diff --git a/lib/src/command.dart b/lib/src/command.dart
index e86dd50..4a65fb1 100644
--- a/lib/src/command.dart
+++ b/lib/src/command.dart
@@ -194,7 +194,6 @@
       return exit_codes.SUCCESS;
     } catch (error, chain) {
       log.exception(error, chain);
-
       if (_pubTopLevel.trace) {
         log.dumpTranscriptToStdErr();
       } else if (!isUserFacingException(error)) {
diff --git a/lib/src/entrypoint.dart b/lib/src/entrypoint.dart
index b536cca..36f8047 100644
--- a/lib/src/entrypoint.dart
+++ b/lib/src/entrypoint.dart
@@ -12,6 +12,7 @@
 import 'package:path/path.dart' as p;
 import 'package:pool/pool.dart';
 import 'package:pub_semver/pub_semver.dart';
+import 'package:source_span/source_span.dart';
 import 'package:yaml/yaml.dart';
 
 import 'command_runner.dart';
@@ -101,7 +102,17 @@
     if (!fileExists(lockFilePath)) {
       return _lockFile = LockFile.empty();
     } else {
-      return _lockFile = LockFile.load(lockFilePath, cache.sources);
+      try {
+        return _lockFile = LockFile.load(lockFilePath, cache.sources);
+      } on SourceSpanException catch (e) {
+        throw SourceSpanApplicationException(
+          e.message,
+          e.span,
+          explanation: 'Failed parsing lock file:',
+          hint:
+              'Consider deleting the file and running `$topLevelProgram pub get` to recreate it.',
+        );
+      }
     }
   }
 
@@ -898,7 +909,7 @@
         final keyNode = environment.nodes.entries
             .firstWhere((e) => (e.key as YamlNode).value == sdk)
             .key as YamlNode;
-        throw PubspecException('''
+        throw SourceSpanApplicationException('''
 $pubspecPath refers to an unknown sdk '$sdk'.
 
 Did you mean to add it as a dependency?
diff --git a/lib/src/exceptions.dart b/lib/src/exceptions.dart
index ec9f876..39e9c51 100644
--- a/lib/src/exceptions.dart
+++ b/lib/src/exceptions.dart
@@ -7,6 +7,7 @@
 
 import 'package:args/command_runner.dart';
 import 'package:http/http.dart' as http;
+import 'package:source_span/source_span.dart';
 import 'package:stack_trace/stack_trace.dart';
 import 'package:yaml/yaml.dart';
 
@@ -127,3 +128,34 @@
       error is YamlException ||
       error is UsageException;
 }
+
+/// An exception thrown when parsing a `pubspec.yaml` or a `pubspec.lock`.
+///
+/// These exceptions are often thrown lazily while accessing pubspec properties.
+///
+/// By being an [ApplicationException] this will not trigger a stack-trace on
+/// normal operations.
+///
+/// Works as a [SourceSpanFormatException], but can contain more context:
+/// An optional [explanation] that explains the operation that failed.
+/// An optional [hint] that gives suggestions how to proceed.
+class SourceSpanApplicationException extends SourceSpanFormatException
+    implements ApplicationException {
+  final String? explanation;
+  final String? hint;
+
+  SourceSpanApplicationException(String message, SourceSpan? span,
+      {this.hint, this.explanation})
+      : super(message, span);
+
+  @override
+  String toString({color}) {
+    return [
+      if (explanation != null) explanation,
+      span == null
+          ? message
+          : 'Error on ${span?.message(message, color: color)}',
+      if (hint != null) hint,
+    ].join('\n\n');
+  }
+}
diff --git a/lib/src/lock_file.dart b/lib/src/lock_file.dart
index 46be2bf..f133172 100644
--- a/lib/src/lock_file.dart
+++ b/lib/src/lock_file.dart
@@ -98,50 +98,54 @@
 
     Uri? sourceUrl;
     if (filePath != null) sourceUrl = p.toUri(filePath);
-    var parsed = loadYamlNode(contents, sourceUrl: sourceUrl);
+    final parsed = _parseNode<YamlMap>(
+      loadYamlNode(contents, sourceUrl: sourceUrl),
+      'YAML mapping',
+    );
 
