This study explores the efficacy of ChatGPT-3.5, an AI chatbot, used as an Automatic Essay Scoring (AES) system and feedback provider for IELTS essay preparation. It investigates the alignment between scores given by ChatGPT-3.5 and those assigned by official IELTS examiners to establish its reliability as an AES. It also identifies the strategies employed by ChatGPT-3.5 in revising essays based on the four IELTS rubrics: task achievement, coherence and cohesion, lexical resources, and grammatical range and accuracy. Based on pre-rated essays from an official IELTS preparatory book as a control measure to ensure objectivity, the findings indicate a discrepancy, with ChatGPT-3.5 typically assigning lower scores compared to official raters. However, ChatGPT-3.5 shows a robust capability to revise essays across all four descriptors. In addition, the effectiveness of ChatGPT-3.5 as a feedback provider may be attributed to the essay type and its widely accepted rubrics. Our study contributes to the understanding of the application of AI tools in second language writing and suggests that future studies should focus on evaluating the capacity and effectiveness of such tools in pedagogical applications.