n8n-structured-extraction

n8n Structured Extraction (JSON-schema-driven)

For ANY structured output (extraction, classification) use a dedicated structured node with a real JSON schema — never an AI-Agent node with a "return JSON" prompt, never tolerant re-parsing of raw text. This is state-of-the-art LLM document extraction, proven in production (supplier-check and invoice-extraction pipelines).

Use the right node

Task	Node	Output
Pull fields out of a document/text	@n8n/n8n-nodes-langchain.informationExtractor	one object matching your schema
Route input into categories	@n8n/n8n-nodes-langchain.textClassifier	one output branch per category

Why NOT an AI-Agent + "give me JSON"

Agent (Tools Agent) + outputParserStructured + reasoning models (gpt-5.x) fail reproducibly:

• the model wraps the result in {"output": {...}} → top-level schema mismatch,
• and violates enums ("verlängert" instead of the schema's "verlaengert").

Prompt-only JSON is fragile. The Information-Extractor / Text-Classifier nodes use the model's native structured-output / function-calling and enforce the schema cleanly.

How to apply

Every schema field gets a type AND a description. The description is an instruction to the model (format hints), not decoration. Types must match the downstream sink (e.g. DataTable column types: number↔number, string↔string). Use real umlauts (ä, ö, ü, ß) in descriptions — never ASCII transcriptions.

// Information Extractor — manual JSON schema (nested arrays OK)
{
  "type": "object",
  "properties": {
    "rechnungsnummer": { "type": "string",  "description": "Rechnungs-/Belegnummer wie auf dem Dokument" },
    "rechnungsdatum":  { "type": "string",  "description": "Rechnungsdatum als ISO-Datum, z.B. 2026-05-29" },
    "nettobetrag":     { "type": "number",  "description": "Nettobetrag in EUR, nur Zahl ohne Währungssymbol" },
    "steuersatz":      { "type": "number",  "description": "Umsatzsteuersatz in Prozent, z.B. 19" },
    "ev_typ":          { "type": "string",  "enum": ["einfach", "erweitert", "verlaengert"],
                         "description": "Art des Eigentumsvorbehalts. ASCII-Enum-Werte exakt verwenden." },
    "positionen": {
      "type": "array",
      "description": "Einzelpositionen der Rechnung",
      "items": {
        "type": "object",
        "properties": {
          "bezeichnung": { "type": "string", "description": "Artikel-/Leistungsbezeichnung" },
          "betrag":      { "type": "number", "description": "Positionsbetrag netto in EUR" }
        }
      }
    }
  }
}