flag({{T}}, long: #{@long_key}) : '#{val}' is not a valid {{elem}}") 
+              end
+              {{elem}}.new(val)
             {% elsif elem == String %}
               val
             {% elsif elem.class < CliGen::Coercable %}
@@ -267,12 +321,20 @@ module CliGen
             {% end %}
           end
         else
-          unless @format.nil?
-            abort "ERROR : Flag({{T}}, long: #{@long_key}) : #{raw} does not match a valid format" unless raw =~ @format
+          if ! @format.nil? && raw !~ @format
+            raise CliGen::InvalidFlagValueError.new("Flag({{T}}, long: #{@long_key}) : '#{raw}' does not match required format /#{@format.not_nil!.source}/") 
           end
-          {% if elem == Int32 %}
-            abort "ERROR : Flag({{T}}, long: #{@long_key}) : #{raw} is not an integer" unless raw =~ /^[[:digit:]]+$/
-            [ raw.to_i ]
+          {% if elem < Int %}
+            {% int_case = elem.stringify =~ /^UInt/ ? "uint?".id : "int?".id %}
+            unless CliGen::Arg.{{int_case}}(raw)
+              raise CliGen::InvalidFlagValueError.new("Flag({{T}}, long: #{@long_key}) : '#{raw}' is not a valid {{elem}}") 
+            end
+            [ {{elem}}.new(raw) ]
+          {% elsif elem < Float %}
+            unless CliGen::Arg.float?(raw)
+              raise CliGen::InvalidFlagValueError.new("Flag({{T}}, long: #{@long_key}) : '#{raw}' is not a valid {{elem}}") 
+            end
+            [ {{elem}}.new(raw) ]
           {% elsif elem == String %}
             [ raw ]
           {% elsif elem.class < CliGen::Coercable %}
@@ -295,7 +357,7 @@ module CliGen
         CliGen::Regex::INPUT_DATETIME_REGEX,
         CliGen::Regex::INPUT_DATE_REGEX
       ]
-      abort "#{CliGen::APPNAME}: invalid date/time format '#{raw}' (expected YYYY-MM-DD or YYYY-MM-DD HH:MM:SS)" unless formats.any? { |f| raw.match(f) }
+      raise CliGen::InvalidFlagValueError.new("#{CliGen::APPNAME}: invalid date/time format '#{raw}' (expected YYYY-MM-DD or YYYY-MM-DD HH:MM:SS)") unless formats.any? { |f| raw.match(f) }
       if raw.match(formats[0])
         Time.parse_local(raw, CliGen::Format::INPUT_DATETIME_FORMAT)
       else
diff --git a/src/cligen/regex.cr b/src/cligen/regex.cr
index 783370d..f3c7587 100644
--- a/src/cligen/regex.cr
+++ b/src/cligen/regex.cr
@@ -5,4 +5,8 @@ module CliGen::Regex
 
   INPUT_DATETIME_REGEX = /^[0-9]{4}-[0-9]{2}-[0-9]{2} [0-9]{2}:[0-9]{2}:[0-9]{2}$/
   INPUT_DATE_REGEX = /^[0-9]{4}-[0-9]{2}-[0-9]{2}$/
+
+  FLOAT = /^[-+]?[[:digit:]]+(\.[[:digit:]]+)?$/
+  UINT = /^[[:digit:]]+$/
+  INT = /^[-+]?[[:digit:]]+$/
 end