diff --git a/SabreTools.DatFiles/Formats/Listxml.Writer.cs b/SabreTools.DatFiles/Formats/Listxml.Writer.cs
index fd987665..77b18471 100644
--- a/SabreTools.DatFiles/Formats/Listxml.Writer.cs
+++ b/SabreTools.DatFiles/Formats/Listxml.Writer.cs
@@ -47,8 +47,138 @@ namespace SabreTools.DatFiles.Formats
         /// <inheritdoc/>
         protected override List<DatItemField> GetMissingRequiredFields(DatItem datItem)
         {
-            // TODO: Check required fields
-            return null;
+            var missingFields = new List<DatItemField>();
+            switch (datItem)
+            {
+                case BiosSet biosset:
+                    if (string.IsNullOrWhiteSpace(biosset.Name))
+                        missingFields.Add(DatItemField.Name);
+                    if (string.IsNullOrWhiteSpace(biosset.Description))
+                        missingFields.Add(DatItemField.Description);
+                    break;
+
+                case Rom rom:
+                    if (string.IsNullOrWhiteSpace(rom.Name))
+                        missingFields.Add(DatItemField.Name);
+                    if (rom.Size == null || rom.Size < 0)
+                        missingFields.Add(DatItemField.Size);
+                    if (string.IsNullOrWhiteSpace(rom.CRC)
+                        && string.IsNullOrWhiteSpace(rom.SHA1))
+                    {
+                        missingFields.Add(DatItemField.SHA1);
+                    }
+                    break;
+
+                case Disk disk:
+                    if (string.IsNullOrWhiteSpace(disk.Name))
+                        missingFields.Add(DatItemField.Name);
+                    if (string.IsNullOrWhiteSpace(disk.MD5)
+                        && string.IsNullOrWhiteSpace(disk.SHA1))
+                    {
+                        missingFields.Add(DatItemField.SHA1);
+                    }
+                    break;
+
+                case DeviceReference deviceref:
+                    if (string.IsNullOrWhiteSpace(deviceref.Name))
+                        missingFields.Add(DatItemField.Name);
+                    break;
+
+                case Sample sample:
+                    if (string.IsNullOrWhiteSpace(sample.Name))
+                        missingFields.Add(DatItemField.Name);
+                    break;
+
+                case Chip chip:
+                    if (string.IsNullOrWhiteSpace(chip.Name))
+                        missingFields.Add(DatItemField.Name);
+                    if (!chip.ChipTypeSpecified)
+                        missingFields.Add(DatItemField.ChipType);
+                    break;
+
+                case Display display:
+                    if (!display.DisplayTypeSpecified)
+                        missingFields.Add(DatItemField.DisplayType);
+                    if (display.Refresh == null)
+                        missingFields.Add(DatItemField.Refresh);
+                    break;
+
+                case Sound sound:
+                    if (sound.Channels == null)
+                        missingFields.Add(DatItemField.Channels);
+                    break;
+
+                case Input input:
+                    if (input.Players == null)
+                        missingFields.Add(DatItemField.Players);
+                    break;
+
+                case DipSwitch dipswitch:
+                    if (string.IsNullOrWhiteSpace(dipswitch.Name))
+                        missingFields.Add(DatItemField.Name);
+                    if (string.IsNullOrWhiteSpace(dipswitch.Tag))
+                        missingFields.Add(DatItemField.Tag);
+                    break;
+
+                case Configuration configuration:
+                    if (string.IsNullOrWhiteSpace(configuration.Name))
+                        missingFields.Add(DatItemField.Name);
+                    if (string.IsNullOrWhiteSpace(configuration.Tag))
+                        missingFields.Add(DatItemField.Tag);
+                    break;
+
+                case Port port:
+                    if (string.IsNullOrWhiteSpace(port.Tag))
+                        missingFields.Add(DatItemField.Tag);
+                    break;
+
+                case Adjuster adjuster:
+                    if (string.IsNullOrWhiteSpace(adjuster.Name))
+                        missingFields.Add(DatItemField.Name);
+                    break;
+
+                case Driver driver:
+                    if (!driver.StatusSpecified)
+                        missingFields.Add(DatItemField.SupportStatus);
+                    if (!driver.EmulationSpecified)
+                        missingFields.Add(DatItemField.EmulationStatus);
+                    if (!driver.CocktailSpecified)
+                        missingFields.Add(DatItemField.CocktailStatus);
+                    if (!driver.SaveStateSpecified)
+                        missingFields.Add(DatItemField.SaveStateStatus);
+                    break;
+
+                case Feature feature:
+                    if (!feature.TypeSpecified)
+                        missingFields.Add(DatItemField.FeatureType);
+                    break;
+
+                case Device device:
+                    if (!device.DeviceTypeSpecified)
+                        missingFields.Add(DatItemField.DeviceType);
+                    break;
+
+                case Slot slot:
+                    if (string.IsNullOrWhiteSpace(slot.Name))
+                        missingFields.Add(DatItemField.Name);
+                    break;
+
+                case DatItems.Formats.SoftwareList softwarelist:
+                    if (string.IsNullOrWhiteSpace(softwarelist.Tag))
+                        missingFields.Add(DatItemField.Tag);
+                    if (string.IsNullOrWhiteSpace(softwarelist.Name))
+                        missingFields.Add(DatItemField.Name);
+                    if (!softwarelist.StatusSpecified)
+                        missingFields.Add(DatItemField.SoftwareListStatus);
+                    break;
+
+                case RamOption ramoption:
+                    if (string.IsNullOrWhiteSpace(ramoption.Name))
+                        missingFields.Add(DatItemField.Name);
+                    break;
+            }
+
+            return missingFields;
         }
 
