diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..5c60afe
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,26 @@
+Copyright 2014, the Dart project authors. All rights reserved.
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google Inc. nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..90660fc
--- /dev/null
+++ b/README.md
@@ -0,0 +1,37 @@
+This package exposes a `StringScanner` type that makes it easy to parse a string
+using a series of `Pattern`s. For example:
+
+```dart
+import 'dart:math';
+
+import 'package:string_scanner/string_scanner.dart';
+
+num parseNumber(String source) {
+  // Scan a number ("1", "1.5", "-3").
+  var scanner = new StringScanner(source);
+
+  // [Scanner.scan] tries to consume a [Pattern] and returns whether or not it
+  // succeeded. It will move the scan pointer past the end of the pattern.
+  var negative = scanner.scan("-");
+
+  // [Scanner.expect] consumes a [Pattern] and throws a [FormatError] if it
+  // fails. Like [Scanner.scan], it will move the scan pointer forward.
+  scanner.expect(new RegExp(r"\d+"));
+
+  // [Scanner.lastMatch] holds the [MatchData] for the most recent call to
+  // [Scanner.scan], [Scanner.expect], or [Scanner.matches].
+  var number = int.parse(scanner.lastMatch[0]);
+
+  if (scanner.scan(".")) {
+    scanner.expect(new RegExp(r"\d+"));
+    var decimal = scanner.lastMatch[0];
+    number += int.parse(decimal) / math.pow(10, decimal.length);
+  }
+
+  // [Scanner.expectDone] will throw a [FormatError] if there's any input that
+  // hasn't yet been consumed.
+  scanner.expectDone();
+
+  return (negative ? -1 : 1) * number;
+}
+```
diff --git a/lib/string_scanner.dart b/lib/string_scanner.dart
new file mode 100644
index 0000000..624c090
--- /dev/null
+++ b/lib/string_scanner.dart
@@ -0,0 +1,113 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// A library for parsing strings using a sequence of patterns.
+library string_scanner;
+
+// TODO(nweiz): Add some integration between this and source maps.
+/// A class that scans through a string using [Pattern]s.
+class StringScanner {
+  /// The string being scanned through.
+  final String string;
+
+  /// The current position of the scanner in the string, in characters.
+  int get position => _position;
+  set position(int position) {
+    if (position < 0 || position > string.length) {
+      throw new ArgumentError("Invalid position $position");
+    }
+
+    _position = position;
+  }
+  int _position = 0;
+
+  /// The data about the previous match made by the scanner.
+  ///
+  /// If the last match failed, this will be `null`.
+  Match get lastMatch => _lastMatch;
+  Match _lastMatch;
+
+  /// The portion of the string that hasn't yet been scanned.
+  String get rest => string.substring(position);
+
+  /// Whether the scanner has completely consumed [string].
+  bool get isDone => position == string.length;
+
+  /// Creates a new [StringScanner] that starts scanning from [position].
+  ///
+  /// [position] defaults to 0, the beginning of the string.
+  StringScanner(this.string, {int position}) {
+    if (position != null) this.position = position;
+  }
+
+  /// If [pattern] matches at the current position of the string, scans forward
+  /// until the end of the match.
+  ///
+  /// Returns whether or not [pattern] matched.
+  bool scan(Pattern pattern) {
+    var success = matches(pattern);
+    if (success) _position = _lastMatch.end;
+    return success;
+  }
+
+  /// If [pattern] matches at the current position of the string, scans forward
+  /// until the end of the match.
+  ///
+  /// If [pattern] did not match, throws a [FormatException] describing the
+  /// position of the failure. [name] is used in this error as the expected name
+  /// of the pattern being matched; if it's `null`, the pattern itself is used
+  /// instead.
+  void expect(Pattern pattern, {String name}) {
+    if (scan(pattern)) return;
+
+    if (name == null) {
+      if (pattern is RegExp) {
+        name = "/${pattern.pattern.replaceAll("/", "\\/")}/";
+      } else {
+        name = pattern.toString()
+            .replaceAll("\\", "\\\\").replaceAll('"', '\\"');
+        name = '"$name"';
+      }
+    }
+    _fail(name);
+  }
+
+  /// If the string has not been fully consumed, this throws a
+  /// [FormatException].
+  void expectDone() {
+    if (isDone) return;
+    _fail("no more input");
+  }
+
+  /// Returns whether or not [pattern] matches at the current position of the
+  /// string.
+  ///
+  /// This doesn't move the scan pointer forward.
