diff --git a/src/OpenIddict.Abstractions/Primitives/OpenIddictParameter.cs b/src/OpenIddict.Abstractions/Primitives/OpenIddictParameter.cs
index 4f1071c3..30854a39 100644
--- a/src/OpenIddict.Abstractions/Primitives/OpenIddictParameter.cs
+++ b/src/OpenIddict.Abstractions/Primitives/OpenIddictParameter.cs
@@ -77,6 +77,22 @@ namespace OpenIddict.Abstractions
         /// <returns>An <see cref="OpenIddictParameter"/> instance containing the item value.</returns>
         public OpenIddictParameter? this[string name] => GetNamedParameter(name);
 
+        /// <summary>
+        /// Gets the number of unnamed child items contained in the current parameter or
+        /// <c>0</c> if the parameter doesn't represent an array of strings or a JSON array.
+        /// </summary>
+        public int Count => Value switch
+        {
+            // If the parameter is a primitive array of strings, return its length.
+            string[] value => value.Length,
+
+            // If the parameter is a JSON array, return its length.
+            JsonElement value when value.ValueKind == JsonValueKind.Array => value.GetArrayLength(),
+
+            // Otherwise, return 0.
+            _ => 0
+        };
+
         /// <summary>
         /// Gets the associated value, that can be either a primitive CLR type
         /// (e.g bool, string, long), an array of strings or a complex JSON object.
diff --git a/test/OpenIddict.Abstractions.Tests/Primitives/OpenIddictParameterTests.cs b/test/OpenIddict.Abstractions.Tests/Primitives/OpenIddictParameterTests.cs
index d6b0a115..a35e041b 100644
--- a/test/OpenIddict.Abstractions.Tests/Primitives/OpenIddictParameterTests.cs
+++ b/test/OpenIddict.Abstractions.Tests/Primitives/OpenIddictParameterTests.cs
@@ -9,7 +9,6 @@ using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using System.Text;
-using System.Text.Encodings.Web;
 using System.Text.Json;
 using Xunit;
 
@@ -17,6 +16,82 @@ namespace OpenIddict.Abstractions.Tests.Primitives
 {
     public class OpenIddictParameterTests
     {
+        [Fact]
+        public void Count_ReturnsZeroForNullValue()
+        {
+            // Arrange
+            var parameter = new OpenIddictParameter();
+
+            // Act and assert
+            Assert.Equal(0, parameter.Count);
+        }
+
+        [Fact]
+        public void Count_ReturnsZeroForBoolean()
+        {
+            // Arrange
+            var parameter = new OpenIddictParameter(true);
+
+            // Act and assert
+            Assert.Equal(0, parameter.Count);
+        }
+
+        [Fact]
+        public void Count_ReturnsZeroForInteger()
+        {
+            // Arrange
+            var parameter = new OpenIddictParameter(42);
+
+            // Act and assert
+            Assert.Equal(0, parameter.Count);
+        }
+
+        [Fact]
+        public void Count_ReturnsZeroForString()
+        {
+            // Arrange
+            var parameter = new OpenIddictParameter("Fabrikam");
+
+            // Act and assert
+            Assert.Equal(0, parameter.Count);
+        }
+
+        [Fact]
+        public void Count_ReturnsExpectedValueForArray()
+        {
+            // Arrange
+            var parameter = new OpenIddictParameter(new[]
+            {
+                "Fabrikam",
+                "Contoso"
+            });
+
+            // Act and assert
+            Assert.Equal(2, parameter.Count);
+        }
+
+        [Fact]
+        public void Count_ReturnsExpectedValueForJsonArray()
+        {
+            // Arrange
+            var parameter = new OpenIddictParameter(
+                JsonSerializer.Deserialize<JsonElement>(@"[""Fabrikam"",""Contoso""]"));
+
+            // Act and assert
+            Assert.Equal(2, parameter.Count);
+        }
+
+        [Fact]
+        public void Count_ReturnsZeroForJsonObjects()
+        {
+            // Arrange
+            var parameter = new OpenIddictParameter(
+                JsonSerializer.Deserialize<JsonElement>(@"{""parameter"":""value""}"));
+
+            // Act and assert
+            Assert.Equal(0, parameter.Count);
+        }
+
         [Fact]
         public void Equals_ReturnsTrueWhenBothParametersAreNull()
         {