-    _validate(parsed is Map, 'The lockfile must be a YAML mapping.', parsed);
-    var parsedMap = parsed as YamlMap;
-
-    var sdkConstraints = <String, VersionConstraint>{};
-    var sdkNode = parsedMap.nodes['sdk'];
+    final sdkConstraints = <String, VersionConstraint>{};
+    final sdkNode =
+        _getEntry<YamlScalar?>(parsed, 'sdk', 'string', required: false);
     if (sdkNode != null) {
       // Lockfiles produced by pub versions from 1.14.0 through 1.18.0 included
       // a top-level "sdk" field which encoded the unified constraint on the
       // Dart SDK. They had no way of specifying constraints on other SDKs.
       sdkConstraints['dart'] = _parseVersionConstraint(sdkNode);
-    } else if (parsedMap.containsKey('sdks')) {
-      var sdksField = parsedMap['sdks'];
-      _validate(sdksField is Map, 'The "sdks" field must be a mapping.',
-          parsedMap.nodes['sdks']);
-
-      sdksField.nodes.forEach((name, constraint) {
-        _validate(name.value is String, 'SDK names must be strings.', name);
-        sdkConstraints[name.value as String] =
-            _parseVersionConstraint(constraint);
-      });
     }
 
-    var packages = <String, PackageId>{};
-    var packageEntries = parsedMap['packages'];
-    if (packageEntries != null) {
-      _validate(packageEntries is Map, 'The "packages" field must be a map.',
-          parsedMap.nodes['packages']);
+    final sdksField =
+        _getEntry<YamlMap?>(parsed, 'sdks', 'map', required: false);
 
-      packageEntries.forEach((name, spec) {
+    if (sdksField != null) {
+      _parseEachEntry<String, YamlScalar>(sdksField, (name, constraint) {
+        sdkConstraints[name] = _parseVersionConstraint(constraint);
+      }, 'string', 'string');
+    }
+
+    final packages = <String, PackageId>{};
+
+    final mainDependencies = <String>{};
+    final devDependencies = <String>{};
+    final overriddenDependencies = <String>{};
+
+    final packageEntries =
+        _getEntry<YamlMap?>(parsed, 'packages', 'map', required: false);
+
+    if (packageEntries != null) {
+      _parseEachEntry<String, YamlMap>(packageEntries, (name, spec) {
         // Parse the version.
-        _validate(spec.containsKey('version'),
-            'Package $name is missing a version.', spec);
-        var version = Version.parse(spec['version']);
+        final versionEntry = _getStringEntry(spec, 'version');
+        final version = Version.parse(versionEntry);
 
         // Parse the source.
-        _validate(spec.containsKey('source'),
-            'Package $name is missing a source.', spec);
-        var sourceName = spec['source'];
+        final sourceName = _getStringEntry(spec, 'source');
 
-        _validate(spec.containsKey('description'),
-            'Package $name is missing a description.', spec);
-        var description = spec['description'];
+        var descriptionNode =
+            _getEntry<YamlNode>(spec, 'description', 'description');
+
+        dynamic description = descriptionNode is YamlScalar
+            ? descriptionNode.value
+            : descriptionNode;
 
         // Let the source parse the description.
         var source = sources(sourceName);
@@ -150,18 +154,30 @@
           id = source.parseId(name, version, description,
               containingDir: filePath == null ? null : p.dirname(filePath));
         } on FormatException catch (ex) {
-          throw SourceSpanFormatException(
-              ex.message, spec.nodes['description'].span);
+          _failAt(ex.message, spec.nodes['description']!);
         }
 
         // Validate the name.
-        _validate(name == id.name,
-            "Package name $name doesn't match ${id.name}.", spec);
+        if (name != id.name) {
+          _failAt("Package name $name doesn't match ${id.name}.", spec);
+        }
 
         packages[name] = id;
-      });
+        if (spec.containsKey('dependency')) {
+          final dependencyKind = _getStringEntry(spec, 'dependency');
+          switch (dependencyKind) {
+            case _directMain:
+              mainDependencies.add(name);
+              break;
+            case _directDev:
+              devDependencies.add(name);
+              break;
+            case _directOverridden:
+              overriddenDependencies.add(name);
+          }
+        }
+      }, 'string', 'map');
     }
-
     return LockFile._(
         packages,
         sdkConstraints,
@@ -170,15 +186,6 @@
         const UnmodifiableSetView.empty());
   }
 