+  bool matches(Pattern pattern) {
+    _lastMatch = pattern.matchAsPrefix(string, position);
+    return _lastMatch != null;
+  }
+
+  // TODO(nweiz): Make this handle long lines more gracefully.
+  /// Throws a [FormatException] describing that [name] is expected at the
+  /// current position in the string.
+  void _fail(String name) {
+    var newlines = "\n".allMatches(string.substring(0, position)).toList();
+    var line = newlines.length + 1;
+    var column;
+    var lastLine;
+    if (newlines.isEmpty) {
+      column = position + 1;
+      lastLine = string.substring(0, position);
+    } else {
+      column = position - newlines.last.end + 1;
+      lastLine = string.substring(newlines.last.end, position);
+    }
+    lastLine += rest.replaceFirst(new RegExp(r"\n.*"), '');
+    throw new FormatException(
+        "Expected $name on line $line, column $column.\n"
+        "$lastLine\n"
+        "${new List.filled(column - 1, ' ').join()}^");
+  }
+}
diff --git a/pubspec.yaml b/pubspec.yaml
new file mode 100644
index 0000000..3035901
--- /dev/null
+++ b/pubspec.yaml
@@ -0,0 +1,10 @@
+name: string_scanner
+version: 0.0.1
+author: "Dart Team <misc@dartlang.org>"
+homepage: http://www.dartlang.org
+description: >
+  A class for parsing strings using a sequence of patterns.
+dev_dependencies:
+  unittest: ">=0.10.0 <0.11.0"
+environment:
+  sdk: ">=1.2.0 <2.0.0"
diff --git a/test/error_format_test.dart b/test/error_format_test.dart
new file mode 100644
index 0000000..1187344
--- /dev/null
+++ b/test/error_format_test.dart
@@ -0,0 +1,110 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library string_scanner.error_format_test;
+
+import 'package:string_scanner/string_scanner.dart';
+import 'package:unittest/unittest.dart';
+
+void main() {
+  test('points to the first unconsumed character', () {
+    var scanner = new StringScanner('foo bar baz');
+    scanner.expect('foo ');
+    expect(() => scanner.expect('foo'), throwsFormattedError('''
+Expected "foo" on line 1, column 5.
+foo bar baz
+    ^'''));
+  });
+
+  test('prints the correct line', () {
+    var scanner = new StringScanner('foo bar baz\ndo re mi\nearth fire water');
+    scanner.expect('foo bar baz\ndo ');
+    expect(() => scanner.expect('foo'), throwsFormattedError('''
+Expected "foo" on line 2, column 4.
+do re mi
+   ^'''));
+  });
+
+  test('handles the beginning of the string correctly', () {
+    var scanner = new StringScanner('foo bar baz');
+    expect(() => scanner.expect('zap'), throwsFormattedError('''
+Expected "zap" on line 1, column 1.
+foo bar baz
+^'''));
+  });
+
+  test('handles the end of the string correctly', () {
+    var scanner = new StringScanner('foo bar baz');
+    scanner.expect('foo bar baz');
+    expect(() => scanner.expect('bang'), throwsFormattedError('''
+Expected "bang" on line 1, column 12.
+foo bar baz
+           ^'''));
+  });
+
+  test('handles an empty string correctly', () {
+    expect(() => new StringScanner('').expect('foo'), throwsFormattedError('''
+Expected "foo" on line 1, column 1.
+
+^'''));
+  });
+
+  group("expected name", () {
+    test("uses the provided name", () {
+      expect(() => new StringScanner('').expect('foo bar', name: 'zap'),
+          throwsFormattedError('''
+Expected zap on line 1, column 1.
+
+^'''));
+    });
+
+    test("escapes string quotes", () {
+      expect(() => new StringScanner('').expect('foo"bar'),
+          throwsFormattedError('''
+Expected "foo\\"bar" on line 1, column 1.
+
+^'''));
+    });
+
+    test("escapes string backslashes", () {
+      expect(() => new StringScanner('').expect('foo\\bar'),
+          throwsFormattedError('''
+Expected "foo\\\\bar" on line 1, column 1.
+
+^'''));
+    });
+
+    test("prints PERL-style regexps", () {
+      expect(() => new StringScanner('').expect(new RegExp(r'foo')),
+          throwsFormattedError('''
+Expected /foo/ on line 1, column 1.
+
+^'''));
+    });
+
+    test("escape regexp forward slashes", () {
+      expect(() => new StringScanner('').expect(new RegExp(r'foo/bar')),
+          throwsFormattedError('''
+Expected /foo\\/bar/ on line 1, column 1.
