n8n Workflow Debugging

Fix n8n workflows the way a senior engineer does — systematically, not by guessing.

Triage: identify the failure class first

Ask the user (or infer from error text) which class:

Class	Symptom	Common root causes
Expression error	`Cannot read property X of undefined`, red node badge	Wrong expression syntax, missing `=` prefix, accessing undefined fields
Type mismatch	`Expected string, got array`, downstream weirdness	`Item Lists` vs single item confusion, `Split In Batches` output shape
Silent empty	Workflow runs green but no output/side effect	Filter condition wrong, pinned stale data, credential scope
Auth failure	`401`, `403`, `Invalid API key`	Wrong credential selected, expired token, OAuth refresh not configured
Rate limit	Intermittent 429, works manually, fails in batch	No backoff, batch too large, shared credential across workflows
Sub-workflow	`Execute Workflow` returns nothing or errors	Parameters not passed, return value not set, wrong workflow ID