I’m excited to share Arcana, a RAG (Retrieval Augmented Generation) library I’ve been building for Elixir/Phoenix applications.
What is it?
Arcana lets you add vector search, document retrieval, and AI-powered Q&A to any Phoenix app. It’s designed to be embeddable - it uses your existing Ecto Repo and PostgreSQL with pgvector, no separate vector database needed.
Key Features
Simple API for basic RAG:
{:ok, doc} = Arcana.ingest("Your content", repo: MyApp.Repo)
results = Arcana.search("query", repo: MyApp.Repo, mode: :hybrid)
{:ok, answer} = Arcana.ask("What is Elixir?", repo: MyApp.Repo, llm: "openai:gpt-4o")
Agentic RAG Pipeline for complex questions:
ctx =
Agent.new("Compare Elixir and Erlang")
|> Agent.select(collections: ["elixir-docs", "erlang-docs"])
|> Agent.expand()
|> Agent.decompose()
|> Agent.search()
|> Agent.rerank(threshold: 7)
|> Agent.answer(self_correct: true)
The pipeline includes query rewriting, collection routing, query expansion, question decomposition, re-ranking, and self-correcting answers (reduces hallucinations by verifying answers are grounded in context).
Embeddings with Nx/Bumblebee:
- Local embeddings with bge-small-en-v1.5 - no API keys needed
- Or use OpenAI embeddings
- Or bring your own via the Arcana.Embedder behaviour
Pluggable Everything:
Every pipeline step has a behaviour you can implement:
defmodule MyApp.CrossEncoderReranker do
@behaviour Arcana.Agent.Reranker
@impl true
def rerank(question, chunks, opts) do
# Your cross-encoder logic
{:ok, scored_chunks}
end
end
Other highlights:
- Hybrid search (vector + fulltext with Reciprocal Rank Fusion)
- In-memory HNSWLib backend for testing or smaller apps
- Built-in telemetry for all operations
- Evaluation metrics (MRR, Recall@k, Precision@k)
- Optional LiveView dashboard
- File ingestion (text, markdown, PDF)
Links
GitHub: GitHub - georgeguimaraes/arcana: Embeddable RAG library for Elixir/Phoenix with agentic pipelines and dashboard
Hex: arcana | Hex
Demo app with Doctor Who corpus: GitHub - georgeguimaraes/arcana-adept: Example Phoenix app demonstrating Arcana RAG toolkit
Would love feedback from the community!
