diff --git a/lib/src/functions/text.dart b/lib/src/functions/text.dart
new file mode 100644
index 0000000..a96b4ea
--- /dev/null
+++ b/lib/src/functions/text.dart
@@ -0,0 +1,230 @@
+import 'dart:math' as math;
+
+import '../evaluator.dart';
+import '../format.dart';
+import '../values.dart';
+import 'helpers.dart';
+
+void registerText(Map<String, CellFunction> registry) {
+  registry['CONCAT'] = (args, ctx) {
+    final buffer = StringBuffer();
+    for (final value in ctx.flatten(args)) {
+      buffer.write(ctx.asText(value));
+    }
+    return TextValue(buffer.toString());
+  };
+  registry['CONCATENATE'] = registry['CONCAT']!;
+
+  registry['TEXTJOIN'] = (args, ctx) {
+    arity(args, 3);
+    final delimiter = textArg(args[0], ctx);
+    final ignoreEmpty = boolArg(args[1], ctx);
+    final parts = <String>[];
+    for (final value in ctx.flatten(args.sublist(2))) {
+      final text = ctx.asText(value);
+      if (ignoreEmpty && text.isEmpty) continue;
+      parts.add(text);
+    }
+    return TextValue(parts.join(delimiter));
+  };
+
+  registry['LEN'] = (args, ctx) {
+    arity(args, 1, 1);
+    return NumberValue(textArg(args[0], ctx).length.toDouble());
+  };
+
+  registry['LEFT'] = (args, ctx) {
+    arity(args, 1, 2);
+    final text = textArg(args[0], ctx);
+    final count = args.length > 1 ? intArg(args[1], ctx) : 1;
+    if (count < 0) throw const EvalException(ErrorValue(ErrorKind.value));
+    return TextValue(text.substring(0, math.min(count, text.length)));
+  };
+
+  registry['RIGHT'] = (args, ctx) {
+    arity(args, 1, 2);
+    final text = textArg(args[0], ctx);
+    final count = args.length > 1 ? intArg(args[1], ctx) : 1;
+    if (count < 0) throw const EvalException(ErrorValue(ErrorKind.value));
+    final take = math.min(count, text.length);
+    return TextValue(text.substring(text.length - take));
+  };
+
+  registry['MID'] = (args, ctx) {
+    arity(args, 3, 3);
+    final text = textArg(args[0], ctx);
+    final start = intArg(args[1], ctx);
+    final length = intArg(args[2], ctx);
+    if (start < 1 || length < 0) throw const EvalException(ErrorValue(ErrorKind.value));
+    if (start > text.length) return const TextValue('');
+    final begin = start - 1;
+    final end = math.min(begin + length, text.length);
+    return TextValue(text.substring(begin, end));
+  };
+
+  registry['UPPER'] = (args, ctx) {
+    arity(args, 1, 1);
+    return TextValue(textArg(args[0], ctx).toUpperCase());
+  };
+
+  registry['LOWER'] = (args, ctx) {
+    arity(args, 1, 1);
+    return TextValue(textArg(args[0], ctx).toLowerCase());
+  };
+
+  registry['PROPER'] = (args, ctx) {
+    arity(args, 1, 1);
+    final text = textArg(args[0], ctx);
+    final buffer = StringBuffer();
+    var atWordStart = true;
+    for (final rune in text.runes) {
+      final ch = String.fromCharCode(rune);
+      final isLetter = RegExp(r'[A-Za-z]').hasMatch(ch);
+      if (isLetter) {
+        buffer.write(atWordStart ? ch.toUpperCase() : ch.toLowerCase());
+        atWordStart = false;
+      } else {
+        buffer.write(ch);
+        atWordStart = true;
+      }
+    }
+    return TextValue(buffer.toString());
+  };
+
+  registry['TRIM'] = (args, ctx) {
+    arity(args, 1, 1);
+    return TextValue(textArg(args[0], ctx).trim().replaceAll(RegExp(r'\s+'), ' '));
+  };
+
+  registry['REPT'] = (args, ctx) {
+    arity(args, 2, 2);
+    final count = intArg(args[1], ctx);
+    if (count < 0) throw const EvalException(ErrorValue(ErrorKind.value));
+    return TextValue(textArg(args[0], ctx) * count);
+  };
+
+  registry['EXACT'] = (args, ctx) {
+    arity(args, 2, 2);
+    return BooleanValue(textArg(args[0], ctx) == textArg(args[1], ctx));
+  };
+
+  registry['SUBSTITUTE'] = (args, ctx) {
+    arity(args, 3, 4);
+    final text = textArg(args[0], ctx);
+    final oldText = textArg(args[1], ctx);
+    final newText = textArg(args[2], ctx);
+    if (oldText.isEmpty) return TextValue(text);
+    if (args.length == 3) return TextValue(text.replaceAll(oldText, newText));
+    final instance = intArg(args[3], ctx);
+    if (instance < 1) throw const EvalException(ErrorValue(ErrorKind.value));
+    return TextValue(_replaceNth(text, oldText, newText, instance));
