diff --git a/Elwig/App.xaml.cs b/Elwig/App.xaml.cs
index f67678c..eeb3805 100644
--- a/Elwig/App.xaml.cs
+++ b/Elwig/App.xaml.cs
@@ -16,6 +16,7 @@ using Elwig.Helpers.Printing;
 using Elwig.Windows;
 using Elwig.Dialogs;
 using System.Threading.Tasks;
+using Elwig.Helpers.Billing;
 
 namespace Elwig {
     public partial class App : Application {
@@ -104,6 +105,7 @@ namespace Elwig {
 
             Utils.RunBackground("HTML Initialization", () => Html.Init(PrintingReadyChanged));
             Utils.RunBackground("PDF Initialization", () => Pdf.Init(PrintingReadyChanged));
+            Utils.RunBackground("JSON Schema Initialization", BillingData.Init);
 
             var list = new List<IScale>();
             foreach (var s in Config.Scales) {
diff --git a/Elwig/Elwig.csproj b/Elwig/Elwig.csproj
index 32a5d30..d574c3a 100644
--- a/Elwig/Elwig.csproj
+++ b/Elwig/Elwig.csproj
@@ -14,6 +14,7 @@
   <ItemGroup>
     <Resource Include="Resources\Images\Elwig.png" />
     <Content Include="Resources\Images\Elwig.ico" />
+	<EmbeddedResource Include="Schemas\payment_variant.json" />
   </ItemGroup>
 
