Index: Core/Common/src/Core.Common.Utils/Extensions/StringExtensions.cs
===================================================================
diff -u -r1a062846c75d2d86454dc052adc7a5993b79963e -r24ed17047f5f34a54a707b3283d97f36e1b67f58
--- Core/Common/src/Core.Common.Utils/Extensions/StringExtensions.cs	(.../StringExtensions.cs)	(revision 1a062846c75d2d86454dc052adc7a5993b79963e)
+++ Core/Common/src/Core.Common.Utils/Extensions/StringExtensions.cs	(.../StringExtensions.cs)	(revision 24ed17047f5f34a54a707b3283d97f36e1b67f58)
@@ -43,7 +43,7 @@
         /// </summary>
         /// <param name="str">The string to set the first letter to upper case for.</param>
         /// <returns>A string with the first letter set to upper case.</returns>
-        public static string FirstLetterToUpper(this string str)
+        public static string FirstToUpper(this string str)
         {
             if (str == null)
             {
Index: Core/Common/test/Core.Common.Utils.Test/Extensions/StringExtensionsTest.cs
===================================================================
diff -u -r1a062846c75d2d86454dc052adc7a5993b79963e -r24ed17047f5f34a54a707b3283d97f36e1b67f58
--- Core/Common/test/Core.Common.Utils.Test/Extensions/StringExtensionsTest.cs	(.../StringExtensionsTest.cs)	(revision 1a062846c75d2d86454dc052adc7a5993b79963e)
+++ Core/Common/test/Core.Common.Utils.Test/Extensions/StringExtensionsTest.cs	(.../StringExtensionsTest.cs)	(revision 24ed17047f5f34a54a707b3283d97f36e1b67f58)
@@ -55,13 +55,13 @@
         }
 
         [Test]
-        public void FirstLetterToUpper_StringIsNull_ReturnNull()
+        public void FirstToUpper_StringIsNull_ReturnNull()
         {
             // Setup
             const string str = null;
 
             // Call
-            string result = str.FirstLetterToUpper();
+            string result = str.FirstToUpper();
 
             // Assert
             Assert.IsNull(result);
@@ -73,10 +73,10 @@
         [TestCase("Test", "Test")]
         [TestCase("tesT Test", "TesT Test")]
         [TestCase("TesT Test", "TesT Test")]
-        public void FirstLetterToUpper_StringIsNotNull_ReturnStringWithFirstLetterUpperCase(string str, string expectedResult)
+        public void FirstToUpper_StringIsNotNull_ReturnStringWithFirstLetterUpperCase(string str, string expectedResult)
         {
             // Call
-            string result = str.FirstLetterToUpper();
+            string result = str.FirstToUpper();
 
             // Assert
             Assert.AreEqual(expectedResult, result);
Index: Ringtoets/Common/src/Ringtoets.Common.IO/Structures/StructuresCharacteristicsCsvReader.cs
===================================================================
diff -u -r5241062f8df6b7a99943ce1983ce8947adc3d899 -r24ed17047f5f34a54a707b3283d97f36e1b67f58
--- Ringtoets/Common/src/Ringtoets.Common.IO/Structures/StructuresCharacteristicsCsvReader.cs	(.../StructuresCharacteristicsCsvReader.cs)	(revision 5241062f8df6b7a99943ce1983ce8947adc3d899)
+++ Ringtoets/Common/src/Ringtoets.Common.IO/Structures/StructuresCharacteristicsCsvReader.cs	(.../StructuresCharacteristicsCsvReader.cs)	(revision 24ed17047f5f34a54a707b3283d97f36e1b67f58)
@@ -263,7 +263,7 @@
                     else
                     {
                         string message = string.Format(Resources.StructuresCharacteristicsCsvReader_Column_0_must_be_defined_only_once,
-                                                       columnName.FirstLetterToUpper());
+                                                       columnName.FirstToUpper());
                         throw CreateCriticalFileReadException(lineNumber, message);
                     }
                 }
@@ -282,7 +282,7 @@
             if (requiredHeaderColumnIndices.Any(i => i == uninitializedValue))
             {
                 string message = string.Format(Resources.StructuresCharacteristicsCsvReader_ValidateRequiredColumnIndices_Invalid_header_Must_have_columns_0_,
-                                               string.Join(Environment.NewLine, requiredHeaderColumns.Select(rh => "* " + rh.FirstLetterToUpper())));
+                                               string.Join(Environment.NewLine, requiredHeaderColumns.Select(rh => "* " + rh.FirstToUpper())));
                 throw CreateCriticalFileReadException(lineNumber, message);
             }
         }
@@ -392,7 +392,7 @@
         private string ParseLocationId(string[] tokenizedText)
         {
             string locationId = tokenizedText[locationIdIndex];
-            return ParseIdString(locationId, StructureFilesKeywords.IdentificationColumnName.FirstLetterToUpper());
+            return ParseIdString(locationId, StructureFilesKeywords.IdentificationColumnName.FirstToUpper());
         }
 
