Arcana.Agent.Reranker behaviour (Arcana v1.3.3)

Behaviour for re-ranking search results.

Re-rankers improve retrieval quality by scoring chunks based on their relevance to the question, then filtering and re-sorting by score.

Built-in Implementations

Arcana.Agent.Reranker.LLM - Uses your LLM to score relevance (default)

Custom Implementations

Implement the rerank/3 callback:

defmodule MyApp.CrossEncoderReranker do
  @behaviour Arcana.Agent.Reranker

  @impl Arcana.Agent.Reranker
  def rerank(question, chunks, opts) do
    # Your custom logic
    {:ok, scored_and_filtered_chunks}
  end
end

Or provide a function directly:

Agent.rerank(ctx, reranker: fn question, chunks, opts ->
  {:ok, my_rerank(question, chunks)}
end)

Summary

Callbacks

rerank(question, chunks, opts)

Re-ranks chunks based on relevance to the question.

Callbacks

rerank(question, chunks, opts)

@callback rerank(
  question :: String.t(),
  chunks :: [map()],
  opts :: keyword()
) :: {:ok, [map()]} | {:error, term()}

Re-ranks chunks based on relevance to the question.

Returns chunks filtered by threshold and sorted by score (highest first).

Options

:threshold - Minimum score to keep (default: 7, range 0-10)
:llm - LLM function for scoring (required for LLM reranker)
:prompt - Custom prompt function fn question, chunk_text -> prompt end