Web answer

AI-generated answer to a natural-language question, grounded in live web search results with source citations. Send GET /api/answer with the required field q and pay $0.08 per call over x402 or MPP (there is no free tier). It returns a JSON object with query, answer, citations and citationCount.

Returns clean prose plus a structured citations array (URL, snippet, favicon) - backed by an independent search index, not the model's training data. Useful when an agent needs a synthesized answer plus the receipts to verify or follow up.

Category: Web & documents · Tags: search answer ai rag citations research fresh-data

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Parameters

Example request

curl -i "https://agent402.tools/api/answer?q=what+is+the+x402+payment+protocol%3F"

Without payment this returns HTTP 402 Payment Required with the exact price for answer; any x402 v2 or MPP client pays it and retries.

Example response

{
  "query": "what is the x402 payment protocol?",
  "answer": "x402 is an open standard for internet-native, pay-per-request HTTP APIs that uses the HTTP 402 \"Payment Required\" status code to negotiate and settle micro-payments inline with the original request.",
  "citations": [
    {
      "url": "https://www.x402.org/",
      "snippet": "x402: An open standard for internet-native payments.",
      "favicon": "https://imgs.search.brave.com/...",
      "number": 1
    }
  ],
  "citationCount": 1
}

From an MCP client

catalog.call {
  "slug": "answer",
  "params": {
    "q": "what is the x402 payment protocol?"
  }
}

The hosted connector at https://agent402.tools/mcp needs a payment for answer; the stdio package pays it from a wallet or from AGENT402_CREDITS_KEY. Local install: npx -y agent402-mcp.

Errors and behavior

• q is required. An input the tool rejects returns an HTTP 4xx whose body carries error, tool, expected, required and example, so the caller can correct it.
• A paid call that ends in any status of 400 or above is not charged over x402, MPP or a prepaid credits key: settlement is cancelled when the tool fails. The exception is a Tempo push credential, a transfer the buyer sent before the call: it settles before the tool runs, so if the tool then fails the payment is recorded as a refund owed to the paying wallet.
• Wallet-only: this tool runs a model, so it has no proof-of-work tier. A prepaid card-credits key issued earlier (Authorization: Bearer a402_...) also pays it.
• Model-backed: the answer is generated by a model, so the same input can produce different wording.
• A POST with a JSON body to /api/answer is served as this GET, with the body as the input.
• An Idempotency-Key header makes a retried paid call replay the first 200 instead of charging again (an answer larger than 1 MB is not replayed).

Paid call (JavaScript agent)

import { wrapFetchWithPayment } from "@x402/fetch";
import { x402Client } from "@x402/core/client";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

const client = new x402Client();
client.setSpendControls?.(false); // keep your own spending ceiling in code
registerExactEvmScheme(client, { signer: privateKeyToAccount(KEY) });
const payFetch = wrapFetchWithPayment(fetch, client);

const res = await payFetch("https://agent402.tools/api/answer?q=what+is+the+x402+payment+protocol%3F");

Part of these workflows

Web answer is one step in these 2 skill packs, each sold as a single call:

• Answer-a-question with sources - The 'research a question, return an answer with citations' workflow. Brave answer for the AI-synthesized take with citations, Brave web for the canonical SERP, Brave news for time-sensitive context, then a deterministic web-fetch + extract pass on the top citations to verify the answer hasn't hallucinated. Five tools, one cited paragraph, every claim traced back to a fetched URL.
• Article digest - Quick research brief on any topic - web search results plus an AI-generated answer in one pass.

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