diff --git a/baseline/bin/baseline.dart b/baseline/bin/baseline.dart
index bc549fc..607689f 100755
--- a/baseline/bin/baseline.dart
+++ b/baseline/bin/baseline.dart
@@ -7,5 +7,5 @@
 import 'package:baseline/options.dart';
 
 void main(List<String> arguments) async {
-  await baseline(BaselineOptions(arguments));
+  await baseline(BaselineOptions.parse(arguments));
 }
diff --git a/baseline/lib/baseline.dart b/baseline/lib/baseline.dart
index b68bfd7..fd8653b 100644
--- a/baseline/lib/baseline.dart
+++ b/baseline/lib/baseline.dart
@@ -17,6 +17,8 @@
   await Future.wait([
     for (final channel in options.channels)
       if (channel == 'main')
+        // baseline a new builder on main
+        // builder,builder2 -> new-builder
         baselineBuilder(
             options.builders,
             channel,
@@ -24,9 +26,23 @@
             options.target,
             options.configs,
             options.dryRun,
-            options.ignoreUnmapped,
+            options.mapping,
+            resultBase)
+      else if (options.builders.contains(options.target))
+        // baseline a builder on a channel with main builder data
+        // builder,builder2 -> builder-dev
+        baselineBuilder(
+            options.builders,
+            channel,
+            options.suites,
+            '${options.target}-$channel',
+            options.configs,
+            options.dryRun,
+            options.mapping,
             resultBase)
       else
+        // baseline a builder on a channel with channel builder data
+        // builder-dev,builder2-dev -> new-builder-dev
         baselineBuilder(
             options.builders.map((b) => '$b-$channel').toList(),
             channel,
@@ -34,7 +50,7 @@
             '${options.target}-$channel',
             options.configs,
             options.dryRun,
-            options.ignoreUnmapped,
+            options.mapping,
             resultBase)
   ]);
 }
@@ -46,7 +62,7 @@
     String target,
     Map<String, String> configs,
     bool dryRun,
-    bool ignoreUnmapped,
+    ConfigurationMapping mapping,
     String resultBase) async {
   var resultsStream = Pool(4).forEach(builders, (builder) async {
     var latest = await read('$resultBase/builders/$builder/latest');
@@ -55,14 +71,12 @@
   var modifiedResults = StringBuffer();
   var modifiedResultsPerConfig = <String, StringBuffer>{};
   await for (var results in resultsStream) {
-    for (var json in LineSplitter.split(results).map(jsonDecode)) {
-      var configuration = configs[json['configuration']];
+    for (var json in LineSplitter.split(results)
+        .map(jsonDecode)
+        .cast<Map<String, dynamic>>()) {
+      var configuration = mapping(json['configuration'], configs);
       if (configuration == null) {
-        if (ignoreUnmapped) {
-          continue;
-        }
-        throw Exception(
-            "Missing configuration mapping for ${json['configuration']}");
+        continue;
       }
       if (suites.isNotEmpty && !suites.contains(json['suite'])) continue;
       json['configuration'] = configuration;
diff --git a/baseline/lib/options.dart b/baseline/lib/options.dart
index df8ed0f..d4aea52 100644
--- a/baseline/lib/options.dart
+++ b/baseline/lib/options.dart
@@ -7,15 +7,18 @@
 import 'package:args/args.dart';
 
 class BaselineOptions {
-  late final bool ignoreUnmapped;
-  late final bool dryRun;
-  late final List<String> builders;
-  late final Map<String, String> configs;
-  late final List<String> channels;
-  late final Set<String> suites;
-  late final String target;
+  final List<String> builders;
+  final Map<String, String> configs;
+  final bool dryRun;
+  final List<String> channels;
+  final ConfigurationMapping mapping;
+  final Set<String> suites;
+  final String target;
 
