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PDF Question Answering with Citations
x402
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
Price / call$0.05
Success—
StatusUnknown
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.
Example use cases
Contract clause lookup
“Here's a PDF of our vendor contract at https://contracts.example.com/vendor_agreement.pdf — what does it say about termination notice periods? Give me the exact wording and which page it's on.”
Research paper fact extraction
“I've got this academic paper at https://arxiv.org/pdf/2401.12345.pdf — what accuracy did the model achieve on the ImageNet benchmark? I need the specific number with the quote from the paper.”
Regulatory filing question
“Can you check the FDA guidance document at https://fda.gov/docs/guidance.pdf and tell me whether it covers post-market surveillance requirements for Class II devices?”
Technical details
Endpoint
POSThttps://clink-lithium-vault.fly.dev/pdf/answer?utm_source=zero.xyzWhen to prefer
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.
Side effects
- 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
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| url | string | Public http(s) URL of a PDF file |
| question | string | 3-500 char plain-language question about the document |
Output
Schema · Response
{
"type": "json",
"example": {
"answer": "...",
"citations": [
{
"page": 3,
"quote": "..."
}
],
"not_found": false,
"confidence": "high"
}
}Tags
x402
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