How it works
Hexadecimal text represents each byte with two base-sixteen digits. It is useful for displaying a small binary payload, a test vector, or a diagnostic identifier in a form that can be copied and compared. The representation is text, while the underlying data remains a sequence of bytes. Converting between the two should preserve every byte, including zero values and leading zero digits.
Convert.ToHexString and Convert.FromHexString provide a direct round trip for this representation. They do not interpret the bytes as UTF-8 text, a signed integer, or a platform-specific binary structure. Those would be additional contracts layered on top of the byte sequence. Keeping the layers distinct prevents a convenient debugging representation from being mistaken for a complete serialization format.
Walk through the example. The input text contains three byte pairs: zero, fifteen, and two hundred fifty-five. Decoding it creates a three-byte array. The program prints those numeric byte values, then encodes them back to uppercase hexadecimal. The final comparison confirms that a separately prepared byte array has the same contents, using SequenceEqual rather than reference equality.
Watch the boundary. A valid hexadecimal string needs a valid digit in every position and a complete pair for each byte. Malformed or odd-length text is not a partial successful result. Also do not use BitConverter output without specifying byte order when bytes represent larger numbers in a shared format; hexadecimal formatting alone does not define an integer's endianness or signedness.
Practice independently. Encode a prepared four-byte message to hexadecimal and decode it back. Test a leading zero byte, all-zero input, an invalid letter, and an odd number of digits. Define whether an empty payload is valid. Then design a two-byte unsigned integer format with an explicit byte order and explain which extra rule turns the same raw bytes into a numeric value.
A working example
using System;
using System.Collections.Generic;
using System.Linq;
using System.Globalization;
using System.Text;
using System.Text.Json;
using System.Text.Json.Serialization;
using System.Text.RegularExpressions;
byte[] bytes = Convert.FromHexString("000FFF");
Console.WriteLine(bytes.Length);
Console.WriteLine(string.Join(",", bytes));
Console.WriteLine(Convert.ToHexString(bytes));
Console.WriteLine(bytes.SequenceEqual(new byte[] { 0, 15, 255 }));
Expected output
3 0,15,255 000FFF True
Hex text represents bytes; numeric interpretation still needs an explicit byte-order contract.