A skill is a named set of instructions Claude can call on, stored in a SKILL.md file. Claude can propose new skills or improvements to existing ones. The rule that Claude must read a skill before replacing it used to cover only improvements aimed at a named skill.
It now also covers new proposals that share a name with one of your own skills, or with a skill whose owner is unknown. Such a proposal is refused unless Claude has read that skill's SKILL.md in full and the file has not changed since. Names count as the same even with a leading slash, an anthropic-skills: or claude-ai: prefix, or small differences in characters and hyphens.
The check also runs again at the moment the proposal is made. If a lookup fails, the proposal is no longer let through.
Claude can no longer quietly overwrite one of your existing skills by proposing a "new" one with the same name, since saving it would replace the old SKILL.md entirely.
Whether the skill-proposing tool itself is only available to some accounts is not stated.