diff --git a/pkgs/shared/common/src/Helpers/ValidationUtils.cs b/pkgs/shared/common/src/Helpers/ValidationUtils.cs
index 7a11780d..b66b84cb 100644
--- a/pkgs/shared/common/src/Helpers/ValidationUtils.cs
+++ b/pkgs/shared/common/src/Helpers/ValidationUtils.cs
@@ -9,9 +9,36 @@ namespace LaunchDarkly.Sdk.Helpers
     public static class ValidationUtils
     {
         private static readonly Regex ValidCharsRegex = new Regex("^[-a-zA-Z0-9._]+\\z");
+        private const int MaxSdkKeyLength = 8192;
 
         /// <summary>
-        /// Validates that a string is non-empty, not too longer for our systems, and only contains
+        /// Validates that a string does not contain invalid characters and is not too long for our systems.
+        /// </summary>
+        /// <param name="sdkKey">the SDK key to validate.</param>
+        /// <returns>True if the SDK key format is valid, otherwise false.</returns>
+        public static bool IsValidSdkKeyFormat(string sdkKey)
+        {
+            // For offline mode, we allow a null or empty SDK key and it is not invalid.
+            if (string.IsNullOrEmpty(sdkKey))
+            {
+                return true;
+            }
+
+            if (sdkKey.Length > MaxSdkKeyLength)
+            {
+                return false;
+            }
+
+            if (!ValidCharsRegex.IsMatch(sdkKey))
+            {
+                return false;
+            }
+
+            return true;
+        }
+
+        /// <summary>
+        /// Validates that a string is non-empty, not too long for our systems, and only contains
         /// alphanumeric characters, hyphens, periods, and underscores.
         /// </summary>
         /// <param name="s">the string to validate.</param>
diff --git a/pkgs/shared/common/test/Helpers/ValidationUtilsTest.cs b/pkgs/shared/common/test/Helpers/ValidationUtilsTest.cs
index 26f9c342..12d56aa9 100644
--- a/pkgs/shared/common/test/Helpers/ValidationUtilsTest.cs
+++ b/pkgs/shared/common/test/Helpers/ValidationUtilsTest.cs
@@ -4,18 +4,60 @@ namespace LaunchDarkly.Sdk.Helpers
 {
     public class ValidationUtilsTest
     {
+        [Theory]
+        [InlineData(null)]
+        [InlineData("")]
+        public void IsValidSdkKeyFormat_EmptyOrNullKey_ReturnsTrue(string key)
+        {
+            Assert.True(ValidationUtils.IsValidSdkKeyFormat(key));
+        }
+
+        [Theory]
+        [InlineData("sdk-key-123")]
+        [InlineData("sdk.key.123")]
+        [InlineData("sdk_key_123")]
+        [InlineData("SDKKEY123")]
+        public void IsValidSdkKeyFormat_ValidKey_ReturnsTrue(string key)
+        {
+            Assert.True(ValidationUtils.IsValidSdkKeyFormat(key));
+        }
+
         [Fact]
-        public void ValidateStringValue()
+        public void IsValidSdkKeyFormat_TooLongKey_ReturnsFalseWithError()
+        {
+            var longKey = new string('a', 8193); // Creates a string longer than MaxSdkKeyLength (8192)
+            Assert.False(ValidationUtils.IsValidSdkKeyFormat(longKey));
+        }
+
+        [Theory]
+        [InlineData("sdk key")] // Contains space
+        [InlineData("sdk#key")] // Contains special character
+        [InlineData("sdk/key")] // Contains slash
+        [InlineData("sdk\nkey")] // Contains newline
+        public void IsValidSdkKeyFormat_InvalidCharacters_ReturnsFalseWithError(string key)
+        {
+            Assert.False(ValidationUtils.IsValidSdkKeyFormat(key));
+        }
+
+        [Theory]
+        [InlineData("bad-\n")] // Contains newline
+        [InlineData("bad-\t")] // Contains tab
+        [InlineData("###invalid")] // Contains special characters
+        [InlineData("")]  // Empty string
+        [InlineData("0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEFwhoops")] // Too long
+        [InlineData("#@$%^&")] // Invalid characters
+        public void ValidateStringValue_Invalid_ReturnsErrorMessage(string input)
+        {
+            Assert.NotNull(ValidationUtils.ValidateStringValue(input));
+        }
+
+        [Theory]
+        [InlineData("a-Az-Z0-9._-")]
+        [InlineData("valid-string-123")]
+        [InlineData("VALIDSTRING")]
+        public void ValidateStringValue_Valid_ReturnsNull(string input)
         {
-            Assert.NotNull(ValidationUtils.ValidateStringValue("bad-\n"));
-            Assert.NotNull(ValidationUtils.ValidateStringValue("bad-\t"));
-            Assert.NotNull(ValidationUtils.ValidateStringValue("###invalid"));
-            Assert.NotNull(ValidationUtils.ValidateStringValue(""));
-            Assert.NotNull(
-                ValidationUtils.ValidateStringValue(
-                    "0123456789ABCDEF0123456789ABCDEF0123456789ABCDEF0123456789ABCDEFwhoops"));
-            Assert.NotNull(ValidationUtils.ValidateStringValue("#@$%^&"));
-            Assert.Null(ValidationUtils.ValidateStringValue("a-Az-Z0-9._-"));
+            Assert.Null(ValidationUtils.ValidateStringValue(input));
         }
 
         [Fact]