   <Target Name="PreBuild" BeforeTargets="PreBuildEvent">
@@ -28,6 +29,7 @@
     <PackageReference Include="Microsoft.EntityFrameworkCore.Sqlite" Version="8.0.0" />
     <PackageReference Include="Microsoft.Extensions.Configuration.Ini" Version="8.0.0" />
     <PackageReference Include="Microsoft.Web.WebView2" Version="1.0.2151.40" />
+    <PackageReference Include="NJsonSchema" Version="11.0.0" />
     <PackageReference Include="RazorLight" Version="2.3.1" />
     <PackageReference Include="ScottPlot.WPF" Version="4.1.68" />
     <PackageReference Include="System.IO.Ports" Version="8.0.0" />
diff --git a/Elwig/Helpers/Billing/BillingData.cs b/Elwig/Helpers/Billing/BillingData.cs
new file mode 100644
index 0000000..986e59d
--- /dev/null
+++ b/Elwig/Helpers/Billing/BillingData.cs
@@ -0,0 +1,44 @@
+using Newtonsoft.Json;
+using NJsonSchema;
+using System;
+using System.Reflection;
+using System.Text.Json.Nodes;
+using System.Threading.Tasks;
+
+namespace Elwig.Helpers.Billing {
+    public class BillingData {
+
+        public static JsonSchema? Schema { get; private set; }
+
+        public static async Task Init() {
+            var stream = Assembly.GetExecutingAssembly().GetManifestResourceStream("Elwig.Schemas.payment_variant.json");
+            Schema = await JsonSchema.FromJsonAsync(stream ?? throw new ArgumentException("JSON schema not found"));
+        }
+
+        private JsonObject Data;
+
+        public BillingData(JsonObject data) {
+            Data = data;
+
+        }
+
+        public static JsonObject ParseJson(string json) {
+            if (Schema == null) throw new InvalidOperationException("Schema has to be initialized first");
+            try {
+                var errors = Schema.Validate(json);
+                if (errors.Count != 0) throw new ArgumentException("Invalid JSON data");
+                return JsonNode.Parse(json)?.AsObject() ?? throw new ArgumentException("Invalid JSON data");
+            } catch (JsonReaderException) {
+                throw new ArgumentException("Invalid JSON data");
+            }
+        }
+
+        public static BillingData FromJson(string json) {
+            return new(ParseJson(json));
+        }
+
+        public decimal CalculatePrice(string sortId, string? attrid, string qualId, bool gebunden, double oe, double kmw, bool minQuw) {
+            return 0m;
+        }
+    }
+}
diff --git a/Elwig/Schemas/payment_variant.json b/Elwig/Schemas/payment_variant.json
new file mode 100644
index 0000000..af7e86b
--- /dev/null
+++ b/Elwig/Schemas/payment_variant.json
@@ -0,0 +1,135 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "type": "object",
+  "required": ["mode"],
+  "anyOf": [{
+    "required": ["version", "payment", "curves"],
+    "additionalProperties": false,
+    "properties": {
+      "mode": {"enum": ["elwig"]},
+      "version": {"enum": [1]},
+      "payment": {
+        "type": ["number", "string", "object"],
+        "pattern": "^curve:[0-9]+$",
+        "additionalProperties": false,
+        "properties": {
+          "default": {
+            "type": ["number", "string"],
+            "pattern": "^curve:[0-9]+$"
+          }
+        },
+        "patternProperties": {
+          "^[A-Z]+$": {
+            "type": ["number", "string"],
+            "pattern": "^curve:[0-9]+$"
+          }
+        }
+      },
+      "quality": {
+        "type": "object",
+        "additionalProperties": false,
+        "patternProperties": {
+          "^[A-Z]{3}$": {
+            "type": ["number", "string", "object"],
+            "pattern": "^curve:[0-9]+$",
+            "additionalProperties": false,
+            "properties": {
+              "default": {
+                "type": ["number", "string"],
+                "pattern": "^curve:[0-9]+$"
+              }
+            },
+            "patternProperties": {
+              "^[A-Z]+$": {
+                "type": ["number", "string"],
+                "pattern": "^curve:[0-9]+$"
+              }
+            }
+          }
+        }
+      },
+      "curves": {
+        "type": "array",
+        "items": {"$ref": "#/definitions/curve"}
+      }
+    }
+  }, {
+    "properties": {
+      "mode": {"enum": ["wgmaster"]},
+      "AuszahlungSorten": {
+        "type": "object",
+        "additionalProperties": false,
+        "required": ["Kurven"],
+        "properties": {
+          "Kurven": {
+            "type": "array",
+            "items": {
+              "type": "object",
+              "additionalProperties": false,
+              "minProperties": 1,
+              "patternProperties": {
+                "^[0-9]+(\\.[0-9]+)?oe$": {"type": "number"}
+              }
+            }
+          }
+        },
+        "patternProperties": {
+          "^[A-Z]{2}$": {
+            "type": "object",
+            "additionalProperties": false,
+            "patternProperties": {
+              "^[A-Z]*$": {
+                "type": "object",
+                "additionalProperties": false,
+                "properties": {
+                  "Gebunden": {
+                    "type": "integer",
+                    "minimum": 0
+                  },
+                  "NichtGebunden": {
+                    "type": "integer",
+                    "minimum": 0
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+  }],
+  "definitions": {
+    "curve": {
+      "type": "object",
+      "required": ["id", "mode", "data"],
+      "additionalProperties": false,
+      "properties": {
+        "id": {
+          "type": "integer",
+          "minimum": 0
+        },
+        "mode": {"enum": ["oe", "kmw"]},
+        "data": {
+          "anyOf": [
+            {"type": "number" },
+            {"$ref": "#/definitions/curve_data"}
+         ]
+        },
+        "geb": {
+          "anyOf": [
+            {"type": "number"},
+            {"$ref": "#/definitions/curve_data"}
+         ]
+        }
+      }
+    },
+    "curve_data": {
+      "type": "object",
+      "additionalProperties": false,
+      "minProperties": 1,
+      "patternProperties": {
+        "^([0-9]+(\\.[0-9]+)?)(oe|kmw)$": {"type": "number"}
+      }
+    }
+  }
+}
diff --git a/Elwig/Windows/ChartWindow.xaml.cs b/Elwig/Windows/ChartWindow.xaml.cs
index 1f2e2ff..1466b99 100644
--- a/Elwig/Windows/ChartWindow.xaml.cs
+++ b/Elwig/Windows/ChartWindow.xaml.cs
@@ -63,8 +63,8 @@ namespace Elwig.Windows {
 
         private static JsonObject? ParseData(PaymentVar variant) {
             try {
-                return JsonNode.Parse(variant.Data)?.AsObject();
-            } catch (JsonException) {
+                return BillingData.ParseJson(variant.Data);
+            } catch (ArgumentException) {
                 return null;
             }
         }