diff --git a/.gitignore b/.gitignore
index 00eaddbb..8160f445 100644
--- a/.gitignore
+++ b/.gitignore
@@ -28,4 +28,5 @@ pubspec.lock
 
 log.txt
 
-.idea
\ No newline at end of file
+.idea
+.dart_tool
\ No newline at end of file
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4566b79b..109c3eeb 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,6 @@
+# 1.0.5
+* Use `wrapMatcher` on explicit values instead of throwing.
+
 # 1.0.4
 * `isNonEmptyString` trims strings.
 * `ValidationException` extends `AngelHttpException`.
diff --git a/lib/server.dart b/lib/server.dart
index fa983fc7..b4e5d18d 100644
--- a/lib/server.dart
+++ b/lib/server.dart
@@ -2,7 +2,9 @@
 library angel_validate.server;
 
 import 'package:angel_framework/angel_framework.dart';
+import 'src/async.dart';
 import 'angel_validate.dart';
+export 'src/async.dart';
 export 'angel_validate.dart';
 
 /// Auto-parses numbers in `req.body`.
diff --git a/lib/src/async.dart b/lib/src/async.dart
new file mode 100644
index 00000000..538dd22e
--- /dev/null
+++ b/lib/src/async.dart
@@ -0,0 +1,131 @@
+import 'dart:async';
+import 'package:angel_framework/angel_framework.dart';
+import 'package:angel_http_exception/angel_http_exception.dart';
+import 'package:matcher/matcher.dart';
+
+/// Returns an [AngelMatcher] that uses an arbitrary function that returns
+/// true or false for the actual value.
+///
+/// Analogous to the synchronous [predicate] matcher.
+///
+/// For example:
+///
+///     expect(v, predicate((x) => ((x % 2) == 0), "is even"))
+AngelMatcher predicateWithAngel(FutureOr<bool> Function(Object, Angel) f,
+        [String description = 'satisfies function']) =>
+    new _PredicateWithAngel(f, description);
+
+/// Returns an [AngelMatcher] that applies an asynchronously-created [Matcher]
+/// to the input.
+///
+/// Use this to match values against configuration, injections, etc.
+AngelMatcher matchWithAngel(FutureOr<Matcher> Function(Object, Angel) f,
+        [String description = 'satisfies asynchronously created matcher']) =>
+    new _MatchWithAngel(f, description);
+
+/// Calls [matchWithAngel] without the initial parameter.
+AngelMatcher matchWithAngelUnary(FutureOr<Matcher> Function(Angel) f,
+        [String description = 'satisfies asynchronously created matcher']) =>
+    matchWithAngel((_, app) => f(app));
+
+/// Returns an [AngelMatcher] that represents [x].
+///
+/// If [x] is an [AngelMatcher], then it is returned, unmodified.
+AngelMatcher wrapAngelMatcher(x) {
+  if (x is AngelMatcher) return x;
+  return matchWithAngel((_, app) => wrapMatcher(x));
+}
+
+/// Returns an [AngelMatcher] that asynchronously resolves a [feature], builds a [matcher], and executes it.
+AngelMatcher matchAsync(
+    FutureOr<Matcher> Function(Object) matcher, FutureOr Function() feature,
+    [String description = 'satisfies asynchronously created matcher']) {
+  return new _MatchAsync(matcher, feature, description);
+}
+
+/// Returns an [AngelMatcher] that verifies that an item with the given [idField]
+/// exists in the service at [servicePath], without throwing a `404` or returning `null`.
+AngelMatcher idExistsInService(String servicePath,
+    {String idField: 'id', String description}) {
+  return predicateWithAngel(
+    (item, app) async {
+      try {
+        var result = await app.service(servicePath)?.read(item);
+        return result != null;
+      } on AngelHttpException catch (e) {
+        if (e.statusCode == 404) {
+          return false;
+        } else {
+          rethrow;
+        }
+      }
+    },
+    description ?? 'exists in service $servicePath',
+  );
+}
+
+/// An asynchronous [Matcher] that runs in the context of an [Angel] app.
+abstract class AngelMatcher extends Matcher {
+  Future<bool> matchesAsync(item, Map matchState, Angel app);
+
+  @override
+  bool matches(item, Map matchState) {
+    return true;
+  }
+}
+
+class _MatchWithAngel extends AngelMatcher {
+  final FutureOr<Matcher> Function(Object, Angel) f;
+  final String description;
+
+  _MatchWithAngel(this.f, this.description);
+
+  @override
+  Description describe(Description description) => this.description == null
+      ? description
+      : description.add(this.description);
+
+  @override
+  Future<bool> matchesAsync(item, Map matchState, Angel app) {
+    return new Future.sync(() => f(item, app)).then((result) {
+      return result.matches(item, matchState);
+    });
+  }
+}
+
+class _PredicateWithAngel extends AngelMatcher {
+  final FutureOr<bool> Function(Object, Angel) predicate;
+  final String description;
+
+  _PredicateWithAngel(this.predicate, this.description);
+
+  @override
+  Description describe(Description description) => this.description == null
+      ? description
+      : description.add(this.description);
+
+  @override
+  Future<bool> matchesAsync(item, Map matchState, Angel app) {
+    return new Future<bool>.sync(() => predicate(item, app));
+  }
+}
+
+class _MatchAsync extends AngelMatcher {
+  final FutureOr<Matcher> Function(Object) matcher;
+  final FutureOr Function() feature;
+  final String description;
+
+  _MatchAsync(this.matcher, this.feature, this.description);
+
+  @override
+  Description describe(Description description) => this.description == null
+      ? description
+      : description.add(this.description);
+
+  @override
+  Future<bool> matchesAsync(item, Map matchState, Angel app) async {
+    var f = await feature();
+    var m = await matcher(f);
+    return m.matches(item, matchState);
+  }
+}
diff --git a/lib/src/validator.dart b/lib/src/validator.dart
index 9ae82a0e..fea5eac4 100644
--- a/lib/src/validator.dart
+++ b/lib/src/validator.dart
@@ -96,8 +96,7 @@ class Validator extends Matcher {
           } else if (rule is Filter) {
             addRule(fieldName, predicate(rule));
           } else {
-            throw new ArgumentError(
-                'Cannot use a(n) ${rule.runtimeType} as a validation rule.');
+            addRule(fieldName, wrapMatcher(rule));
           }
         }
       }