Esyllt is the Welsh form of Iseult (Isolde) — heroine of one of the great romantic tragedies of Western literature. Generally interpreted as meaning "of fair regard."
Esyllt does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Esyllt reduce to 3, The Communicator. This is a traditional interpretive system, not a factual claim about the name.