A field guide to good gems, by layer

Layered
Rails Gems

Every gem that Layered Design for Ruby on Rails Applications, Second Edition flags as a good tool — the formal “What a gem” callouts and the inline recommendations — mapped to the architectural layer it belongs to, each with a book page reference and a minimal usage sketch.

Second Edition Dec 2025 Packt 13 layers 70 gems
70 gems

What made the cut

Formal “What a gem” callouts plus gems the book actively recommends or reaches for in its examples. Left out on purpose: cautionary examples (a DSL shown as a query pitfall, schedulers shown as an anti-pattern), pure framework plumbing described in passing, and libraries named only to illustrate a category rather than endorse it.

36 “What a gem” callouts
~ 34 inline recommendations
across 13 layers, chapters 1–15

No gems match . Try another layer or clear the search.