diff --git a/src/Aspire.Cli/Commands/NewCommand.cs b/src/Aspire.Cli/Commands/NewCommand.cs
index 884dfc88ad8..81cf290f4f3 100644
--- a/src/Aspire.Cli/Commands/NewCommand.cs
+++ b/src/Aspire.Cli/Commands/NewCommand.cs
@@ -222,12 +222,21 @@ public virtual async Task<ITemplate> PromptForTemplateAsync(ITemplate[] validTem
 
 internal static partial class ProjectNameValidator
 {
-    [GeneratedRegex(@"^[a-zA-Z0-9_][a-zA-Z0-9_.]{0,253}[a-zA-Z0-9_]$", RegexOptions.Compiled)]
-    internal static partial Regex GetAssemblyNameRegex();
+    // Regex for project name validation:
+    // - Can be any characters except path separators (/ and \)
+    // - Length: 1-254 characters
+    // - Must not be empty or whitespace only
+    [GeneratedRegex(@"^[^/\\]{1,254}$", RegexOptions.Compiled)]
+    internal static partial Regex GetProjectNameRegex();
 
     public static bool IsProjectNameValid(string projectName)
     {
-        var regex = GetAssemblyNameRegex();
+        if (string.IsNullOrWhiteSpace(projectName))
+        {
+            return false;
+        }
+
+        var regex = GetProjectNameRegex();
         return regex.IsMatch(projectName);
     }
 }
diff --git a/tests/Aspire.Cli.Tests/Commands/ProjectNameValidatorTests.cs b/tests/Aspire.Cli.Tests/Commands/ProjectNameValidatorTests.cs
new file mode 100644
index 00000000000..cdaaa083a65
--- /dev/null
+++ b/tests/Aspire.Cli.Tests/Commands/ProjectNameValidatorTests.cs
@@ -0,0 +1,172 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Aspire.Cli.Commands;
+using Xunit;
+
+namespace Aspire.Cli.Tests.Commands;
+
+public class ProjectNameValidatorTests
+{
+    [Theory]
+    [InlineData("项目1", true)]  // Chinese
+    [InlineData("Проект1", true)]  // Cyrillic
+    [InlineData("プロジェクト1", true)]  // Japanese
+    [InlineData("مشروع1", true)]  // Arabic
+    [InlineData("Project_1", true)]  // Latin with underscore
+    [InlineData("Project-1", true)]  // Latin with dash
+    [InlineData("Project.1", true)]  // Latin with dot
+    [InlineData("MyApp", true)]  // Simple ASCII
+    [InlineData("A", true)]  // Single character
+    [InlineData("1", true)]  // Single number
+    [InlineData("プ", true)]  // Single Unicode character
+    [InlineData("Test123", true)]  // Mixed letters and numbers
+    [InlineData("My_Cool-Project.v2", true)]  // Complex valid name
+    [InlineData("Project:1", true)]  // Colon (now allowed)
+    [InlineData("Project*1", true)]  // Asterisk (now allowed)
+    [InlineData("Project?1", true)]  // Question mark (now allowed)
+    [InlineData("Project\"1", true)]  // Quote (now allowed)
+    [InlineData("Project<1", true)]  // Less than (now allowed)
+    [InlineData("Project>1", true)]  // Greater than (now allowed)
+    [InlineData("Project|1", true)]  // Pipe (now allowed)
+    [InlineData("Project ", true)]  // Ends with space (now allowed)
+    [InlineData(" Project", true)]  // Starts with space (now allowed)
+    [InlineData("Pro ject", true)]  // Space in middle (now allowed)
+    [InlineData("-Project", true)]  // Starts with dash (now allowed)
+    [InlineData("Project-", true)]  // Ends with dash (now allowed)
+    [InlineData(".Project", true)]  // Starts with dot (now allowed)
+    [InlineData("Project.", true)]  // Ends with dot (now allowed)
+    [InlineData("_Project", true)]  // Starts with underscore (now allowed)
+    [InlineData("Project_", true)]  // Ends with underscore (now allowed)
+    public void IsProjectNameValid_ValidNames_ReturnsTrue(string projectName, bool expected)
+    {
+        // Act
+        var result = ProjectNameValidator.IsProjectNameValid(projectName);
+
+        // Assert
+        Assert.Equal(expected, result);
+    }
+
+    [Theory]
+    [InlineData("Project/1", false)]  // Forward slash (path separator)
+    [InlineData("Project\\1", false)]  // Backslash (path separator)
+    [InlineData("", false)]  // Empty string
+    [InlineData(" ", false)]  // Space only
+    [InlineData("   ", false)]  // Multiple spaces only
+    [InlineData("\t", false)]  // Tab only
+    [InlineData("\n", false)]  // Newline only
+    public void IsProjectNameValid_InvalidNames_ReturnsFalse(string projectName, bool expected)
