Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the burden. It discloses that the tool is read-only and lists built-in matrices, which implies no mutation. However, it doesn't describe the return format, whether the list is exhaustive, or whether it reflects the current Aseprite version. For a simple list tool, this is adequate but not rich.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.