Lean SEO is a dependency-free SEO layer for hand-built WordPress themes, extracted from a production WooCommerce site and generalised. It handles meta descriptions, canonicals, robots directives, Open Graph and JSON-LD in around 800 lines of PHP, configured through filters instead of an options screen, because SEO output belongs in version control rather than in the database. It also detects Yoast, Rank Math and the others on boot and stands down, so it can never emit a duplicate canonical.