         /// <inheritdoc/>
diff --git a/SabreTools.Models/Listxml/Adjuster.cs b/SabreTools.Models/Listxml/Adjuster.cs
index 1835bd5e..37970024 100644
--- a/SabreTools.Models/Listxml/Adjuster.cs
+++ b/SabreTools.Models/Listxml/Adjuster.cs
@@ -11,7 +11,7 @@ namespace SabreTools.Models.Listxml
 
         /// <remarks>(yes|no) "no"</remarks>
         [XmlAttribute("default")]
-        public string Default { get; set; }
+        public string? Default { get; set; }
 
         [XmlElement("condition")]
         public Condition? Condition { get; set; }
diff --git a/SabreTools.Models/Listxml/Chip.cs b/SabreTools.Models/Listxml/Chip.cs
index 9ce6ddf4..56cf0ee6 100644
--- a/SabreTools.Models/Listxml/Chip.cs
+++ b/SabreTools.Models/Listxml/Chip.cs
@@ -18,7 +18,7 @@ namespace SabreTools.Models.Listxml
 
         /// <remarks>Only present in older versions</remarks>
         [XmlAttribute("soundonly")]
-        public string SoundOnly { get; set; }
+        public string? SoundOnly { get; set; }
 
         [XmlAttribute("clock")]
         public string? Clock { get; set; }
diff --git a/SabreTools.Models/Listxml/Driver.cs b/SabreTools.Models/Listxml/Driver.cs
index b339fc03..23ca06fe 100644
--- a/SabreTools.Models/Listxml/Driver.cs
+++ b/SabreTools.Models/Listxml/Driver.cs
@@ -12,15 +12,15 @@ namespace SabreTools.Models.Listxml
 
         /// <remarks>(good|imperfect|preliminary), Only present in older versions</remarks>
         [XmlAttribute("color")]
-        public string Color { get; set; }
+        public string? Color { get; set; }
 
         /// <remarks>(good|imperfect|preliminary), Only present in older versions</remarks>
         [XmlAttribute("sound")]
-        public string Sound { get; set; }
+        public string? Sound { get; set; }
 
         /// <remarks>Only present in older versions</remarks>
         [XmlAttribute("palettesize")]
-        public string PaletteSize { get; set; }
+        public string? PaletteSize { get; set; }
 
         /// <remarks>(good|imperfect|preliminary)</remarks>
         [XmlAttribute("emulation")]
diff --git a/SabreTools.Models/Listxml/Input.cs b/SabreTools.Models/Listxml/Input.cs
index 281613ba..a16f9cb0 100644
--- a/SabreTools.Models/Listxml/Input.cs
+++ b/SabreTools.Models/Listxml/Input.cs
@@ -24,7 +24,7 @@ namespace SabreTools.Models.Listxml
 
         /// <remarks>Only present in older versions, Numeric?</remarks>
         [XmlAttribute("buttons")]
-        public string Buttons { get; set; }
+        public string? Buttons { get; set; }
 
         /// <remarks>Numeric?</remarks>
         [XmlAttribute("coins")]