Synonym substitution is a real technique with a narrow, honest use. Here is where it helps, where it produces word salad, and why rewriting to dodge a detector does not work.

The honest answer is that length is an output, not a target. Here is what the correlation studies actually show, the limits worth counting to, and how to use reading time well.

What an automated spell checker is genuinely good at, what it reliably misses, and how to build a five-minute proofreading pass around it that actually works.

A spell checker flags words that are not words. It cannot flag a real word used in the wrong place, which is where almost every published error comes from.