diff --git a/include/fennec/format/detail/_format.h b/include/fennec/format/detail/_format.h
index 36ab3fb..d5ae122 100644
--- a/include/fennec/format/detail/_format.h
+++ b/include/fennec/format/detail/_format.h
@@ -43,6 +43,8 @@ struct _format_argimpl {
 	_format_argimpl() {};
 	virtual ~_format_argimpl() {};
 	virtual string format(const format_arg& fmt) = 0;
+	virtual bool   is_integer() = 0;
+	virtual int64_t int_value() = 0;
 };
 
 // Polymorphic template specialization
@@ -53,21 +55,28 @@ struct _format_arg : _format_argimpl {
 	_format_arg(const T& arg) : val(arg) {
 	}
 	virtual ~_format_arg() = default;
-	virtual string format(const format_arg& fmt) {
+	string format(const format_arg& fmt) override {
 		return fennec::forward<string>(fmtr(fmt, val));
 	}
+
+	bool is_integer() override {
+		return is_integral_v<T> or is_convertible_v<T, int64_t>;
+	}
+	virtual int64_t int_value() override {
+		if constexpr(is_integral_v<T>) {
+			return val;
+		} else if constexpr(is_convertible_v<T, int64_t>) {
+			return val;
+		} else {
+			return -1;
+		}
+	}
 };
 
-// Polymorphic template specialization for rvalue_references
+// Polymorphic template specialization for x/r/xr value references
 template<typename T>
-struct _format_arg<T&> : _format_argimpl {
-	formatter<T> fmtr;
-	const T& val;
-	_format_arg(const T& arg) : val(arg) {
-	}
-	virtual ~_format_arg() = default;
-	virtual string format(const format_arg& fmt) {
-		return fennec::forward<string>(fmtr(fmt, val));
+struct _format_arg<T&> : _format_arg<T> {
+	_format_arg(const T& arg) : _format_arg<T>(arg) {
 	}
 };
 
@@ -83,8 +92,59 @@ struct _format_argarray {
 	string format(size_t i, const format_arg& fmt) {
 		return args[i]->format(fmt);
 	}
+
+	bool is_integer(size_t i) {
+		return args[i]->is_integer();
+	}
+
+	int64_t int_value(size_t i) {
+		return args[i]->int_value();
+	}
 };
 
+// checks if character is a valid format type
+constexpr bool _isfmt_t(char c) {
+	switch (c) {
+		default: return false;
+		case 's': case '?': // strings
+		case 'c':           // char
+		case 'd':           // decimal
+		case 'b': case 'B': // binary
+		case 'o':           // octal
+		case 'x': case 'X': // hex
+		case 'a': case 'A': // float hex
+		case 'e': case 'E': // scientific notation
+		case 'f': case 'F': // fixed precision
+		case 'g': case 'G': // general precision
+			return true;
+	}
+}
+
+// checks if character is a valid format int type
+constexpr bool _isfmt_i(char c) {
+	switch (c) {
+		default: return false;
+		case 'd':           // decimal
+		case 'b': case 'B': // binary
+		case 'o':           // octal
+		case 'x': case 'X': // hex
+			return true;
+	}
+}
+
+// checks if character is a valid format float type
+constexpr bool _isfmt_f(char c) {
+	switch (c) {
+		default: return false;
+		case 'a': case 'A': // float hex
+		case 'e': case 'E': // scientific notation
+		case 'f': case 'F': // fixed precision
+		case 'g': case 'G': // general precision
+			return true;
+	}
+
+}
+
 }
 