-  BaselineOptions(List<String> arguments) {
+  BaselineOptions(this.builders, this.configs, this.dryRun, this.channels,
+      this.mapping, this.suites, this.target);
+
+  factory BaselineOptions.parse(List<String> arguments) {
     var parser = ArgParser();
     parser.addMultiOption('channel',
         abbr: 'c',
@@ -24,6 +27,7 @@
         help: 'a comma separated list of channels');
     parser.addMultiOption('config-mapping',
         abbr: 'm',
+        defaultsTo: ['*'],
         help: 'a comma separated list of configuration mappings in the form:'
             '<old1>:<new1>,<old2>:<new2>');
     parser.addMultiOption('builders',
@@ -43,7 +47,6 @@
         defaultsTo: false,
         help: 'ignore tests in unmapped configurations',
         negatable: false);
-
     parser.addFlag('help',
         abbr: 'h', negatable: false, help: 'prints this message');
     var parsed = parser.parse(arguments);
@@ -53,16 +56,49 @@
       print(parser.usage);
       exit(64);
     }
-    builders = (parsed['builders'] as List<String>);
-    configs = {
-      for (var v in ((parsed['config-mapping'] as Iterable<String>)
-          .map((c) => c.split(':'))))
-        v[0]: v[1]
-    };
-    ignoreUnmapped = parsed['ignore-unmapped'];
-    dryRun = parsed['dry-run'];
-    channels = parsed['channel'];
-    suites = Set.unmodifiable(parsed['suites']);
-    target = parsed['target'];
+    var builders = (parsed['builders'] as List<String>);
+    final target = parsed['target'];
+    if (builders.isEmpty) {
+      builders = [target];
+    }
+    var mapping = parsed['ignore-unmapped']
+        ? ConfigurationMapping.relaxed
+        : ConfigurationMapping.strict;
+    var configs = const <String, String>{};
+    final configMapping = parsed['config-mapping'] as List<String>;
+    if (configMapping.length == 1 && configMapping.first == '*') {
+      mapping = ConfigurationMapping.none;
+    } else {
+      configs = {
+        for (var v in configMapping.map((c) => c.split(':'))) v[0]: v[1]
+      };
+    }
+    final dryRun = parsed['dry-run'];
+    final channels = parsed['channel'];
+    final suites = Set.unmodifiable(parsed['suites'] as List<String>);
+
+    return BaselineOptions(
+        builders, configs, dryRun, channels, mapping, suites, target);
   }
 }
+
+String? _strict(String configuration, Map<String, String> configs) =>
+    configs[configuration] ??
+    (throw Exception("Missing configuration mapping for $configuration"));
+String? _relaxed(String configuration, Map<String, String> configs) =>
+    configs[configuration];
+String? _none(String configuration, Map<String, String> configs) =>
+    configuration;
+
+enum ConfigurationMapping {
+  none(_none),
+  strict(_strict),
+  relaxed(_relaxed);
+
+  const ConfigurationMapping(this.mapping);
+  final String? Function(String configuration, Map<String, String> configs)
+      mapping;
+
+  String? call(String configuration, Map<String, String> configs) =>
+      mapping(configuration, configs);
+}
diff --git a/baseline/test/baseline_test.dart b/baseline/test/baseline_test.dart
index 0694b5c..aca7363 100644
--- a/baseline/test/baseline_test.dart
+++ b/baseline/test/baseline_test.dart
@@ -56,7 +56,7 @@
   test('baseline missing config mapping throws', () {
     expect(
         baseline(
-            BaselineOptions([
+            BaselineOptions.parse([
               '--builders=builder,builder2',
               '--target=new-builder',
               '--channel=main,stable',
@@ -103,6 +103,50 @@
     });
   });
 
+  test('baseline default config mapping', () async {
+    final newBuilderDevResults = [
+      '{"build_number":"0","previous_build_number":"0","builder_name":"builder-dev","configuration":"config1","suite":"suite1","test_name":"test1","result":"FAIL","flaky":false,"previous_flaky":false}',
+      '{"build_number":"0","previous_build_number":"0","builder_name":"builder-dev","configuration":"config2","suite":"suite2","test_name":"test2","result":"PASS","flaky":false,"previous_flaky":false}',
+      '{"build_number":"0","previous_build_number":"0","builder_name":"builder-dev","configuration":"config3","suite":"suite1","test_name":"test1","result":"FAIL","flaky":false,"previous_flaky":false}',
+      '{"build_number":"0","previous_build_number":"0","builder_name":"builder-dev","configuration":"config4","suite":"suite2","test_name":"test2","result":"PASS","flaky":false,"previous_flaky":false}',
+    ];
+    final newBuilderStableResults = [
+      '{"build_number":"0","previous_build_number":"0","builder_name":"builder-stable","configuration":"config1","suite":"suite1","test_name":"test1","result":"FAIL","flaky":false,"previous_flaky":false}',
+      '{"build_number":"0","previous_build_number":"0","builder_name":"builder-stable","configuration":"config2","suite":"suite2","test_name":"test2","result":"PASS","flaky":false,"previous_flaky":false}',
+      '{"build_number":"0","previous_build_number":"0","builder_name":"builder-stable","configuration":"config3","suite":"suite1","test_name":"test1","result":"FAIL","flaky":false,"previous_flaky":false}',
+      '{"build_number":"0","previous_build_number":"0","builder_name":"builder-stable","configuration":"config4","suite":"suite2","test_name":"test2","result":"PASS","flaky":false,"previous_flaky":false}',
+    ];
+    await baselineTest([
+      '--builders=builder,builder2',
+      '--target=builder',
+      '--channel=dev,stable',
+    ], {
+      ...testData,
+      'builders/builder-stable/0/results.json':
+          unorderedEquals(newBuilderStableResults),
+      'builders/builder-stable/latest': ['0'],
+      'configuration/stable/config1/0/results.json': [
+        newBuilderStableResults[0]
+      ],
+      'configuration/stable/config2/0/results.json': [
+        newBuilderStableResults[1]
+      ],
+      'configuration/stable/config3/0/results.json': [
+        newBuilderStableResults[2]
+      ],
+      'configuration/stable/config4/0/results.json': [
+        newBuilderStableResults[3]
+      ],
+      'builders/builder-dev/0/results.json':
+          unorderedEquals(newBuilderDevResults),
+      'builders/builder-dev/latest': ['0'],
+      'configuration/dev/config1/0/results.json': [newBuilderDevResults[0]],
+      'configuration/dev/config2/0/results.json': [newBuilderDevResults[1]],
+      'configuration/dev/config3/0/results.json': [newBuilderDevResults[2]],
+      'configuration/dev/config4/0/results.json': [newBuilderDevResults[3]],
+    });
+  });
+
   test('baseline dry-run', () async {
     await baselineTest([
       '--builders=builder,builder2',
@@ -200,7 +244,7 @@
   var temp = await Directory.systemTemp.createTemp();
   try {
     await copyPath('test/data', temp.path);
-    await baseline(BaselineOptions(arguments), temp.path);
+    await baseline(BaselineOptions.parse(arguments), temp.path);
     var files = temp
         .listSync(recursive: true)
         .whereType<File>()
diff --git a/baseline/test/options_test.dart b/baseline/test/options_test.dart
index 856758e..ed9d9c1 100644
--- a/baseline/test/options_test.dart
+++ b/baseline/test/options_test.dart
@@ -15,39 +15,67 @@
   ]) {
     var arguments = ['-c${channels.join(',')}', ..._builders];
     test('channels: "$arguments"', () {
-      var options = BaselineOptions(arguments);
+      var options = BaselineOptions.parse(arguments);
       expect(options.channels, channels);
     });
   }
 
