What is the hardest palindrome?

The hardest palindrome can vary depending on the criteria used, but one of the most complex examples is the Finnish Word "saippuakivikauppias," meaning "soapstone vendor." This 19-letter palindrome is notable for its length and linguistic complexity. Palindromes can also be challenging in terms of creating long phrases or sentences that read the same forwards and backwards, but they typically require more creative constraints.