 #endif // FENNEC_LANG_STRINGS_DETAIL_FORMAT_H
diff --git a/include/fennec/format/format.h b/include/fennec/format/format.h
index dc49a20..f4221d8 100644
--- a/include/fennec/format/format.h
+++ b/include/fennec/format/format.h
@@ -43,15 +43,12 @@ template<typename...ArgsT>
 string format(const cstring& str, ArgsT&&...args) {
 	static constexpr size_t argc = sizeof...(ArgsT);
 	static constexpr format_arg default_fmt = {
-		.fill { // default no fill
-			.c = '\0',
-			.n = 0,
-		},
+		.fill  = ' ',
 		.align = '\0',  // default to locale
-		.sign  = '-',   // default to sign only for negative numbers
+		.sign  = '\0',   // default to sign only for negative numbers
 		.alt   = false, // default no prefix
 		.width = 0,
-		.precision = 0,
+		.precision = 6, // default to 6 sigfigs
 		.type  = '\0',
 	};
 
@@ -63,74 +60,210 @@ string format(const cstring& str, ArgsT&&...args) {
 	detail::_format_argarray<argc> argarray = { fennec::forward<ArgsT>(args)... };
 	string res;
 	size_t i = 0;
-	size_t a = -1;
+	size_t arg_c = -1;
 
 	while (i <= str.length()) {
-		size_t b = str.find('{', i);
-		size_t e = str.find('}', i);
+		size_t brace = str.find('{', i);
+		size_t end = str.find('}', i);
 		format_arg fmt = default_fmt;
 
 		// check for '}}'
-		if (e < b) {
-			if (str[e + 1] == '}') {
-				res += string(str.data() + i, e - i);
-				i = e + 2;
+		if (end < brace) {
+			if (str[end + 1] == '}') {
+				res += string(str.data() + i, end - i);
+				i = end + 2;
 				continue;
 			}
 			assertf(false, "fennec::format syntax error, encountered unexpected '{'")
 		}
 
 		// append string
-		if (b >= str.length()) { // handle end case
+		if (brace >= str.length()) { // handle end case
 			res += string(str.data() + i, str.length() - i);
 			break;
 		}
-		res += string(str.data() + i, b - i);
+		res += string(str.data() + i, brace - i);
 
 		// next brace, validate escape
-		size_t nb = str.find('{', b + 1);
-		if (b + 1 == nb) {
+		size_t next_brace = str.find('{', brace + 1);
+		if (brace + 1 == next_brace) {
 			res += '{';
-			i = nb + 1;
+			i = next_brace + 1;
 			continue;
 		}
 
 		// find contained colon
-		size_t c = str.find(':', b);
+		size_t colon = str.find(':', brace);
 
 		// validate colon and brace location
-		assertf(c < nb or e < nb, "fennec::format syntax error, mismatched '{}'");
+		assertf(colon < next_brace or end < next_brace, "fennec::format syntax error, mismatched '{}'");
 
 		// parse index if present
-		size_t id = min(c, e) - 1;
-		if (id > b) {
-			a = 0;
+		size_t id = min(colon, end) - 1;
+		if (id > brace) {
+			arg_c = 0;
 		} else {
-			++a;
+			++arg_c;
 		}
-		for (size_t j = id, k = 1; j > b; --j, k *= 10) {
+		for (size_t j = id, k = 1; j > brace; --j, k *= 10) {
 			size_t u = (str[j] - '0');
 			assertf(u < 10, "fennec::format syntax error, invalid argument index");
-			a += k * u;
+			arg_c += k * u;
 		}
 
+		// store argument to allow nested replacement fields
+		size_t arg = arg_c;
+
 		// validate index
-		assertf(a < argc, "fennec::format syntax error, invalid argument index");
+		assertf(arg < argc, "fennec::format syntax error, invalid argument index");
 
 		// early return case for no colon
-		if (c > e) {
-			res += argarray.format(a, fmt);
-			i = e + 1;
+		if (colon > end) {
+			res += argarray.format(arg, fmt);
+			i = end + 1;
 			continue;
 		}
 