+
+^'''));
+    });
+
+    test("does not escape regexp backslashes", () {
+      expect(() => new StringScanner('').expect(new RegExp(r'foo\bar')),
+          throwsFormattedError('''
+Expected /foo\\bar/ on line 1, column 1.
+
+^'''));
+    });
+  });
+}
+
+Matcher throwsFormattedError(String format) {
+  return throwsA(predicate((error) {
+    expect(error, isFormatException);
+    expect(error.message, equals(format));
+    return true;
+  }));
+}
diff --git a/test/string_scanner_test.dart b/test/string_scanner_test.dart
new file mode 100644
index 0000000..0cab627
--- /dev/null
+++ b/test/string_scanner_test.dart
@@ -0,0 +1,267 @@
+// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library string_scanner.string_scanner_test;
+
+import 'package:string_scanner/string_scanner.dart';
+import 'package:unittest/unittest.dart';
+
+void main() {
+  group('with an empty string', () {
+    var scanner;
+    setUp(() {
+      scanner = new StringScanner('');
+    });
+
+    test('is done', () {
+      expect(scanner.isDone, isTrue);
+      expect(scanner.expectDone, isNot(throwsFormatException));
+    });
+
+    test('rest is empty', () {
+      expect(scanner.rest, isEmpty);
+    });
+
+    test('lastMatch is null', () {
+      expect(scanner.lastMatch, isNull);
+    });
+
+    test('position is zero', () {
+      expect(scanner.position, equals(0));
+    });
+
+    test("scan returns false and doesn't change the state", () {
+      expect(scanner.scan(new RegExp('.')), isFalse);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test("expect throws a FormatException and doesn't change the state", () {
+      expect(() => scanner.expect(new RegExp('.')), throwsFormatException);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test("matches returns false and doesn't change the state", () {
+      expect(scanner.matches(new RegExp('.')), isFalse);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+    });
+
+    test('setting position to 1 throws an ArgumentError', () {
+      expect(() {
+        scanner.position = 1;
+      }, throwsArgumentError);
+    });
+
+    test('setting position to -1 throws an ArgumentError', () {
+      expect(() {
+        scanner.position = -1;
+      }, throwsArgumentError);
+    });
+  });
+
+  group('at the beginning of a string', () {
+    var scanner;
+    setUp(() {
+      scanner = new StringScanner('foo bar');
+    });
+
+    test('is not done', () {
+      expect(scanner.isDone, isFalse);
+      expect(scanner.expectDone, throwsFormatException);
+    });
+
+    test('rest is the whole string', () {
+      expect(scanner.rest, equals('foo bar'));
+    });
+
+    test('lastMatch is null', () {
+      expect(scanner.lastMatch, isNull);
+    });
+
+    test('position is zero', () {
+      expect(scanner.position, equals(0));
+    });
+
+    test("a matching scan returns true and changes the state", () {
+      expect(scanner.scan(new RegExp('f(..)')), isTrue);
+      expect(scanner.lastMatch[1], equals('oo'));
+      expect(scanner.position, equals(3));
+      expect(scanner.rest, equals(' bar'));
+    });
+
+    test("a non-matching scan returns false and sets lastMatch to null", () {
+      expect(scanner.matches(new RegExp('f(..)')), isTrue);
+      expect(scanner.lastMatch, isNotNull);
+
+      expect(scanner.scan(new RegExp('b(..)')), isFalse);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+      expect(scanner.rest, equals('foo bar'));
+    });
+
+    test("a matching expect changes the state", () {
+      scanner.expect(new RegExp('f(..)'));
+      expect(scanner.lastMatch[1], equals('oo'));
+      expect(scanner.position, equals(3));
+      expect(scanner.rest, equals(' bar'));
+    });
+
+    test("a non-matching expect throws a FormatException and sets lastMatch to "
+        "null", () {
+      expect(scanner.matches(new RegExp('f(..)')), isTrue);
+      expect(scanner.lastMatch, isNotNull);
+
+      expect(() => scanner.expect(new RegExp('b(..)')), throwsFormatException);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+      expect(scanner.rest, equals('foo bar'));
+    });
+
+    test("a matching matches returns true and only changes lastMatch", () {
+      expect(scanner.matches(new RegExp('f(..)')), isTrue);
+      expect(scanner.lastMatch[1], equals('oo'));
+      expect(scanner.position, equals(0));
+      expect(scanner.rest, equals('foo bar'));
+    });
+
+    test("a non-matching matches returns false and doesn't change the state",