+    {
+        // Act
+        var result = ProjectNameValidator.IsProjectNameValid(projectName);
+
+        // Assert
+        Assert.Equal(expected, result);
+    }
+
+    [Fact]
+    public void IsProjectNameValid_MaxLength254_ReturnsTrue()
+    {
+        // Arrange
+        var projectName = new string('A', 254);
+
+        // Act
+        var result = ProjectNameValidator.IsProjectNameValid(projectName);
+
+        // Assert
+        Assert.True(result);
+    }
+
+    [Fact]
+    public void IsProjectNameValid_Length255_ReturnsFalse()
+    {
+        // Arrange
+        var projectName = new string('A', 255);
+
+        // Act
+        var result = ProjectNameValidator.IsProjectNameValid(projectName);
+
+        // Assert
+        Assert.False(result);
+    }
+
+    [Theory]
+    [InlineData("项目测试名称很长的中文项目名称")]  // Long Chinese name
+    [InlineData("очень_длинное_русское_имя_проекта")]  // Long Russian name
+    [InlineData("とても長い日本語のプロジェクト名")]  // Long Japanese name
+    [InlineData("اسم_مشروع_طويل_جدا_بالعربية")]  // Long Arabic name
+    public void IsProjectNameValid_LongUnicodeNames_ReturnsTrue(string projectName)
+    {
+        // Act
+        var result = ProjectNameValidator.IsProjectNameValid(projectName);
+
+        // Assert
+        Assert.True(result, $"Unicode project name should be valid: {projectName}");
+    }
+
+    [Theory]
+    [InlineData("Ελληνικά", true)]  // Greek
+    [InlineData("עברית", true)]  // Hebrew
+    [InlineData("हिन्दी", true)]  // Hindi
+    [InlineData("ไทย", true)]  // Thai
+    [InlineData("한국어", true)]  // Korean
+    [InlineData("Türkçe", true)]  // Turkish
+    [InlineData("Português", true)]  // Portuguese with accent
+    [InlineData("Français", true)]  // French with accent
+    [InlineData("Español", true)]  // Spanish with accent
+    [InlineData("Deutsch", true)]  // German
+    public void IsProjectNameValid_VariousLanguages_ReturnsTrue(string projectName, bool expected)
+    {
+        // Act
+        var result = ProjectNameValidator.IsProjectNameValid(projectName);
+
+        // Assert
+        Assert.Equal(expected, result);
+    }
+
+    [Theory]
+    [InlineData("Test123-Project_Name.v2")]  // Complex valid with all allowed characters
+    [InlineData("A1-B2_C3.D4")]  // Mixed with separators
+    [InlineData("项目-测试_版本.1")]  // Unicode with separators
+    public void IsProjectNameValid_ComplexValidNames_ReturnsTrue(string projectName)
+    {
+        // Act
+        var result = ProjectNameValidator.IsProjectNameValid(projectName);
+
+        // Assert
+        Assert.True(result, $"Complex valid project name should be valid: {projectName}");
+    }
+
+    [Theory]
+    [InlineData("Test..Name")]  // Double dot
+    [InlineData("Test--Name")]  // Double dash
+    [InlineData("Test__Name")]  // Double underscore
+    public void IsProjectNameValid_ConsecutiveSpecialChars_ReturnsTrue(string projectName)
+    {
+        // These should be valid as the spec doesn't prohibit consecutive allowed characters
+        // Act
+        var result = ProjectNameValidator.IsProjectNameValid(projectName);
+
+        // Assert
+        Assert.True(result, $"Consecutive allowed characters should be valid: {projectName}");
+    }
+
+    [Theory]
+    [InlineData("My/Project")]  // Forward slash in middle
+    [InlineData("/MyProject")]  // Forward slash at start
+    [InlineData("MyProject/")]  // Forward slash at end
+    [InlineData("My\\Project")]  // Backslash in middle
+    [InlineData("\\MyProject")]  // Backslash at start
+    [InlineData("MyProject\\")]  // Backslash at end
+    [InlineData("My/Project/Name")]  // Multiple forward slashes
+    [InlineData("My\\Project\\Name")]  // Multiple backslashes
+    [InlineData("My/Project\\Name")]  // Mixed path separators
+    public void IsProjectNameValid_PathSeparators_ReturnsFalse(string projectName)
+    {
+        // Act
+        var result = ProjectNameValidator.IsProjectNameValid(projectName);
+
+        // Assert
+        Assert.False(result, $"Project name with path separators should be invalid: {projectName}");
+    }
+}
\ No newline at end of file