-  /// Asserts that [node] is a version constraint, and parses it.
-  static VersionConstraint _parseVersionConstraint(YamlNode node) {
-    _validate(node.value is String,
-        'Invalid version constraint: must be a string.', node);
-
-    return _wrapFormatException('version constraint', node.span,
-        () => VersionConstraint.parse(node.value));
-  }
-
   /// Runs [fn] and wraps any [FormatException] it throws in a
   /// [SourceSpanFormatException].
   ///
@@ -195,10 +202,68 @@
     }
   }
 
-  /// If [condition] is `false` throws a format error with [message] for [node].
-  static void _validate(bool condition, String message, YamlNode? node) {
-    if (condition) return;
-    throw SourceSpanFormatException(message, node!.span);
+  static VersionConstraint _parseVersionConstraint(YamlNode node) {
+    return _parseNode(node, 'version constraint',
+        parse: VersionConstraint.parse);
+  }
+
+  static String _getStringEntry(YamlMap map, String key) {
+    return _parseNode<String>(
+        _getEntry<YamlScalar>(map, key, 'string'), 'string');
+  }
+
+  static T _parseNode<T>(YamlNode node, String typeDescription,
+      {T Function(String)? parse}) {
+    if (node is T) {
+      return node as T;
+    } else if (node is YamlScalar) {
+      final value = node.value;
+      if (parse != null) {
+        if (value is! String) {
+          _failAt('Expected a $typeDescription.', node);
+        }
+        return _wrapFormatException(
+            'Expected a $typeDescription.', node.span, () => parse(node.value));
+      } else if (value is T) {
+        return value;
+      }
+      _failAt('Expected a $typeDescription.', node);
+    }
+    _failAt('Expected a $typeDescription.', node);
+  }
+
+  static void _parseEachEntry<K, V>(
+      YamlMap map,
+      void Function(K key, V value) f,
+      String keyTypeDescription,
+      String valueTypeDescription) {
+    map.nodes.forEach((key, value) {
+      f(_parseNode(key, keyTypeDescription),
+          _parseNode(value, valueTypeDescription));
+    });
+  }
+
+  static T _getEntry<T>(
+    YamlMap map,
+    String key,
+    String type, {
+    bool required = true,
+  }) {
+    final entry = map.nodes[key];
+    // `null` here always means not present. A value explicitly mapped to `null`
+    // would be a `YamlScalar(null)`.
+    if (entry == null) {
+      if (required) {
+        _failAt('Expected a `$key` entry.', map);
+      } else {
+        return null as T;
+      }
+    }
+    return _parseNode(entry, type);
+  }
+
+  static Never _failAt(String message, YamlNode node) {
+    throw SourceSpanFormatException(message, node.span);
   }
 
   /// Returns a copy of this LockFile with a package named [name] removed.
@@ -304,17 +369,22 @@
 ''';
   }
 
+  static const _directMain = 'direct main';
+  static const _directDev = 'direct dev';
+  static const _directOverridden = 'direct overridden';
+  static const _transitive = 'transitive';
+
   /// Returns the dependency classification for [package].
   String _dependencyType(String package) {
-    if (_mainDependencies.contains(package)) return 'direct main';
-    if (_devDependencies.contains(package)) return 'direct dev';
+    if (_mainDependencies.contains(package)) return _directMain;
+    if (_devDependencies.contains(package)) return _directDev;
 
     // If a package appears in `dependency_overrides` and another dependency
     // section, the main section it appears in takes precedence.
     if (_overriddenDependencies.contains(package)) {
-      return 'direct overridden';
+      return _directOverridden;
     }
-    return 'transitive';
+    return _transitive;
   }
 
   /// `true` if [other] has the same packages as `this` in the same versions
diff --git a/lib/src/pubspec.dart b/lib/src/pubspec.dart
index 0b6cd5b..6e1d566 100644
--- a/lib/src/pubspec.dart
+++ b/lib/src/pubspec.dart
@@ -133,7 +133,7 @@
     if (pubspecOverridesFields != null) {
       pubspecOverridesFields.nodes.forEach((key, _) {
         if (!const {'dependency_overrides'}.contains(key.value)) {
-          throw PubspecException(
+          throw SourceSpanApplicationException(
             'pubspec_overrides.yaml only supports the `dependency_overrides` field.',
             key.span,
           );
@@ -293,7 +293,7 @@
   /// Loads the pubspec for a package located in [packageDir].
   ///
   /// If [expectedName] is passed and the pubspec doesn't have a matching name
-  /// field, this will throw a [PubspecException].
+  /// field, this will throw a [SourceSpanApplicationException].
   ///
   /// If [allowOverridesFile] is `true` [pubspecOverridesFilename] is loaded and
   /// is allowed to override dependency_overrides from `pubspec.yaml`.
@@ -373,7 +373,7 @@
     if (expectedName == null) return;
     if (name == expectedName) return;
 
