diff --git a/HellionChat/Themes/ThemeJsonLoader.cs b/HellionChat/Themes/ThemeJsonLoader.cs
new file mode 100644
index 0000000..d73200f
--- /dev/null
+++ b/HellionChat/Themes/ThemeJsonLoader.cs
@@ -0,0 +1,106 @@
+using System.Text.Json;
+using HellionChat.Util;
+
+namespace HellionChat.Themes;
+
+internal static class ThemeJsonLoader
+{
+    public const int SupportedSchemaVersion = 1;
+
+    public static Theme LoadFromString(string json)
+    {
+        if (string.IsNullOrWhiteSpace(json))
+            throw new FormatException("Theme JSON is empty");
+
+        JsonDocument doc;
+        try { doc = JsonDocument.Parse(json); }
+        catch (JsonException ex) { throw new FormatException("Theme JSON is not valid JSON", ex); }
+
+        using (doc)
+        {
+            var root = doc.RootElement;
+
+            var schemaVersion = ReadInt(root, "schemaVersion");
+            if (schemaVersion != SupportedSchemaVersion)
+                throw new FormatException($"Unsupported schemaVersion {schemaVersion}; expected {SupportedSchemaVersion}");
+
+            var slug        = ReadString(root, "slug");
+            var name        = ReadString(root, "name");
+            var author      = ReadString(root, "author");
+            var description = ReadString(root, "description");
+
+            var colors = ReadColors(root.GetProperty("colors"));
+            var layout = ReadLayout(root.GetProperty("layout"));
+
+            return new Theme(slug, name, author, description, colors, layout, new ThemeTypography(), IsBuiltIn: false);
+        }
+    }
+
+    public static Theme LoadFromFile(string path)
+    {
+        var json = File.ReadAllText(path);
+        return LoadFromString(json);
+    }
+
+    private static ThemeColors ReadColors(JsonElement el) => new(
+        PrimaryDark:   ColourUtil.HexToRgba(ReadString(el, "primaryDark")),
+        Primary:       ColourUtil.HexToRgba(ReadString(el, "primary")),
+        PrimaryLight:  ColourUtil.HexToRgba(ReadString(el, "primaryLight")),
+        PrimaryGlow:   ColourUtil.HexToRgba(ReadString(el, "primaryGlow")),
+
+        AccentDark:    ColourUtil.HexToRgba(ReadString(el, "accentDark")),
+        Accent:        ColourUtil.HexToRgba(ReadString(el, "accent")),
+        AccentLight:   ColourUtil.HexToRgba(ReadString(el, "accentLight")),
+
+        Identity:      ColourUtil.HexToRgba(ReadString(el, "identity")),
+
+        WindowBg:      ColourUtil.HexToRgba(ReadString(el, "windowBg")),
+        ChildBg:       ColourUtil.HexToRgba(ReadString(el, "childBg")),
+        FrameBg:       ColourUtil.HexToRgba(ReadString(el, "frameBg")),
+        Surface:       ColourUtil.HexToRgba(ReadString(el, "surface")),
+        SurfaceHover:  ColourUtil.HexToRgba(ReadString(el, "surfaceHover")),
+        Border:        ColourUtil.HexToRgba(ReadString(el, "border")),
+
+        TextPrimary:   ColourUtil.HexToRgba(ReadString(el, "textPrimary")),
+        TextMuted:     ColourUtil.HexToRgba(ReadString(el, "textMuted")),
+        TextDim:       ColourUtil.HexToRgba(ReadString(el, "textDim")),
+
+        StatusSuccess: ColourUtil.HexToRgba(ReadString(el, "statusSuccess")),
+        StatusDanger:  ColourUtil.HexToRgba(ReadString(el, "statusDanger")),
+        StatusWarning: ColourUtil.HexToRgba(ReadString(el, "statusWarning")),
+        StatusInfo:    ColourUtil.HexToRgba(ReadString(el, "statusInfo"))
+    );
+
+    private static ThemeLayout ReadLayout(JsonElement el) => new(
+        WindowRounding:    ReadFloat(el, "windowRounding"),
+        ChildRounding:     ReadFloat(el, "childRounding"),
+        PopupRounding:     ReadFloat(el, "popupRounding"),
+        FrameRounding:     ReadFloat(el, "frameRounding"),
+        GrabRounding:      ReadFloat(el, "grabRounding"),
+        TabRounding:       ReadFloat(el, "tabRounding"),
+        ScrollbarRounding: ReadFloat(el, "scrollbarRounding"),
+        WindowBorderSize:  ReadFloat(el, "windowBorderSize"),
+        FrameBorderSize:   ReadFloat(el, "frameBorderSize")
+    );
+
+    private static string ReadString(JsonElement el, string name)
+    {
+        if (!el.TryGetProperty(name, out var v) || v.ValueKind != JsonValueKind.String)
+            throw new FormatException($"Theme JSON missing string property '{name}'");
+        return v.GetString() ?? throw new FormatException($"Theme JSON property '{name}' is null");
+    }
+
+    private static int ReadInt(JsonElement el, string name)
+    {
+        if (!el.TryGetProperty(name, out var v) || v.ValueKind != JsonValueKind.Number)
+            throw new FormatException($"Theme JSON missing number property '{name}'");
+        return v.GetInt32();
+    }
+
+    private static float ReadFloat(JsonElement el, string name)
+    {
+        if (!el.TryGetProperty(name, out var v) || v.ValueKind != JsonValueKind.Number)
+            throw new FormatException($"Theme JSON missing number property '{name}'");
+        return (float)v.GetDouble();
+    }
+}