Built-in Providers

Lucerna ships several embedding and reranking providers. You can select them with CLI flags (no config file needed) or instantiate them in lucerna.config.ts.

Embedders

Pass --embedder <name> to any command, or use new ProviderClass() in your config file:

Name	Class	Notes
cloudflare	CloudflareEmbeddings	Requires CLOUDFLARE_ACCOUNT_ID + CLOUDFLARE_API_TOKEN
local / hf	HFEmbeddings	Local ONNX via @huggingface/transformers, no API key
bge-small	BGESmallEmbeddings	Local BGE-small model
nomic	NomicCodeEmbeddings	Local Nomic code model (default when no env vars set)

Via CLI flag

lucerna mcp-server /path/to/project --embedder cloudflare
lucerna index /path/to/project --embedder local

Via config file

lucerna.config.ts

import { CloudflareEmbeddings } from '@upstart.gg/lucerna';

export default {
  embeddingFunction: new CloudflareEmbeddings(),
};

Disable semantic search

lucerna mcp-server /path/to/project --no-semantic   # BM25 only

Rerankers

Pass --reranker <name> or use new RerankerClass() in your config:

Name	Class	Notes
cloudflare	CloudflareReranker	Requires CLOUDFLARE_ACCOUNT_ID + CLOUDFLARE_API_TOKEN
jina	JinaReranker	Requires JINA_API_KEY
voyage	VoyageReranker	Requires VOYAGE_API_KEY

Via CLI flag

lucerna mcp-server /path/to/project --reranker voyage
lucerna search /path/to/project "auth middleware" --reranker jina

Via config file

lucerna.config.ts

import { VoyageReranker } from '@upstart.gg/lucerna';

export default {
  rerankingFunction: new VoyageReranker(),
};

Combining embedder + reranker

lucerna mcp-server /path/to/project \
  --embedder cloudflare \
  --reranker voyage

Or in lucerna.config.ts:

import { CloudflareEmbeddings, VoyageReranker } from '@upstart.gg/lucerna';

export default {
  embeddingFunction: new CloudflareEmbeddings(),
  rerankingFunction: new VoyageReranker(),
};