Texel, by Peter Österlund, is a strong conventional engine that is best known in engine-development circles for "Texel tuning" — a method of automatically fitting evaluation parameters against game results that became standard practice across the field.
On Chessy it is here for a much more specific reason: it accepts a requested strength from −625 to 2540. Stockfish refuses to play below 1320 and silently clamps anything lower, which is why beginner bots on most chess sites are not actually beginner bots. Texel has no such floor.
It also degrades differently. Rather than running a strong search and spoiling the output, it weakens evaluation and search together, so the result plays consistently badly rather than playing well with occasional seizures. That is much closer to how a genuine beginner plays, and it is what makes Aunt Judith possible.
What makes it distinctive
- ▸Requested strength range of −625 to 2540, with no floor
- ▸Separate Strength setting from 0 to 1000, where 0 is a random mover
- ▸The engine behind Aunt Judith, the beginner bot