+        () {
+      expect(scanner.matches(new RegExp('b(..)')), isFalse);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(0));
+      expect(scanner.rest, equals('foo bar'));
+    });
+
+    test('setting position to 1 moves the cursor forward', () {
+      scanner.position = 1;
+      expect(scanner.position, equals(1));
+      expect(scanner.rest, equals('oo bar'));
+
+      expect(scanner.scan(new RegExp('oo.')), isTrue);
+      expect(scanner.lastMatch[0], equals('oo '));
+      expect(scanner.position, equals(4));
+      expect(scanner.rest, equals('bar'));
+    });
+
+    test('setting position beyond the string throws an ArgumentError', () {
+      expect(() {
+        scanner.position = 8;
+      }, throwsArgumentError);
+    });
+
+    test('setting position to -1 throws an ArgumentError', () {
+      expect(() {
+        scanner.position = -1;
+      }, throwsArgumentError);
+    });
+
+    test('scan accepts any Pattern', () {
+      expect(scanner.scan('foo'), isTrue);
+      expect(scanner.lastMatch[0], equals('foo'));
+      expect(scanner.position, equals(3));
+      expect(scanner.rest, equals(' bar'));
+    });
+
+    test('scans multiple times', () {
+      expect(scanner.scan(new RegExp('f(..)')), isTrue);
+      expect(scanner.lastMatch[1], equals('oo'));
+      expect(scanner.position, equals(3));
+      expect(scanner.rest, equals(' bar'));
+
+      expect(scanner.scan(new RegExp(' b(..)')), isTrue);
+      expect(scanner.lastMatch[1], equals('ar'));
+      expect(scanner.position, equals(7));
+      expect(scanner.rest, equals(''));
+      expect(scanner.isDone, isTrue);
+      expect(scanner.expectDone, isNot(throwsFormatException));
+    });
+  });
+
+  group('at the end of a string', () {
+    var scanner;
+    setUp(() {
+      scanner = new StringScanner('foo bar');
+      expect(scanner.scan('foo bar'), isTrue);
+    });
+
+    test('is done', () {
+      expect(scanner.isDone, isTrue);
+      expect(scanner.expectDone, isNot(throwsFormatException));
+    });
+
+    test('rest is empty', () {
+      expect(scanner.rest, isEmpty);
+    });
+
+    test('position is zero', () {
+      expect(scanner.position, equals(7));
+    });
+
+    test("scan returns false and sets lastMatch to null", () {
+      expect(scanner.scan(new RegExp('.')), isFalse);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(7));
+    });
+
+    test("expect throws a FormatException and sets lastMatch to null", () {
+      expect(() => scanner.expect(new RegExp('.')), throwsFormatException);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(7));
+    });
+
+    test("matches returns false sets lastMatch to null", () {
+      expect(scanner.matches(new RegExp('.')), isFalse);
+      expect(scanner.lastMatch, isNull);
+      expect(scanner.position, equals(7));
+    });
+
+    test('setting position to 1 moves the cursor backward', () {
+      scanner.position = 1;
+      expect(scanner.position, equals(1));
+      expect(scanner.rest, equals('oo bar'));
+
+      expect(scanner.scan(new RegExp('oo.')), isTrue);
+      expect(scanner.lastMatch[0], equals('oo '));
+      expect(scanner.position, equals(4));
+      expect(scanner.rest, equals('bar'));
+    });
+
+    test('setting position beyond the string throws an ArgumentError', () {
+      expect(() {
+        scanner.position = 8;
+      }, throwsArgumentError);
+    });
+
+    test('setting position to -1 throws an ArgumentError', () {
+      expect(() {
+        scanner.position = -1;
+      }, throwsArgumentError);
+    });
+  });
+
+  group('a scanner constructed with a custom position', () {
+    test('starts scanning from that position', () {
+      var scanner = new StringScanner('foo bar', position: 1);
+      expect(scanner.position, equals(1));
+      expect(scanner.rest, equals('oo bar'));
+
+      expect(scanner.scan(new RegExp('oo.')), isTrue);
+      expect(scanner.lastMatch[0], equals('oo '));
+      expect(scanner.position, equals(4));
+      expect(scanner.rest, equals('bar'));
+    });
+
+    test('throws an ArgumentError if the position is -1', () {
+      expect(() => new StringScanner('foo bar', position: -1),
+          throwsArgumentError);
+    });
+
+    test('throws an ArgumentError if the position is beyond the string', () {
+      expect(() => new StringScanner('foo bar', position: 8),
+          throwsArgumentError);
+    });
+  });
+}