 		// parse format specifiers
 
+		// we're going to parse right-to-left since the valid combinations
+		// of specifiers change based on the type of the argument
+
+		// first find the matching '}' brace, e is not necessarily the matching brace
+		// since some specifiers allow nested replacement fields
+		size_t spec = colon;
+		while (str[spec + 1] != '}') {
+			if (next_brace < end) { // if the next brace is before the next closing brace
+				spec = end + 1;
+				end = str.find('}', spec);
+				next_brace = str.find('{', spec);
+			} else {
+				spec = end - 1;
+				break;
+			}
+		}
+
+		assert(spec < str.length() - 1 and str[spec+1] == '}', "fennec::format syntax error, mismatched '{}'");
+
+		// check type
+		if (detail::_isfmt_t(str[spec])) {
+			fmt.type = str[spec--];
+		}
+
+		// early return
+		if (spec == colon) {
+			res += argarray.format(arg, fmt);
+			i = end + 1;
+			continue;
+		}
+
+		// search for width and precision
+		size_t x = 0, j = 1;
+		bool   found_decimal = false;
+		size_t num_decimals = 0;
+		bool   is_float_t   = detail::_isfmt_f(fmt.type);
+		bool   is_str_t     = fmt.type == 's';
+		bool   is_integer_t = detail::_isfmt_i(fmt.type);
+
+		// default "precision" for strings should be 0 for no limit
+		if (is_str_t) {
+			fmt.precision = 0;
+		}
+
+		// parse width and precision
+		while (isdigit(str[spec]) or (found_decimal = (str[spec] == '.')) or str[spec] == '{' or str[spec] == '}') {
+			// handle decimal point for precision
+			if (found_decimal) {
+				assertf(is_float_t or is_str_t, "fennec::format syntax error, encountered precision argument on non-floating point format");
+				assertf(num_decimals == 0, "fennec::format syntax error, multiple decimals detected in floating point format");
+				++num_decimals;
+				found_decimal = false;
+
+				fmt.precision = x;
+				x = 0, j = 1;
+				--spec;
+				continue;
+			}
+
+			// check for nested replacement field
+			if (str[spec] == '{') {
+				assertf(str[spec - 1] == '0' or str[spec - 1] == '.' or not isdigit(str[spec - 1]),
+						"fennec::format syntax error, unexpected digit preceding nested replacement field");
+
+				bool prec = str[spec - 1] == '.';
+				size_t sub = str[spec + 1] == '}' ? ++arg_c : x;
+
+				assertf(sub < argc, "fennec::format syntax error, argument index out of range in nested replacement field");
+				assertf(argarray.is_integer(sub), "fennec::format argument error, nested replacement field argument is not convertible to integral type");
+
+				(prec ? fmt.precision : fmt.width) = argarray.int_value(sub);
+			}
+
+			// ignore closing brace for nested replacement fields
+			if (str[spec] == '}') {
+				continue;
+			}
+
+			// crude way to only handle 0 case if 0 is the last digit
+			fmt.fill = str[spec] == '0' ? '0' : ' ';
+
+			// parse the number
+			x += j * (str[spec] - '0');
+			j *= 10;
+			--spec;
+		}
+		if (x != 0) {
+			fmt.width = x;
+		}
+
+		// early return
+		if (spec == colon) {
+			res += argarray.format(arg, fmt);
+			i = end + 1;
+			continue;
+		}
+
+		// check for alt form
+		if (str[spec] == '#') {
+			assertf(is_float_t or is_integer_t, "fennec::format syntax error, encountered alt spec ('#') with non-decimal type");
+			fmt.alt = true;
+			--spec;
+		}
+
+		// check for sign
+		if (str[spec] == '-' or str[spec] == '+' or str[spec] == ' ') {
+			fmt.sign = str[spec];
+			if (str[spec] == ' ') { // handle fill if only space, gets overwritten if encounters fill character
+				fmt.fill = ' ';
+			}
+			--spec;
+		}
+
+		// check for alignment
+		if (str[spec] == '<' or str[spec] == '>' or str[spec] == '^') {
+			fmt.align = str[spec];
+			--spec;
+		}
+
+		// fill character
+		if (str[spec] != ':') {
+			fmt.fill = str[spec];
+			if (str[spec] == ' ') {
+				fmt.sign = fmt.sign == '\0' ? ' ' : fmt.sign;
+			}
+			--spec;
+		}
+
+		// default sign
+		fmt.sign = fmt.sign == '\0' ? '-' : fmt.sign;
+
+		// validate that we handled the entire format arg
+		assertf(spec == colon, "fennec::format syntax error, malformed format string detected, possible double colon");
 
