Should I use multiple AI tools (ChatGPT, Gemini, Grok, Claude) to optimize my resume?

You don't need to. One well-trained tool is more efficient. Claude is recommended — start a project, give it your base resume, a job description, and prompt it to optimize keywords for the ATS while keeping everything truthful. Ask it to flag gaps and missing skills. Once you've validated the output a few times, you'll trust the data and can do this in about five minutes per application.