Prerequisites

A prerequisite is a skill you need before another skill becomes learnable. You can't write media queries before you know CSS basics; you can't run an email campaign before you can write one email. Prerequisites are how the forest knows the order of things — they're the arrows on the map.

Two rules make prerequisites work, and both are about defining things once.

Prerequisites live on the skill itself. They're defined once, at the organisation level — not inside any particular tree. A tree only shows a grouping of skills; the connections between those skills already exist on the skills themselves. So if two connected skills are both pulled into a tree, they arrive already linked. Define the connection once, and every tree that ever shows those skills agrees about it.

No double-linking. If B depends on A, and C depends on B, then C connects through B — never also directly back to A. The chain A → B → C already says everything; an extra A → C arrow adds clutter without adding information. Keeping chains clean is what keeps a tree readable at a glance.

A skill can have several prerequisites and can unlock many skills — chains branch and merge. That's normal and healthy; it's what makes the map look like a tree instead of a ladder.