 
 		// add formatted argument
-		res += argarray.format(a, fmt);
-		i = e + 1;
+		res += argarray.format(arg, fmt);
+		i = end + 1;
 	}
 
 	return res;
diff --git a/include/fennec/format/format_arg.h b/include/fennec/format/format_arg.h
index 88e07d1..c16e4c9 100644
--- a/include/fennec/format/format_arg.h
+++ b/include/fennec/format/format_arg.h
@@ -37,10 +37,7 @@ namespace fennec
 {
 
 struct format_arg {
-	struct {
-		char   c;
-		size_t n;
-	} fill;
+	char fill;
 	char align, sign;
 	bool alt;
 	size_t width, precision;
diff --git a/include/fennec/format/formatter.h b/include/fennec/format/formatter.h
index 218b205..ebcf47b 100644
--- a/include/fennec/format/formatter.h
+++ b/include/fennec/format/formatter.h
@@ -37,6 +37,11 @@
 namespace fennec
 {
 
+// base template =======================================================================================================
+
+///
+/// \brief Formatter struct, used to turn values into formatted strings
+/// \tparam T The type to format
 template<typename T>
 struct formatter {
 	string operator()(const format_arg&, const T&) {
@@ -45,6 +50,9 @@ struct formatter {
 	}
 };
 
+
+// strings =============================================================================================================
+
 template<size_t N>
 struct formatter<const char[N]> {
 	string operator()(const format_arg&, const char (&str)[N]) {
@@ -66,6 +74,138 @@ struct formatter<string> {
 	}
 };
 
+
+// decimal types =======================================================================================================
+
+template<typename IntT> requires(is_integral_v<IntT> and not is_bool_v<IntT>)
+struct formatter<IntT> {
+	string operator()(const format_arg& fmt, IntT x) {
+		static constexpr char lowdigits[] = "0123456789abcdef";
+		static constexpr char highdigits[] = "0123456789ABCDEF";
+		bool neg = x < 0; x = fennec::abs(x);
+		const char* digits = lowdigits;
+		string res;
+		string pre;
+
+		size_t base;
+		switch (fmt.type) {
+			// decimal
+			default:
+				assertf(false, "invalid format type for integral value");
+			[[fallthrough]];
+			case '\0': case 'd':
+				base = 10;
+				break;
+
+			// binary
+			case 'B':
+				pre = "0B";
+				base = 2;
+				break;
+			case 'b':
+				pre = "0b";
+				base = 2;
+				break;
+
+			// octal
+			case 'o':
+				pre = "0";
+				base = 8;
+				break;
+
+			// hex
+			case 'X':
+				digits = highdigits;
+				pre = "0X";
+				base = 16;
+				break;
+
+			case 'x':
+				pre = "0x";
+				base = 16;
+				break;
+		}
+
+		// parse int
+		while (x != 0) {
+			res = digits[x % base] + res;
+			x /= base;
+		}
+
+		// handle 0
+		if (res.empty()) {
+			res = '0' + res;
+		}
+
+		// add prefix unless fill is '0'
+		if (fmt.alt and fmt.fill != '0' and (base != 8 or res[0] != '0')) {
+			res = pre + res;
+		}
+
+		// fill
+		size_t fill = fmt.alt ? fmt.width - pre.length() : fmt.width;
+		switch (fmt.align) {
+			// align left
+			case '<':
+				while (res.size() < fill) {
+					res += fmt.fill == '0' ? ' ' : fmt.fill;
+				}
+				break;
+
+			// align right
+			case '>': default:
+				while (res.size() < fill) {
+					res = fmt.fill + res;
+				}
+				break;
+
+			// align
+			case '^':
+				bool rr = true;
+				while (res.size() < fill) {
+					if (rr) {
+						res += fmt.fill == '0' ? ' ' : fmt.fill;
+					} else {
+						res = fmt.fill + res;
+					}
+					rr = !rr;
+				}
+				break;
+		}
+
+		// add prefix after filled 0s
+		if (fmt.alt and fmt.fill == '0') {
+			res = pre + res;
+		}
+
+		// add sign
+		switch (fmt.sign) {
+			case '+':
+				res = (neg ? '-' : '+') + res;
+				break;
+			case ' ':
+				res = (neg ? '-' : ' ') + res;
+				break;
+			case '-': default:
+				if (neg) res = '-' + res;
+				break;
+		}
+
+		return res;
+	}
+};
+
+template<typename BoolT> requires(is_bool_v<BoolT>)
+struct formatter<BoolT> {
+	string operator()(const format_arg& fmt, BoolT x) {
+		if (fmt.type == 's' or fmt.type == '\0') {
+			return x ? string("true") : string("false");
+		}
+
+		return formatter<uint8_t>{}(fmt, static_cast<uint8_t>(x));
+	}
+};
+
 }
 
