How Lexiel's Legal RAG Works: Legal Research Without Hallucinations

# How Lexiel's Legal RAG Works: Legal Research Without Hallucinations

The biggest fear lawyers have when using AI is legitimate: what if it invents a judgment? Lexiel has solved this with legal RAG architecture. Here's how it works.

The Problem: LLMs Don't Know Case Law

Models like GPT-4 were trained on internet text up to a cutoff date. When you ask ChatGPT for Supreme Court judgments after 2020, it may respond with judgment numbers that look real but don't exist. This is called hallucination and is the greatest risk of using generalist AI in legal contexts.

The Solution: RAG (Retrieval-Augmented Generation)

RAG separates two functions:

1. Retrieval: searching a database of real documents for the most relevant fragments
2. Generation: using those fragments as context for the LLM to generate a response based on real data

The LLM doesn't have to invent the information, we provide it directly from verified sources.

The Corpus: 7,000+ Verified Sources

• Spain: 1,937 sources (BOE + CENDOJ: Supreme Court, Constitutional Court, National High Court), 95,244 provisions
• LATAM: Mexico, Colombia, Argentina, Chile, Peru
• Global total: 130,000+ sources, 2,300,000+ indexed provisions

The Result: 99.3% on the Official Exam

The gap between Lexiel (99.3%) and Claude without RAG (88%) is pure architecture: 7 percentage points of improvement from having the right legal corpus and hybrid search.

What Lexiel Cannot Do

• If a judgment is very recent (last 30-60 days) and not yet in the corpus, Lexiel says so clearly instead of inventing it
• The source is always shown for every statement, so lawyers can verify

Try Lexiel's legal RAG free for 14 days →