The plugin version lives in .claude-plugin/plugin.json. When making changes that warrant a version bump (bug fixes, new features, behavior changes), increment the version field there before committing. Use semver patch bumps (e.g. 0.1.2 → 0.1.3) unless the change is breaking.
Do NOT add a version to .claude-plugin/marketplace.json — for URL-sourced plugins, Claude Code reads the version from plugin.json only.