What are the limitations of using readily available online DDoS tools?

Online DDoS tools often have limitations. They may lack sophistication compared to custom-built attacks. They can be detected and mitigated more easily by security systems. The effectiveness of the tool depends on the size and quality of the underlying botnet. Many tools also come with a high risk of being flagged as malicious and blocked by ISPs and security providers. Furthermore, the tools may not be reliable or provide adequate support.