It spans keyword placement in titles and bullets, backend search terms, image compliance, and — increasingly important — pre-launch compliance checks so the listing isn't suppressed. Pick a tool by which of these you lack.
Some tools give you fill-in templates; others (like ListingGood) write the title, bullets, and description with AI and then compliance-check them. AI writing saves the most time for sellers with many SKUs.
Most 'optimization' tools ignore compliance. If takedowns cost you sales, prioritize a tool with a free pre-launch check and POA drafting (ListingGood).
Entry plans range from free (limited) to ~$39–$99/mo. ListingGood's free scan plus a low star-based monthly plan is the cheapest way to get compliance + AI writing.