# Book402 Hybrid Book Search

> Book402 Hybrid Book Search is a paid API for AI agents from book402.com, paid per call via x402, $0.01/call, status unknown (last checked 2026-09-14).

Performs hybrid BM25+vector search across 3,807 books, returning ranked results with titles, authors, genres, and relevance scores

## Facts

- Endpoint: GET https://book402.com/search/hybrid
- Price: $0.01/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/book402-hybrid-book-search-79ae16f3
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_peLFcgS7n3xZS-Of2lwpB

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability book402-hybrid-book-search-79ae16f3
```

Example prompt: Search Book402's library of 3,807 books for titles about stoicism and return the top 5 results with authors, genres, and relevance scores.

## When to prefer this

Use this endpoint when you need to discover books by topic, concept, theme, or author using natural language queries. The hybrid BM25+vector approach makes it better than pure keyword search for semantic queries like 'books about inner peace' or 'Stoic philosophy'. Prefer this over full-text passage search when you want book-level discovery rather than specific excerpts.

## Known failure modes

- Missing required 'q' parameter returns a 400 or validation error
- Empty or overly generic query may return low-relevance results with low scores
- Limit parameter exceeding allowed max may be clamped or rejected
- Payment not sent or insufficient USDC triggers a 402 Payment Required response
- Network timeout if the backend search index is temporarily unavailable

## How this service works

Hybrid BM25+vector search across 3,807 books. Returns ranked results with titles, authors, genres, and relevance scores. Query param: q (string, required) - search query, limit (number, optional, default 20). Example: GET /search/hybrid?q=stoicism. Returns JSON array of matching books.

## Output

A JSON array of matching books, each with an id, title, author, genre, and a relevance score (float). Results are ranked by combined BM25 and vector similarity. The total count of matches is also returned.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [
      "q"
     ],
     "properties": {
      "q": {
       "type": "string",
       "description": "Search query"
      },
      "limit": {
       "type": "string",
       "description": "Max results"
      }
     }
    }
   }
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "total": 1,
  "results": [
   {
    "id": 42,
    "genre": "Philosophy",
    "score": 0.95,
    "title": "Meditations",
    "author": "Marcus Aurelius"
   }
  ]
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/book402-hybrid-book-search-79ae16f3/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from book402.com](https://www.zero.xyz/host/book402.com/llms.txt)