Reciprocal rank fusion API

Fuses multiple ranked id-lists into one ranking using Reciprocal Rank Fusion (RRF), ideal for hybrid lexical+vector search. Answers 'How do I combine multiple search rankings?', 'What is the RRF fused order?'.

Price$0.02per request

MethodPOST

Route/v1/retrieval/reciprocal-rank-fusion

StatusLive

MIME typeapplication/json

Rate limit120/minute

Cache0s public

rrffusionrank-fusionhybrid-searchrerankretrievalensemblerag

API URLhttps://x402.hexl.dev/v1/retrieval/reciprocal-rank-fusion

Integration docs

Example request

{
  "rankings": [
    [
      "a",
      "b",
      "c"
    ],
    [
      "b",
      "a",
      "d"
    ]
  ],
  "k": 60
}

Example response

{
  "k": 60,
  "listCount": 2,
  "fused": [
    {
      "id": "a",
      "rrfScore": 0.03252247
    },
    {
      "id": "b",
      "rrfScore": 0.03252247
    },
    {
      "id": "c",
      "rrfScore": 0.01587302
    },
    {
      "id": "d",
      "rrfScore": 0.01587302
    }
  ],
  "formula": "RRF(d) = Σ 1/(k + rank_i(d))"
}

Input schema

{
  "type": "object",
  "required": [
    "rankings"
  ],
  "properties": {
    "rankings": {
      "type": "array",
      "items": {
        "type": "array"
      }
    },
    "k": {
      "type": "number"
    }
  }
}

Output schema

{
  "type": "object",
  "additionalProperties": true
}