         /// <summary>
@@ -405,7 +405,7 @@
         private string ParseParameterId(string[] tokenizedText)
         {
             string parameterId = tokenizedText[parameterIdIndex];
-            return ParseIdString(parameterId, StructureFilesKeywords.StructureIdentificationColumnName.FirstLetterToUpper());
+            return ParseIdString(parameterId, StructureFilesKeywords.StructureIdentificationColumnName.FirstToUpper());
         }
 
         private string ParseIdString(string parameterTextValue, string parameterName)
@@ -434,7 +434,7 @@
         private double ParseNumericValue(string[] tokenizedText)
         {
             string numericValueText = tokenizedText[numericValueIndex];
-            return ParseDoubleValue(numericValueText, StructureFilesKeywords.NumericalValueColumnName.FirstLetterToUpper());
+            return ParseDoubleValue(numericValueText, StructureFilesKeywords.NumericalValueColumnName.FirstToUpper());
         }
 
         /// <summary>
@@ -448,7 +448,7 @@
         private double ParseVarianceValue(string[] tokenizedText)
         {
             string varianceValueText = tokenizedText[varianceValueIndex];
-            return ParseDoubleValue(varianceValueText, StructureFilesKeywords.VariationValueColumnName.FirstLetterToUpper());
+            return ParseDoubleValue(varianceValueText, StructureFilesKeywords.VariationValueColumnName.FirstToUpper());
         }
 
         /// <summary>
@@ -508,20 +508,20 @@
                 }
                 throw CreateLineParseException(lineNumber,
                                                string.Format(Resources.StructuresCharacteristicsCsvReader_ParseVarianceType_ParameterName_0_only_allows_certain_values,
-                                                             StructureFilesKeywords.VariationTypeColumnName.FirstLetterToUpper()));
+                                                             StructureFilesKeywords.VariationTypeColumnName.FirstToUpper()));
             }
             catch (FormatException e)
             {
                 throw CreateLineParseException(lineNumber,
                                                string.Format(Resources.StructuresCharacteristicsCsvReader_ParseVarianceType_ParameterName_0_only_allows_certain_values,
-                                                             StructureFilesKeywords.VariationTypeColumnName.FirstLetterToUpper()),
+                                                             StructureFilesKeywords.VariationTypeColumnName.FirstToUpper()),
                                                e);
             }
             catch (OverflowException e)
             {
                 throw CreateLineParseException(lineNumber,
                                                string.Format(Resources.StructuresCharacteristicsCsvReader_ParseVarianceType_ParameterName_0_only_allows_certain_values,
-                                                             StructureFilesKeywords.VariationTypeColumnName.FirstLetterToUpper()),
+                                                             StructureFilesKeywords.VariationTypeColumnName.FirstToUpper()),
                                                e);
             }
         }
Index: Ringtoets/Common/src/Ringtoets.Common.IO/Structures/StructuresParameterRowsValidator.cs
===================================================================
diff -u -r5241062f8df6b7a99943ce1983ce8947adc3d899 -r24ed17047f5f34a54a707b3283d97f36e1b67f58
--- Ringtoets/Common/src/Ringtoets.Common.IO/Structures/StructuresParameterRowsValidator.cs	(.../StructuresParameterRowsValidator.cs)	(revision 5241062f8df6b7a99943ce1983ce8947adc3d899)
+++ Ringtoets/Common/src/Ringtoets.Common.IO/Structures/StructuresParameterRowsValidator.cs	(.../StructuresParameterRowsValidator.cs)	(revision 24ed17047f5f34a54a707b3283d97f36e1b67f58)
@@ -296,7 +296,7 @@
             if (double.IsNaN(value) || double.IsInfinity(value))
             {
                 messages.Add(string.Format(Resources.StructuresParameterRowsValidator_ValidateDoubleParameter_ParameterId_0_Line_1_ColumnName_2_not_number,
-                                           row.ParameterId, row.LineNumber, columnName.FirstLetterToUpper()));
+                                           row.ParameterId, row.LineNumber, columnName.FirstToUpper()));
             }
 
             return messages;
@@ -310,7 +310,7 @@
             if (double.IsNaN(value) || double.IsInfinity(value) || value < 0)
             {
                 messages.Add(string.Format(Resources.StructuresParameterRowsValidator_ValidatePositiveDoubleParameter_ParameterId_0_Line_1_ColumnName_2_must_be_a_positive_number,
-                                           row.ParameterId, row.LineNumber, columnName.FirstLetterToUpper()));
+                                           row.ParameterId, row.LineNumber, columnName.FirstToUpper()));
             }
 
