Exa grounded answer

Ask a question and get a written answer with the sources it was drawn from. Send POST /api/exa-answer with the required field query and pay $0.010 per call over x402 or MPP (there is no free tier). It returns a JSON object with source, fetchedAt, query, answer, citationCount and 1 more.

Exa searches its index, reads the pages and composes the answer, returning the citation list (title, URL, published date) alongside it so every claim can be checked. Model-backed: the answer text is generated, the citations are retrieved.

Category: Web & documents · Tags: web search exa answer citations

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Parameters

Example request

curl -i -X POST https://agent402.tools/api/exa-answer \
  -H "Content-Type: application/json" \
  -d '{"query":"What is the x402 payment protocol and who uses it?"}'

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

Example response

{
  "source": "exa",
  "fetchedAt": "2026-09-13T20:00:00.000Z",
  "query": "What is the x402 payment protocol and who uses it?",
  "answer": "x402 is an HTTP-native payment protocol that settles stablecoin payments per request ...",
  "citationCount": 1,
  "citations": [
    {
      "title": "What is the x402 payment protocol?",
      "url": "https://example.com/x402-explained",
      "publishedDate": "2026-08-02T00:00:00.000Z",
      "author": null,
      "text": null
    }
  ]
}

From an MCP client

catalog.call {
  "slug": "exa-answer",
  "params": {
    "query": "What is the x402 payment protocol and who uses it?"
  }
}

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

Errors and behavior

• query 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 GET or HEAD to /api/exa-answer returns the same 402 quote, so the price can be read without a body.
• 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/exa-answer", {
  method: "POST",
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "query": "What is the x402 payment protocol and who uses it?"
  }),
});

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