   test('builder-mapping', () {
-    var options = BaselineOptions(_builders);
+    var options = BaselineOptions.parse(_builders);
     expect(options.builders, ['a1', 'a2']);
     expect(options.target, 'b');
   });
 
+  test('builder-mapping: default to target', () {
+    var options = BaselineOptions.parse(['-tb']);
+    expect(options.builders, ['b']);
+  });
+
   test('config-mapping', () {
-    var options = BaselineOptions(['-mc:d,e:f', ..._builders]);
+    var options = BaselineOptions.parse(['-mc:d,e:f', ..._builders]);
     expect(options.configs, {'c': 'd', 'e': 'f'});
+    expect(options.mapping, ConfigurationMapping.strict);
+  });
+
+  test('config-mapping: star', () {
+    var options = BaselineOptions.parse(['-m*', ..._builders]);
+    expect(options.configs, const {});
+    expect(options.mapping, ConfigurationMapping.none);
+  });
+
+  test('config-mapping: ignore-unmapped', () {
+    var options = BaselineOptions.parse(['-u', '-mc:d,e:f', ..._builders]);
+    expect(options.mapping, ConfigurationMapping.relaxed);
   });
 
   test('suites', () {
-    var options = BaselineOptions(['-ss1,s2', ..._builders]);
+    var options = BaselineOptions.parse(['-ss1,s2', ..._builders]);
     expect(options.suites, {'s1', 's2'});
   });
 
-  test('ignore-unmapped', () {
-    var options = BaselineOptions(['-u', '-mc:d,e:f', ..._builders]);
-    expect(options.ignoreUnmapped, true);
-  });
-
   test('dry-run defaults to false', () {
-    var options = BaselineOptions(_builders);
+    var options = BaselineOptions.parse(_builders);
     expect(options.dryRun, false);
   });
 
   test('dry-run: true', () {
-    var options = BaselineOptions(['-n', ..._builders]);
+    var options = BaselineOptions.parse(['-n', ..._builders]);
     expect(options.dryRun, true);
   });
+
+  test('mapping: strict', () {
+    expect(ConfigurationMapping.strict('foo', {'foo': 'bar'}), 'bar');
+    expect(() => ConfigurationMapping.strict('oof', {'foo': 'bar'}),
+        throwsException);
+  });
+
+  test('mapping: relaxed', () {
+    expect(ConfigurationMapping.relaxed('foo', {'foo': 'bar'}), 'bar');
+    expect(ConfigurationMapping.relaxed('oof', {'foo': 'bar'}), null);
+  });
+
+  test('mapping: none', () {
+    expect(ConfigurationMapping.none('foo', {'foo': 'bar'}), 'foo');
+    expect(ConfigurationMapping.none('oof', {'foo': 'bar'}), 'oof');
+  });
 }