https://www.shortercatechism.com/

You will find commentaries/detailed catechism of below Puritans on each of shorter catechism question in this link.

• Francis R. Beattie’s The Presbyterian Standards
  • The Doctrine of the Holy Scripture
• Thomas Boston’s Of Man’s Chief End and Happiness
• James Fisher’s Catechism on the Catechism [OFFSITE]
• John Flavel’s Exposition of the Assembly’s Shorter Catechism
• Matthew Henry’s A Scripture Catechism in the Method of the Assembly’s
• Thomas Vincent’s The Shorter Catechism Explained from Scripture
• Thomas Watson’s Body of Divinity
• John Whitecross’ The Shorter Catechism Illustrated
• Alexander Whyte’s A Commentary on the Shorter Catechism