-    throw PubspecException(
+    throw SourceSpanApplicationException(
         '"name" field doesn\'t match expected name '
         '"$expectedName".',
         this.fields.nodes['name']!.span);
@@ -400,7 +400,7 @@
             loadYamlNode(overridesFileContents, sourceUrl: overridesLocation));
       }
     } on YamlException catch (error) {
-      throw PubspecException(error.message, error.span);
+      throw SourceSpanApplicationException(error.message, error.span);
     }
 
     return Pubspec.fromMap(pubspecMap, sources,
@@ -420,19 +420,20 @@
     } else if (node is YamlMap) {
       return node;
     } else {
-      throw PubspecException('The pubspec must be a YAML mapping.', node.span);
+      throw SourceSpanApplicationException(
+          'The pubspec must be a YAML mapping.', node.span);
     }
   }
 
   /// Returns a list of most errors in this pubspec.
   ///
   /// This will return at most one error for each field.
-  List<PubspecException> get allErrors {
-    var errors = <PubspecException>[];
+  List<SourceSpanApplicationException> get allErrors {
+    var errors = <SourceSpanApplicationException>[];
     void collectError(void Function() fn) {
       try {
         fn();
-      } on PubspecException catch (e) {
+      } on SourceSpanApplicationException catch (e) {
         errors.add(e);
       }
     }
@@ -591,7 +592,7 @@
 }
 
 /// Runs [fn] and wraps any [FormatException] it throws in a
-/// [PubspecException].
+/// [SourceSpanApplicationException].
 ///
 /// [description] should be a noun phrase that describes whatever's being
 /// parsed or processed by [fn]. [span] should be the location of whatever's
@@ -611,7 +612,7 @@
     return fn();
   } on FormatException catch (e) {
     // If we already have a pub exception with a span, re-use that
-    if (e is PubspecException) rethrow;
+    if (e is SourceSpanApplicationException) rethrow;
 
     var msg = 'Invalid $description';
     final typeName = _fileTypeName(fileType);
@@ -624,9 +625,9 @@
   }
 }
 
-/// Throws a [PubspecException] with the given message.
+/// Throws a [SourceSpanApplicationException] with the given message.
 Never _error(String message, SourceSpan? span) {
-  throw PubspecException(message, span);
+  throw SourceSpanApplicationException(message, span);
 }
 
 enum _FileType {
diff --git a/lib/src/pubspec_parse.dart b/lib/src/pubspec_parse.dart
index c86a706..c6babfb 100644
--- a/lib/src/pubspec_parse.dart
+++ b/lib/src/pubspec_parse.dart
@@ -7,7 +7,7 @@
 import 'package:source_span/source_span.dart';
 import 'package:yaml/yaml.dart';
 
-import 'exceptions.dart' show ApplicationException;
+import 'exceptions.dart';
 import 'utils.dart' show identifierRegExp, reservedWords;
 
 /// A regular expression matching allowed package names.
@@ -42,15 +42,18 @@
   String _lookupName() {
     final name = fields['name'];
     if (name == null) {
-      throw PubspecException('Missing the required "name" field.', fields.span);
+      throw SourceSpanApplicationException(
+          'Missing the required "name" field.', fields.span);
     } else if (name is! String) {
-      throw PubspecException(
+      throw SourceSpanApplicationException(
           '"name" field must be a string.', fields.nodes['name']?.span);
     } else if (!packageNameRegExp.hasMatch(name)) {
-      throw PubspecException('"name" field must be a valid Dart identifier.',
+      throw SourceSpanApplicationException(
+          '"name" field must be a valid Dart identifier.',
           fields.nodes['name']?.span);
     } else if (reservedWords.contains(name)) {
-      throw PubspecException('"name" field may not be a Dart reserved word.',
+      throw SourceSpanApplicationException(
+          '"name" field may not be a Dart reserved word.',
           fields.nodes['name']?.span);
     }
 
