No. grammar checker does a spelling and grammar check based on the dictionaries and grammar rules that have been programmed into it. If a user rights some sentences or a rhyme which is nonsensical but contain no spelling or grammar mistakes, the spelling and grammar check routines will not flag them as errors. There are so many examples in the English language where renowned writers have written essays, books, and children's rhymes which don’t make any sense. But they don't contain any spelling or grammar mistakes. For example, Dr. Seuss famous line 'Do you like green eggs and ham?' sounds meaningless but does not contain any spelling or grammar mistakes. Therefore, any spelling and grammar check tool will not flag it as being wrong.
Grammar checker does the grammar check, and if a text does not contain any grammar errors, it will not display any flags. Users who are familiar with the English language and use a grammar check tool to check errors know that some sentences can be written which will not be flagged as containing spelling or grammar mistakes.
Errors can occur if: the error is not contained in grammar checker's database of texts; the grammar is alright but unintelligible; the error is sporadic; the error is extremely complex and not catered for by grammar checker. In such scenarios, any grammar check tool will not point out grammar errors. Even the websites that claim to be the best grammar checker application available will not point out mental and rare mistakes.
Grammar checker may be one of the best grammar checker tools available right now, but there are certain errors it will not flag. Therefore, you must review your work before you accept it to be 100% error free. Human intervention is required to ensure that text is error-free.