             return messages;
@@ -337,7 +337,7 @@
             if (double.IsNaN(mean) || double.IsInfinity(mean) || mean <= 0 || mean > 1)
             {
                 messages.Add(string.Format(Resources.StructuresParameterRowsValidator_ProbabilityRule_ParameterId_0_Line_1_ColumnName_2_probability_out_of_range,
-                                           row.ParameterId, row.LineNumber, StructureFilesKeywords.NumericalValueColumnName.FirstLetterToUpper()));
+                                           row.ParameterId, row.LineNumber, StructureFilesKeywords.NumericalValueColumnName.FirstToUpper()));
             }
 
             return messages;
@@ -377,7 +377,7 @@
             if (type != VarianceType.StandardDeviation && type != VarianceType.CoefficientOfVariation)
             {
                 messages.Add(string.Format(Resources.StructuresParameterRowsValidator_ParameterId_0_Line_1_ColumnName_2_invalid_variancetype_value,
-                                           row.ParameterId, row.LineNumber, StructureFilesKeywords.VariationTypeColumnName.FirstLetterToUpper()));
+                                           row.ParameterId, row.LineNumber, StructureFilesKeywords.VariationTypeColumnName.FirstToUpper()));
             }
 
             messages.AddRange(ValidatePositiveDoubleParameter(row, StructureFilesKeywords.VariationValueColumnName));
@@ -388,15 +388,15 @@
                 if (row.VarianceType == VarianceType.CoefficientOfVariation && absoluteMean < valueTooCloseToZero)
                 {
                     messages.Add(string.Format(Resources.StructuresParameterRowsValidator_ParameterId_0_Line_1_ColumnName_2_mean_too_small_for_reliable_variation_value_conversion,
-                                               row.ParameterId, row.LineNumber, StructureFilesKeywords.NumericalValueColumnName.FirstLetterToUpper()));
+                                               row.ParameterId, row.LineNumber, StructureFilesKeywords.NumericalValueColumnName.FirstToUpper()));
                 }
             }
             else
             {
                 if (row.VarianceType == VarianceType.StandardDeviation && absoluteMean < valueTooCloseToZero)
                 {
                     messages.Add(string.Format(Resources.StructuresParameterRowsValidator_ParameterId_0_Line_1_ColumnName_2_mean_too_small_for_reliable_variation_value_conversion,
-                                               row.ParameterId, row.LineNumber, StructureFilesKeywords.NumericalValueColumnName.FirstLetterToUpper()));
+                                               row.ParameterId, row.LineNumber, StructureFilesKeywords.NumericalValueColumnName.FirstToUpper()));
                 }
             }
 
@@ -411,7 +411,7 @@
             if (!(orientation >= 0 && orientation <= 360))
             {
                 messages.Add(string.Format(Resources.StructuresParameterRowsValidator_ParameterId_0_Line_1_ColumnName_2_orientation_out_of_range,
-                                           row.ParameterId, row.LineNumber, StructureFilesKeywords.NumericalValueColumnName.FirstLetterToUpper()));
+                                           row.ParameterId, row.LineNumber, StructureFilesKeywords.NumericalValueColumnName.FirstToUpper()));
             }
 
             return messages;
@@ -424,7 +424,7 @@
             if (!IsValueWholeNumber(value) || value < 0)
             {
                 messages.Add(string.Format(Resources.StructuresParameterRowsValidator_ParameterId_0_Line_1_ColumnName_2_value_must_be_positive_whole_number,
-                                           row.ParameterId, row.LineNumber, StructureFilesKeywords.NumericalValueColumnName.FirstLetterToUpper()));
+                                           row.ParameterId, row.LineNumber, StructureFilesKeywords.NumericalValueColumnName.FirstToUpper()));
             }
             return messages;
         }
@@ -441,7 +441,7 @@
             if (!closingStructureInflowModelTypeRuleKeywords.Contains(value))
             {
                 messages.Add(string.Format(Resources.StructuresParameterRowsValidator_ParameterId_0_Line_1_ColumnName_2_structure_type_invalid,
-                                           row.ParameterId, row.LineNumber, StructureFilesKeywords.AlphanumericalValueColumnName.FirstLetterToUpper()));
+                                           row.ParameterId, row.LineNumber, StructureFilesKeywords.AlphanumericalValueColumnName.FirstToUpper()));
             }
             return messages;
         }
@@ -453,7 +453,7 @@
             if (!stabilityPointStructureInflowModelTypeRuleKeywords.Contains(value))
             {
                 messages.Add(string.Format(Resources.StructuresParameterRowsValidator_ParameterId_0_Line_1_ColumnName_2_structure_type_invalid,
-                                           row.ParameterId, row.LineNumber, StructureFilesKeywords.AlphanumericalValueColumnName.FirstLetterToUpper()));
+                                           row.ParameterId, row.LineNumber, StructureFilesKeywords.AlphanumericalValueColumnName.FirstToUpper()));
             }
             return messages;
         }