n8n LangChain Integration: Complete RAG Workflow Tutorial

Retrieval-Augmented Generation (RAG) in n8n combines the reasoning power of Large Language Models (LLMs) with your private data stored in vector databases. Unlike standard chatbots that hallucinate, an n8n RAG pipeline retrieves exact context from your documents before answering, ensuring high accuracy for enterprise applications.

In 2026, building a chatbot is easy. Building a reliable domain expert that references your internal Notion pages, PDFs, and SQL databases without hallucinating is the real engineering challenge.

While Python frameworks like LangChain offer infinite flexibility, they require heavy maintenance. n8n has bridged this gap with its LangChain Integration, allowing you to visually orchestrate RAG pipelines while retaining the ability to drop into code for custom logic.

This tutorial is a technical deep dive into building production-grade n8n RAG workflows. We will move beyond basic "PDF chat" examples to construct an enterprise Q&A system with observability, error handling, and multi-step reasoning.

What is RAG in n8n?

Retrieval-Augmented Generation (RAG) is an architectural pattern that optimizes LLM output by referencing an authoritative knowledge base outside its training data.

In n8n, you don't just "connect an LLM." You build a chain—a sequence of logic where:

1. Retrieval: The system fetches relevant chunks from a vector database (Pinecone, Supabase, Weaviate).

2. Augmentation: These chunks are injected into the system prompt as context.

3. Generation: The LLM (GPT-4o, Claude 3.5) generates an answer based only on that context.

Why n8n + LangChain?

Standalone LangChain scripts are powerful but opaque. n8n visualizes the flow. You can see exactly where the retrieval failed, inspect the JSON chunks returned from your vector store, and retry specific nodes.

The LangChain Code Node vs. Standard AI Agent

• Standard AI Agent: Great for general tasks (e.g., "Take this text and summarize it"). It hides the complexity of the chain.

• LangChain Code Node: This gives you raw access to the LangChain JS library. You can define custom Tools, write complex OutputParsers, or implement experimental retrieval strategies (like Parent Document Retrieval) that aren't yet available as drag-and-drop nodes.

Prerequisites

To follow this tutorial, you need a robust environment.

• n8n Version: v1.80.0 or higher (Self-hosted on Docker is recommended to enable full LangChain filesystem access).

• Vector Database:

  • Pinecone: Best for managed, serverless scaling.

  • Supabase (pgvector): Best if you already use Postgres; offers hybrid search.

• LLM Provider:

  • Anthropic Claude 3.5 Sonnet: Superior reasoning for complex retrieval.

  • OpenAI GPT-4o-mini: Cost-effective for simple queries.

• Embeddings Model: text-embedding-3-small (OpenAI) or cohere-embed-v3 (for better multilingual support).

Step 1: Document Ingestion Pipeline

Before you can search, you must index. We will build a workflow that runs nightly to sync your company's knowledge base.

[Diagram: Workflow showing "Schedule Trigger" -> "Notion Node" -> "Text Splitter" -> "Embeddings" -> "Pinecone"]

1. Load Documents

Use the Notion node (or Google Drive/PDF Loader).

• Resource: Database

• Operation: Get Many

• Return All: True

• Key Tip: Don't just load the body text. Map metadata like url, author, and last_edited to the output. This metadata is crucial for filtering later.

2. Split Text into Chunks

Raw text is too large for an LLM's context window. Use the Recursive Character Text Splitter node.

• Chunk Size: 500 characters.

• Overlap: 50 characters.

• Why? Overlap ensures that context isn't lost if a sentence is cut in the middle.

3. Generate Embeddings & Store

Connect the Embeddings OpenAI node to a Pinecone Vector Store node.

• Operation: Insert Documents.

• Mode: Upsert (Update if exists).

• Critical: Use a consistent ID generation strategy (e.g., MD5(url)) to prevent duplicate entries when you re-run the ingestion.

Step 2: Query Pipeline (RAG Core)

This is the workflow that runs when a user asks a question via Slack or a Chatbot.

1. The Vector Store Retriever

Instead of a standard node, we use the Vector Store Retriever. This is a sub-node that connects to your Retrieval QA Chain.

• Search Type: Similarity.

• Top K: 4 (Retrieve the 4 most relevant chunks).

2. Semantic Search Configuration

In the Pinecone node attached to the retriever:

• Metadata Filter: { "status": "published" } (Ensure you don't retrieve draft documents).

3. LangChain Prompt Template

Standard prompts are weak. Use a robust template in the Retrieval QA Chain node:

Markdown

You are a technical support engineer for Chronexa.
Use the following pieces of context to answer the user's question.
If the context does not contain the answer, say "I don't have that information in my knowledge base."

CONTEXT:
{{ $json.context }}

QUESTION:
{{ $json.question }}

ANSWER:

4. LLM Connection

Connect OpenAI Chat Model (GPT-4o).

• Temperature: 0.1. (Low temperature is vital for RAG; you want facts, not creativity).

