diff --git a/Marechai.Server/Helpers/CharRouteConstraint.cs b/Marechai.Server/Helpers/CharRouteConstraint.cs
new file mode 100644
index 00000000..31296f2d
--- /dev/null
+++ b/Marechai.Server/Helpers/CharRouteConstraint.cs
@@ -0,0 +1,43 @@
+/******************************************************************************
+// MARECHAI: Master repository of computing history artifacts information
+// ----------------------------------------------------------------------------
+//
+// Author(s)      : Natalia Portillo <claunia@claunia.com>
+//
+// --[ License ] --------------------------------------------------------------
+//
+//     This program is free software: you can redistribute it and/or modify
+//     it under the terms of the GNU General Public License as
+//     published by the Free Software Foundation, either version 3 of the
+//     License, or (at your option) any later version.
+//
+//     This program is distributed in the hope that it will be useful,
+//     but WITHOUT ANY WARRANTY; without even the implied warranty of
+//     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//     GNU General Public License for more details.
+//
+//     You should have received a copy of the GNU General Public License
+//     along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+// ----------------------------------------------------------------------------
+// Copyright © 2003-2021 Natalia Portillo
+*******************************************************************************/
+
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Routing;
+
+namespace Marechai.Server.Helpers;
+
+/// <summary>Custom route constraint for char parameters</summary>
+public class CharRouteConstraint : IRouteConstraint
+{
+    public bool Match(HttpContext    httpContext, IRouter route, string routeKey, RouteValueDictionary values,
+                      RouteDirection routeDirection)
+    {
+        if(!values.TryGetValue(routeKey, out object value)) return false;
+
+        string stringValue = value?.ToString() ?? string.Empty;
+
+        return stringValue.Length == 1 && char.TryParse(stringValue, out _);
+    }
+}
\ No newline at end of file
diff --git a/Marechai.Server/Helpers/UlongRouteConstraint.cs b/Marechai.Server/Helpers/UlongRouteConstraint.cs
new file mode 100644
index 00000000..5cf3518c
--- /dev/null
+++ b/Marechai.Server/Helpers/UlongRouteConstraint.cs
@@ -0,0 +1,41 @@
+/******************************************************************************
+// MARECHAI: Master repository of computing history artifacts information
+// ----------------------------------------------------------------------------
+//
+// Author(s)      : Natalia Portillo <claunia@claunia.com>
+//
+// --[ License ] --------------------------------------------------------------
+//
+//     This program is free software: you can redistribute it and/or modify
+//     it under the terms of the GNU General Public License as
+//     published by the Free Software Foundation, either version 3 of the
+//     License, or (at your option) any later version.
+//
+//     This program is distributed in the hope that it will be useful,
+//     but WITHOUT ANY WARRANTY; without even the implied warranty of
+//     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//     GNU General Public License for more details.
+//
+//     You should have received a copy of the GNU General Public License
+//     along with this program.  If not, see <http://www.gnu.org/licenses/>.
+//
+// ----------------------------------------------------------------------------
+// Copyright © 2003-2021 Natalia Portillo
+*******************************************************************************/
+
+using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Routing;
+
+namespace Marechai.Server.Helpers;
+
+/// <summary>Custom route constraint for ulong parameters</summary>
+public class UlongRouteConstraint : IRouteConstraint
+{
+    public bool Match(HttpContext    httpContext, IRouter route, string routeKey, RouteValueDictionary values,
+                      RouteDirection routeDirection)
+    {
+        if(!values.TryGetValue(routeKey, out object value)) return false;
+
+        return ulong.TryParse(value?.ToString() ?? string.Empty, out _);
+    }
+}
\ No newline at end of file
diff --git a/Marechai.Server/Program.cs b/Marechai.Server/Program.cs
index 786bd31e..5a330b2b 100644
--- a/Marechai.Server/Program.cs
+++ b/Marechai.Server/Program.cs
@@ -1,6 +1,7 @@
 using System;
 using System.Linq;
 using System.Text.Json;
+using System.Text.Json.Serialization;
 using Aaru.CommonTypes.Interop;
 using Marechai.Database;
 using Marechai.Database.Models;
@@ -10,6 +11,7 @@ using Marechai.Server.Services;
 using Markdig;
 using Microsoft.AspNetCore.Authentication.JwtBearer;
 using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.Routing;
 using Microsoft.EntityFrameworkCore;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
@@ -21,7 +23,7 @@ namespace Marechai.Server;
 
 file class Program
 {
-    static IDbCore _database;
+    private static IDbCore _database;
 
     public static void Main(string[] args)
     {
@@ -154,11 +156,19 @@ file class Program
                     options.JsonSerializerOptions.Converters.Add(new IsoDateTimeConverter());
                     options.JsonSerializerOptions.PropertyNamingPolicy = JsonNamingPolicy.CamelCase;
                     options.JsonSerializerOptions.WriteIndented        = true;
+                    options.JsonSerializerOptions.ReferenceHandler     = ReferenceHandler.IgnoreCycles;
                 });
 
         // Learn more about configuring OpenAPI at https://aka.ms/aspnet/openapi
         builder.Services.AddOpenApi();
 
+        // Add custom route constraints
+        builder.Services.Configure<RouteOptions>(options =>
+        {
+            options.ConstraintMap["ulong"] = typeof(UlongRouteConstraint);
+            options.ConstraintMap["char"]  = typeof(CharRouteConstraint);
+        });
+
         builder.Services.AddAuthentication(options =>
                 {
                     options.DefaultAuthenticateScheme = JwtBearerDefaults.AuthenticationScheme;