 #endif // FENNEC_LANG_FORMAT_FORMATTER_H
\ No newline at end of file
diff --git a/include/fennec/string/string.h b/include/fennec/string/string.h
index 88b2fda..54a79e0 100644
--- a/include/fennec/string/string.h
+++ b/include/fennec/string/string.h
@@ -19,11 +19,8 @@
 #ifndef FENNEC_LANGPROC_STRINGS_STRING_H
 #define FENNEC_LANGPROC_STRINGS_STRING_H
 
-#include <fennec/string/detail/_ctype.h>
 #include <fennec/string/cstring.h>
 
-#include <fennec/lang/assert.h>
-
 #include <fennec/memory/allocator.h>
 #include <fennec/memory/common.h>
 
diff --git a/test/tests/test_format.h b/test/tests/test_format.h
index bd787d8..09a9023 100644
--- a/test/tests/test_format.h
+++ b/test/tests/test_format.h
@@ -47,6 +47,33 @@ inline void fennec_test_format() {
 	fennec_test_run(fennec::format("{0} {0}", "Hello"),           string("Hello Hello"));
 	fennec_test_run(fennec::format("{0} {1}", "Hello", "World!"), string("Hello World!"));
 	fennec_test_run(fennec::format("{1} {0}", "Hello", "World!"), string("World! Hello"));
+
+	fennec_test_spacer(1);
+
+	fennec_test_run(fennec::format("{:6}",   342),  string("   342"));
+	fennec_test_run(fennec::format("{:06}",  342),  string("000342"));
+	fennec_test_run(fennec::format("{:*<6}", 342),  string("342***"));
+	fennec_test_run(fennec::format("{:*>6}", 342),  string("***342"));
+	fennec_test_run(fennec::format("{:*^6}", 342),  string("*342**"));
+
+	fennec_test_spacer(1);
+
+	fennec_test_run(fennec::format("{0:},{0:+},{0:-},{0: }", 1),  string("1,+1,1, 1"));
+	fennec_test_run(fennec::format("{0:},{0:+},{0:-},{0: }", -1), string("-1,-1,-1,-1"));
+
+	fennec_test_spacer(1);
+
+	fennec_test_run(fennec::format("{:#06d}", 15), string("000015"));
+	fennec_test_run(fennec::format("{:#06x}", 15), string("0x000f"));
+	fennec_test_run(fennec::format("{:#06X}", 15), string("0X000F"));
+	fennec_test_run(fennec::format("{:#06o}", 15), string("000017"));
+	fennec_test_run(fennec::format("{:#06b}", 15), string("0b1111"));
+	fennec_test_run(fennec::format("{:#06B}", 15), string("0B1111"));
+
+	fennec_test_spacer(1);
+
+	fennec_test_run(fennec::format("{},{}",           true, false), string("true,false"));
+	fennec_test_run(fennec::format("{:#06b},{:#06b}", true, false), string("0b0001,0b0000"));
 }
 
 }