Step 3: Advanced RAG Patterns

Basic RAG fails when the user asks vague questions. Here is how to make it "Smart" using n8n LangChain advanced patterns.

Multi-Query Retrieval

A user might ask, "How do I fix the billing error?" This is vague.

Use a LangChain Code Node to generate three variations of the question before retrieval:

1. "Troubleshooting billing API 400 errors"

2. "Credit card declined error handling"

3. "Invoice generation failure steps"

Then, retrieve documents for all three and deduplicate the results. This increases the hit rate significantly.

Re-ranking with Cohere

Vector similarity isn't perfect. It finds text that looks similar, not necessarily text that answers the question.

• Pattern: Retrieve 20 documents (Top K=20).

• Step: Pass them through a Code Node that calls the Cohere Rerank API.

• Result: Take the top 5 from Cohere. This "second opinion" filters out irrelevant matches that just happened to share keywords.

Hybrid Search (Keyword + Semantic)

Pure vectors miss exact part numbers (e.g., "Error 5053").

• Use Supabase or Weaviate nodes which support Hybrid Search.

• This combines BM25 (keyword matching) with Cosine Similarity (meaning matching) for the best of both worlds.

Step 4: Production Features

An n8n LangChain pipeline isn't production-ready until it's observable.

LangSmith Monitoring Setup

Debugging a chain is hard. Did the retrieval fail? Or did the LLM ignore the context?

Integration is native in self-hosted n8n. Set these environment variables:

export LANGCHAIN_TRACING_V2=true
export LANGCHAIN_ENDPOINT="https://api.smith.langchain.com"
export LANGCHAIN_API_KEY="ls__..."
export LANGCHAIN_PROJECT="n8n-production-rag"

Once active, every execution in n8n sends a trace to LangSmith, showing you the exact inputs and outputs of every step in the chain.

Cost Tracking

Create a generic Postgres node at the end of your workflow to log usage:

• query_text

• response_time_ms

• tokens_used (Available in the output JSON of the OpenAI node).

• cost_estimate ($0.005 per query).

Full Workflow: Enterprise Q&A System

Let's assemble the pieces into a cohesive architecture.

[Diagram: User (Slack) -> Webhook -> n8n -> Moderator (LLM) -> RAG Chain -> Slack Reply]

1. Input: User posts in #ask-engineering on Slack.

2. Moderation: A fast GPT-4o-mini node checks if the question is safe and relevant.

3. Routing: If the question is about "HR", route to the HR Vector Store. If "Code", route to the GitHub Vector Store.

4. Retrieval: The RAG Chain executes.

5. Validation: The LLM's answer is checked. Does it contain "I don't know"? If so, tag a human engineer in Slack.

6. Output: The final answer is formatted in Slack Block Kit and posted as a thread reply.

Performance Metrics:

• Latency: ~3.5 seconds.

• Accuracy: 92% on technical documentation queries.

• Cost: ~$0.02 per query (using GPT-4o for the final synthesis).

Code Node Deep Dive (Advanced)

For the developers reading this, the LangChain Code Node is your escape hatch. When the drag-and-drop nodes aren't enough, you can write JavaScript that interacts directly with the chain.

Example: Custom JSON Output Parser

You need the LLM to return strictly formatted JSON for an API payload.

JavaScript

// Inside a LangChain Code Node
const { StructuredOutputParser } = require("langchain/output_parsers");

const parser = StructuredOutputParser.fromNamesAndDescriptions({
    answer: "The answer to the user's question",
    source_id: "The ID of the document used",
    confidence: "A rating between 0 and 1"
});

const formatInstructions = parser.getFormatInstructions();

// Inject 'formatInstructions' into your prompt context
return { formatInstructions };

Troubleshooting Common Issues

Vector DB Connection Failures

• Symptom: "Connection timed out" or "Dimension mismatch".

• Fix: Ensure your embedding model dimensions match your index. text-embedding-3-small is 1536 dimensions. If you created a Pinecone index with 768 dimensions (for HuggingFace models), it will fail.

High Token Costs

• Symptom: RAG pipeline costs $5/day for 10 users.

• Fix: Your chunks are too big. Reduce Chunk Size to 500 characters. You are likely feeding the LLM 3,000 tokens of context to answer a "Yes/No" question.

"I don't know" Loops

• Symptom: The LLM refuses to answer even with context.

• Fix: Check your retrieval distance metric. If using Cosine Distance, ensure your threshold isn't too strict (e.g., asking for >0.9 similarity). Lower it to 0.75.

Vector Database Comparison

Conclusion

The n8n LangChain integration has shifted the paradigm. You no longer need a dedicated backend team to build enterprise-grade AI. You need a workflow.

By combining the visual observability of n8n with the raw power of LangChain's code capabilities, you can build RAG pipelines that are not just "demos," but critical business infrastructure. Start with the ingestion pipeline, master the retrieval prompts, and use LangSmith to ensure you aren't flying blind.

Need enterprise RAG pipelines? Chronexa.io builds production n8n + LangChain systems with monitoring. Book a free scoping call.