StringExtension

A string manipulation library for C#, built around three principles: correctness, performance, and a minimal API surface.

• Zero-allocation where possible. Most methods operate on Span<char>/ReadOnlySpan<char> internally, using stackalloc for small inputs and ArrayPool<char> for larger ones instead of allocating a new array on every call.
• Unicode-correct. Methods that classify or compare characters operate on whole Unicode scalar values (via Rune) rather than raw UTF-16 code units, so characters outside the Basic Multilingual Plane (many emoji, some rare scripts) are handled correctly instead of being split into invalid half-characters.
• Both string and ReadOnlySpan<char> overloads. Every method that accepts a string also has a ReadOnlySpan<char> overload, so you can call it on a slice without allocating an intermediate string.

Requirements

.NET 10.0 or later.

Installation

dotnet add package String-Extension

API

Methods are split across namespaces by category. Add the relevant using statement for the methods you need.

using StringExtension;

General-purpose string manipulation.

Method	Description
RemoveCharacters(char[])	Removes the specified characters from a string.
CountSubstring(string)	Counts the number of occurrences of a substring.
ReverseWords()	Reverses the order of words in a string.
RemoveDuplicateCharacters()	Removes duplicate characters, keeping the first occurrence of each.

using StringExtension.Validation;

Format validation.

Method	Description
IsValidEmail()	Validates an e-mail address.
IsValidPhoneNumber()	Validates a phone number.

using StringExtension.Linguistics;

Text analysis.

Method	Description
IsPalindrome()	Determines if a string is a palindrome.
CountLetters()	Counts the number of letters in a string.

using StringExtension.Casing;

Casing conventions and slug generation.

Method	Description
ToCamelCase()	Converts to camelCase.
ToPascalCase()	Converts to PascalCase.
ToSnakeCase()	Converts to snake_case.
ToKebabCase()	Converts to kebab-case.
ToTitleCase(bool)	Converts to Title Case, with an optional flag to keep short English words (of, the, and, ...) lowercase.
Slugify(char)	Converts to a URL-friendly slug, stripping accents and collapsing punctuation into a single separator.

Examples

using StringExtension;
using StringExtension.Casing;
using StringExtension.Linguistics;
using StringExtension.Validation;

"hello world!".RemoveCharacters(['l', 'o']);   // "he wrd!"
"hello world!".ReverseWords();                 // "world! hello"

"john.doe@example.com".IsValidEmail();         // true
"racecar".IsPalindrome();                      // true

"hello_world".ToCamelCase();                   // "helloWorld"
"helloWorld".ToSnakeCase();                    // "hello_world"
"the lord of the rings".ToTitleCase(useEnglishMinorWordRules: true);
                                                // "The Lord of the Rings"
"Café de la Gare! 2024".Slugify();             // "cafe-de-la-gare-2024"

Performance

Every method that returns a string avoids unnecessary intermediate allocations. As an example, here is the impact of the zero-allocation rewrite of a few methods (measured with BenchmarkDotNet on identical hardware, before and after):

Method	Before	After	Allocated (before → after)
IsPalindrome	466 ns	1.6 ns	648 B → 0 B
CountSubstring	59 ns	1.6 ns	40 B → 0 B
CountLetters	101 ns	3.7 ns	32 B → 0 B

Run the benchmarks yourself:

dotnet run -c Release --project Benchmarks/Benchmarks.csproj

Tests

• Unit tests: UnitTests/StringExtensionTests.cs
• Performance tests: Benchmarks/Benchmark.cs

dotnet test

Contributing

Contributions are welcome, whether that's proposing new methods, reporting bugs, or improving existing code. Open a Pull Request and it will be reviewed.

License

Distributed under the MIT License. See LICENSE for details.