Begin learning the right way to write grammatically correct sentences and you won't need automated tools.
"Why was the road crossed by the chicken?"
The sentence is poorly constructed as to subject and predicate. The chicken should be the subject. The chicken crossed the road. Roads cannot be active, therefore you can't write an active sentence about a road, unless the road happens to be in a fairy tale.
"Why did the chicken cross the road is an active sentence?"
A major problem with grammar checkers is that they "green squiggle" anything that their algorithms flag as a mistake. For instance, the sentence "The road was less traveled than the highway," would be flagged for several reasons. First, it is passive; next to be correct it should read "the highway was traveled", but in the vernacular that makes the sentence stiff and strange.
If you know you are writing a passive sentence or making a grammatical error, it you know your reason for doing so and it's a good one, go for it. That's something a grammar checker won't normally tell you -- no matter how good it is -- but something that writers who have a good grasp of their mechanics know.