Generally speaking, the error correction website will provide a similarity report, which contains the similarity percentage of your text with other sources. The higher the percentage, the more similar your text is to other texts.
If your writing is highly similar to other sources, it may be considered plagiarism. In this case, you may need to re-examine and revise your text to ensure that it is original and conforms to relevant academic ethics.
Different websites may use different similarity detection tools and algorithms, so the exact methods may be different. It is suggested that you check the guidance or help documents provided by the error correction website when using it, understand their similarity detection methods and how to interpret the similarity report.