Cohere Reranker

The Cohere Reranker is a postprocessor that uses the Cohere API to rerank the results of a search query.

Setup

Install the required packages:

npm

npm i @vectorstores/core @vectorstores/cohere openai

pnpm

pnpm add @vectorstores/core @vectorstores/cohere openai

yarn

yarn add @vectorstores/core @vectorstores/cohere openai

bun

bun add @vectorstores/core @vectorstores/cohere openai

You’ll need:

• OPENAI_API_KEY for generating embeddings (used to build the index)
• COHERE_API_KEY for reranking

import { CohereRerank } from "@vectorstores/cohere";
import { Document, MetadataMode, Settings, VectorStoreIndex } from "@vectorstores/core";
import { OpenAI } from "openai";

Load and index documents, then rerank retrieval results

This example follows the same flow as examples/retrieval/rerankers/CohereReranker.ts: retrieve nodes normally, then rerank them with Cohere.

async function main() {
  // ---- embeddings (required to build VectorStoreIndex)
  const openai = new OpenAI({ apiKey: process.env.OPENAI_API_KEY });
  Settings.embedFunc = async (input: string[]): Promise<number[][]> => {
    const { data } = await openai.embeddings.create({
      model: "text-embedding-3-small",
      input,
    });
    return data.map((d) => d.embedding);
  };

  // ---- load and index
  const essay =
    "Paul Graham is the cofounder of Y Combinator. He grew up in Pittsburgh...";
  const document = new Document({ text: essay, id_: "essay" });
  const index = await VectorStoreIndex.fromDocuments([document]);

  // ---- cohere reranker
  const cohereRerank = new CohereRerank({
    apiKey: process.env.COHERE_API_KEY,
    topN: 5,
    model: "rerank-v3.5",
  });

  // ---- retrieve more than the default (2)
  const retriever = index.asRetriever({
    similarityTopK: 5,
  });

  const query = "What did the author do growing up?";

  // Retrieve nodes
  const nodes = await retriever.retrieve({ query });

  // Apply Cohere reranking
  const rerankedNodes = await cohereRerank.postprocessNodes(nodes, query);

  console.log("With Cohere reranking:");
  for (const r of rerankedNodes) {
    console.log("Score:", r.score ?? "-");
    console.log(r.node.getContent(MetadataMode.NONE));
    console.log("---");
  }

  console.log("Without Cohere reranking:");
  for (const r of nodes) {
    console.log("Score:", r.score ?? "-");
    console.log(r.node.getContent(MetadataMode.NONE));
    console.log("---");
  }
}

main().catch(console.error);

API Reference

• CohereRerank