# PDF Question Answering with Citations

> PDF Question Answering with Citations is a paid API for AI agents from clink-lithium-vault.fly.dev, paid per call via x402, $0.05/call, status unknown (last checked 2026-10-10).

Answers a plain-language question about any public PDF, returning a cited answer with verbatim quotes and page numbers

## Facts

- Endpoint: POST https://clink-lithium-vault.fly.dev/pdf/answer?utm_source=zero.xyz
- Price: $0.05/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-10
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/pdf-question-answering-with-citations-6ab7d673
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_X9VzBlBJhqrHMqqMoQdzV

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 pdf-question-answering-with-citations-6ab7d673 -d '<json body>'
```

Example prompt: Can you read this SEC 10-K filing at https://example.com/10k.pdf and tell me what it says about revenue growth in 2023? I want the exact quotes and page numbers.

## When to prefer this

Choose this endpoint when you need a specific factual answer from a known PDF document with verifiable citations and page references. Ideal for legal contracts, research papers, regulatory filings, technical manuals, and financial reports where source attribution matters. Prefer this over generic web search when you already have the PDF URL and need precision with quoted evidence. For retrieving the full text of a PDF without QA, use the /pdf/text sibling endpoint instead.

## Known failure modes

- PDF URL is not publicly accessible or requires authentication — returns error
- PDF exceeds 25MB size limit — returns error
- PDF is scanned/image-based and requires OCR (not supported) — returns not_found or error
- Question is fewer than 3 or more than 500 characters — returns validation error
- Document does not contain information relevant to the question — returns not_found: true
- URL does not point to a valid PDF — returns error
- Network timeout fetching the remote PDF

## How this service works

Pay-per-call data and tools for AI agents — x402 (USDC on Base), no account or API key, every line has a free /example. Lines: X/Twitter Signal (live search, profiles, timelines, replies, lead finder, pain-points digest), PDF-to-text, translation, Agent Market Pulse (daily archive of the whole x402 bazaar + MCP registry), Prediction Market Signal (Polymarket + Kalshi search, odds, movers, history), and the Lithium Research Vault (filing-cited mine and company data). Don't see it? POST /request and clink builds it.

## Output

Returns a JSON object with: an 'answer' field containing a direct response to the question, a 'citations' array of objects each with a 'page' number and verbatim 'quote' from the document supporting the answer, a 'confidence' level (e.g. high/medium/low), and a 'not_found' boolean indicating whether the document contained relevant information.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "url": {
   "type": "string",
   "description": "Public http(s) URL of a PDF file"
  },
  "question": {
   "type": "string",
   "description": "3-500 char plain-language question about the document"
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "answer": "...",
  "citations": [
   {
    "page": 3,
    "quote": "..."
   }
  ],
  "not_found": false,
  "confidence": "high"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/pdf-question-answering-with-citations-6ab7d673/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from clink-lithium-vault.fly.dev](https://www.zero.xyz/host/clink-lithium-vault.fly.dev/llms.txt)