Structure rule catalog

The 5 rules lintStructure ships. Each rule lives in packages/quality/src/structure/rules/; severity is user-overridable per Options.

Tree integrity

Rule	Default severity	Auto-fix	What it checks
structure.duplicate-block-id	error	—	Two or more blocks share the same id. Tree traversal, undo/redo, selection, and every block-by-ID operation rely on uniqueness; a duplicate corrupts them silently. Usually a sign of a broken import or a clone path that forgot to regenerate IDs.
structure.nested-section	error	—	A section block sits inside another section's column. The renderer rejects this — sections cannot nest — so the inner section silently drops out of the MJML output. Catches importer bugs and copy-paste accidents.

Section layout

Rule	Default severity	Auto-fix	What it checks
structure.section-column-mismatch	error	—	The section's columns value implies a column count that doesn't match children.length. "1" expects 1 inner array, "2"/"2-1"/"1-2" expect 2, "3" expects 3. A mismatch means either the layout key or the children array is wrong — both yield broken render output. The editor's section toolbar rebalances children automatically when the layout changes; this rule catches data that bypassed the toolbar (imports, manual JSON edits, stale snapshots).

Content presence

Rule	Default severity	Auto-fix	What it checks
structure.empty-section	warning	yes	A section has no columns, or every column is empty. Renders as a blank table row in most clients — wasted whitespace and an occasional visible padding gap. Auto-fix removes the section.
structure.empty-column	warning	—	A multi-column section has at least one column with no blocks. Renders awkwardly (uneven gaps, collapsed columns on mobile) and almost always means the author intended fewer columns. No auto-fix because the right answer (merge into a sibling vs. drop the section vs. change the columns layout) depends on intent.