+  };
+
+  registry['REPLACE'] = (args, ctx) {
+    arity(args, 4, 4);
+    final text = textArg(args[0], ctx);
+    final start = intArg(args[1], ctx);
+    final length = intArg(args[2], ctx);
+    final replacement = textArg(args[3], ctx);
+    if (start < 1 || length < 0) throw const EvalException(ErrorValue(ErrorKind.value));
+    final begin = math.min(start - 1, text.length);
+    final end = math.min(begin + length, text.length);
+    return TextValue(text.substring(0, begin) + replacement + text.substring(end));
+  };
+
+  registry['FIND'] = (args, ctx) {
+    arity(args, 2, 3);
+    final needle = textArg(args[0], ctx);
+    final haystack = textArg(args[1], ctx);
+    final start = args.length > 2 ? intArg(args[2], ctx) : 1;
+    if (start < 1) throw const EvalException(ErrorValue(ErrorKind.value));
+    final index = haystack.indexOf(needle, start - 1);
+    if (index < 0) throw const EvalException(ErrorValue(ErrorKind.value));
+    return NumberValue((index + 1).toDouble());
+  };
+
+  registry['SEARCH'] = (args, ctx) {
+    arity(args, 2, 3);
+    final needle = textArg(args[0], ctx).toLowerCase();
+    final haystack = textArg(args[1], ctx).toLowerCase();
+    final start = args.length > 2 ? intArg(args[2], ctx) : 1;
+    if (start < 1) throw const EvalException(ErrorValue(ErrorKind.value));
+    final index = haystack.indexOf(needle, start - 1);
+    if (index < 0) throw const EvalException(ErrorValue(ErrorKind.value));
+    return NumberValue((index + 1).toDouble());
+  };
+
+  registry['CHAR'] = (args, ctx) {
+    arity(args, 1, 1);
+    final code = intArg(args[0], ctx);
+    if (code < 1 || code > 0x10FFFF) throw const EvalException(ErrorValue(ErrorKind.value));
+    return TextValue(String.fromCharCode(code));
+  };
+
+  registry['CODE'] = (args, ctx) {
+    arity(args, 1, 1);
+    final text = textArg(args[0], ctx);
+    if (text.isEmpty) throw const EvalException(ErrorValue(ErrorKind.value));
+    return NumberValue(text.runes.first.toDouble());
+  };
+
+  registry['VALUE'] = (args, ctx) {
+    arity(args, 1, 1);
+    final parsed = double.tryParse(textArg(args[0], ctx).trim());
+    if (parsed == null) throw const EvalException(ErrorValue(ErrorKind.value));
+    return NumberValue(parsed);
+  };
+
+  registry['NUMBERVALUE'] = (args, ctx) {
+    arity(args, 1, 3);
+    var text = textArg(args[0], ctx).trim();
+    final decimalSep = args.length > 1 ? textArg(args[1], ctx) : '.';
+    final groupSep = args.length > 2 ? textArg(args[2], ctx) : ',';
+    text = text.replaceAll(groupSep, '');
+    if (decimalSep != '.') text = text.replaceAll(decimalSep, '.');
+    final parsed = double.tryParse(text);
+    if (parsed == null) throw const EvalException(ErrorValue(ErrorKind.value));
+    return NumberValue(parsed);
+  };
+
+  registry['TEXT'] = (args, ctx) {
+    arity(args, 2, 2);
+    final value = ctx.eval(args[0]);
+    final code = textArg(args[1], ctx);
+    return TextValue(NumberFormat.fromCode(code).apply(value));
+  };
+
+  registry['REGEXMATCH'] = (args, ctx) {
+    arity(args, 2, 2);
+    final pattern = RegExp(textArg(args[1], ctx));
+    return BooleanValue(pattern.hasMatch(textArg(args[0], ctx)));
+  };
+
+  registry['REGEXEXTRACT'] = (args, ctx) {
+    arity(args, 2, 2);
+    final pattern = RegExp(textArg(args[1], ctx));
+    final match = pattern.firstMatch(textArg(args[0], ctx));
+    if (match == null) throw const EvalException(ErrorValue(ErrorKind.na));
+    return TextValue(match.groupCount >= 1 ? (match.group(1) ?? '') : match.group(0)!);
+  };
+
+  registry['REGEXREPLACE'] = (args, ctx) {
+    arity(args, 3, 3);
+    final pattern = RegExp(textArg(args[1], ctx));
+    return TextValue(textArg(args[0], ctx).replaceAll(pattern, textArg(args[2], ctx)));
+  };
+}
+
+String _replaceNth(String text, String oldText, String newText, int instance) {
+  var searchFrom = 0;
+  var seen = 0;
+  while (true) {
+    final index = text.indexOf(oldText, searchFrom);
+    if (index < 0) return text;
+    seen++;
+    if (seen == instance) {
+      return text.substring(0, index) + newText + text.substring(index + oldText.length);
+    }
+    searchFrom = index + oldText.length;
+  }
+}