@@ -223,7 +226,7 @@
   bool get isPrivate => publishTo == 'none';
 
   /// Runs [fn] and wraps any [FormatException] it throws in a
-  /// [PubspecException].
+  /// [SourceSpanApplicationException].
   ///
   /// [description] should be a noun phrase that describes whatever's being
   /// parsed or processed by [fn]. [span] should be the location of whatever's
@@ -242,21 +245,13 @@
         msg = '$msg in the "$name" pubspec on the "$targetPackage" dependency';
       }
       msg = '$msg: ${e.message}';
-      throw PubspecException(msg, span);
+      throw SourceSpanApplicationException(msg, span);
     }
   }
 
-  /// Throws a [PubspecException] with the given message.
+  /// Throws a [SourceSpanApplicationException] with the given message.
   @alwaysThrows
   void _error(String message, SourceSpan? span) {
-    throw PubspecException(message, span);
+    throw SourceSpanApplicationException(message, span);
   }
 }
-
-/// An exception thrown when parsing a pubspec.
-///
-/// These exceptions are often thrown lazily while accessing pubspec properties.
-class PubspecException extends SourceSpanFormatException
-    implements ApplicationException {
-  PubspecException(String message, SourceSpan? span) : super(message, span);
-}
diff --git a/lib/src/solver/package_lister.dart b/lib/src/solver/package_lister.dart
index ce2b4c1..1597e73 100644
--- a/lib/src/solver/package_lister.dart
+++ b/lib/src/solver/package_lister.dart
@@ -190,7 +190,7 @@
     try {
       pubspec = await withDependencyType(
           _dependencyType, () => _systemCache.describe(id));
-    } on PubspecException catch (error) {
+    } on SourceSpanApplicationException catch (error) {
       // The lockfile for the pubspec couldn't be parsed,
       log.fine('Failed to parse pubspec for $id:\n$error');
       _knownInvalidVersions = _knownInvalidVersions.union(id.version);
diff --git a/test/list_package_dirs/lockfile_error_test.dart b/test/list_package_dirs/lockfile_error_test.dart
index f4440ec..5c7bff9 100644
--- a/test/list_package_dirs/lockfile_error_test.dart
+++ b/test/list_package_dirs/lockfile_error_test.dart
@@ -19,7 +19,7 @@
       'list-package-dirs',
       '--format=json'
     ], outputJson: {
-      'error': contains('The lockfile must be a YAML mapping.'),
+      'error': contains('Expected a YAML mapping.'),
       'path': canonicalize(path.join(d.sandbox, appPath, 'pubspec.lock'))
     }, exitCode: exit_codes.DATA);
   });
diff --git a/test/pubspec_test.dart b/test/pubspec_test.dart
index 2ccb30f..1a9ac48 100644
--- a/test/pubspec_test.dart
+++ b/test/pubspec_test.dart
@@ -4,6 +4,7 @@
 
 import 'dart:io';
 
+import 'package:pub/src/exceptions.dart';
 import 'package:pub/src/pubspec.dart';
 import 'package:pub/src/sdk.dart';
 import 'package:pub/src/source/hosted.dart';
@@ -15,11 +16,12 @@
   group('parse()', () {
     final sources = SystemCache().sources;
 
-    var throwsPubspecException = throwsA(const TypeMatcher<PubspecException>());
+    var throwsPubspecException =
+        throwsA(const TypeMatcher<SourceSpanApplicationException>());
 
     void expectPubspecException(String contents, void Function(Pubspec) fn,
         [String? expectedContains]) {
-      var expectation = const TypeMatcher<PubspecException>();
+      var expectation = const TypeMatcher<SourceSpanApplicationException>();
       if (expectedContains != null) {
         expectation = expectation.having(
             (error) => error.message, 'message', contains(expectedContains));
@@ -390,7 +392,7 @@
           expect(
             () => pubspec.dependencies,
             throwsA(
-              isA<PubspecException>()
+              isA<SourceSpanApplicationException>()
                   .having((e) => e.span!.text, 'span.text', 'invalid value'),
             ),
           );
@@ -700,7 +702,7 @@
         void Function(Pubspec) fn, [
         String? expectedContains,
       ]) {
-        var expectation = isA<PubspecException>();
+        var expectation = isA<SourceSpanApplicationException>();
         if (expectedContains != null) {
           expectation = expectation.having((error) => error.toString(),
               'toString()', contains(expectedContains));