How much does a feed-discover call cost?

$0.002 per call, paid in USDC on Base via x402, with no account and no API key.

What does feed-discover return?

A JSON object with 8 top-level fields: url, source_url, final_url, http_status, feeds, feeds_total, feeds_truncated and fetched_at. The example on this page is a real call over web/fieldnotes/index.html, web/fieldnotes/feed.xml and web/fieldnotes/atom.xml.

What happens when a feed-discover call fails?

The tool answers with a typed JSON error from the errors table. Payment is settled only after the tool has produced its result; a call that fails inside the tool is never settled. A 503 upstream_unavailable can follow a settled call; the x402 payments guide covers it, 429, 402 and an uncertain 500.

catalogue / tools / Feeds & site structure / Feed Discover API

Feed Discover API

Fetches a web page and returns the RSS, Atom and JSON feeds it declares in its <head>, as absolute URLs with their type and title.

Endpoint: POST /v1/feed-discover
Price: $0.002 per call
Family: Feeds & site structure
Docs: /docs/feed-discover

01When to use it

It needs the network, and the feed an agent wants is declared in the page it already has as a <link rel="alternate"> -- one guarded fetch and a DOM query returns it, where feeding the whole page to a model costs far more in tokens and still guesses.

When not to use it

The input is over 5 MB (5,242,880 bytes): feed-discover answers too_large (413).
The destination needs more than 8 s to answer: the call ends with upstream_timeout (424).
The destination is on a private or local network: the network guard refuses it with blocked_target (403).

02Parameters

Field	Type	Required	Description
url	string	yes	Absolute http(s) URL of the HTML or XHTML page whose <link rel="alternate"> or rel="feed" declarations with an RSS, Atom or JSON Feed media type are read, up to 2048 characters; up to 5 redirects are followed and no feed paths are probed.

03Limits

Limit	Value
Size cap	5 MB (5,242,880 bytes)
Timeout	8 s

04Example

The published example of feed-discover, verbatim: the request body and the response it returns.

Request

POST /v1/feed-discover
content-type: application/json
payment-signature: <base64 x402 payload>

{
  "url": "https://grist.tools/samples/web/fieldnotes/index.html"
}

Response

200 OK
payment-response: <base64 settlement receipt>

{
  "url": "https://grist.tools/samples/web/fieldnotes/index.html",
  "source_url": "https://grist.tools/samples/web/fieldnotes/index.html",
  "final_url": "https://grist.tools/samples/web/fieldnotes/index.html",
  "http_status": 200,
  "feeds": [
    {
      "url": "https://grist.tools/samples/web/fieldnotes/feed.xml",
      "type": "rss",
      "title": "Field Notes (RSS)",
      "rel": "alternate"
    },
    {
      "url": "https://grist.tools/samples/web/fieldnotes/atom.xml",
      "type": "atom",
      "title": "Field Notes (Atom)",
      "rel": "alternate"
    }
  ],
  "feeds_total": 2,
  "feeds_truncated": false,
  "fetched_at": "2026-09-01T12:00:00.000Z"
}

Sample file: web/fieldnotes/index.html. Sample file: web/fieldnotes/feed.xml. Sample file: web/fieldnotes/atom.xml. Atom 1.0 feed of the Field Notes sample site, carrying the same two notes as feed.xml.

Response field	Type	In the example
url	string	"https://grist.tools/samples/web/fieldnotes/index.html"
source_url	string	"https://grist.tools/samples/web/fieldnotes/index.html"
final_url	string	"https://grist.tools/samples/web/fieldnotes/index.html"
http_status	number	200
feeds	array	2 items, each with url, type, title and rel
feeds_total	number	2
feeds_truncated	boolean	false
fetched_at	string	"2026-09-01T12:00:00.000Z"

05Call it from code

JavaScript

// feed-discover: $0.002 per call, paid in USD Coin on eip155:8453 via x402
// Install: npm install @x402/fetch@2 @x402/evm@2 viem@2
// Save as client.mjs (ES module, Node 18+), export EVM_PRIVATE_KEY with the paying wallet's key in your shell, then run: node client.mjs
// The wrapper reads the 402 (payment-required), signs and retries with payment-signature.
import { wrapFetchWithPayment, x402Client, decodePaymentResponseHeader } from '@x402/fetch'
import { ExactEvmScheme } from '@x402/evm/exact/client'
import { privateKeyToAccount } from 'viem/accounts'

const account = privateKeyToAccount(process.env.EVM_PRIVATE_KEY)
const client = new x402Client().register('eip155:8453', new ExactEvmScheme(account))
const fetchWithPayment = wrapFetchWithPayment(fetch, client)

const body = {
  "url": "https://grist.tools/samples/web/fieldnotes/index.html"
}

const res = await fetchWithPayment('https://grist.tools/v1/feed-discover', {
  method: 'POST',
  headers: { 'content-type': 'application/json' },
  body: JSON.stringify(body),
})
console.log(res.status, await res.json())
const settle = res.headers.get('payment-response')
if (settle) console.log(decodePaymentResponseHeader(settle).transaction)

Python

# feed-discover: $0.002 per call, paid in USD Coin on eip155:8453 via x402
# Install: pip install "x402[requests,evm]>=2.24,<3"
# The session reads the 402 (payment-required), signs and retries with payment-signature.
import os
from eth_account import Account
from x402 import x402ClientSync
from x402.http import decode_payment_response_header
from x402.http.clients.requests import x402_requests
from x402.mechanisms.evm.exact import register_exact_evm_client
from x402.mechanisms.evm.signers import EthAccountSigner

account = Account.from_key(os.environ["EVM_PRIVATE_KEY"])
client = x402ClientSync()
register_exact_evm_client(client, EthAccountSigner(account), networks="eip155:8453")
session = x402_requests(client)

payload = {
    "url": "https://grist.tools/samples/web/fieldnotes/index.html"
}

res = session.post("https://grist.tools/v1/feed-discover", json=payload)
print(res.status_code, res.json())
settle = res.headers.get("payment-response")
if settle:
    print(decode_payment_response_header(settle).transaction)

curl

# feed-discover: $0.002 per call, paid in USD Coin on eip155:8453 via x402
# 1. Unpaid call: HTTP 402, the requirements in the payment-required header (base64 JSON) and in the body.
curl -i -X POST 'https://grist.tools/v1/feed-discover' -H 'content-type: application/json' -d '{"url":"https://grist.tools/samples/web/fieldnotes/index.html"}'

# 2. Same call with the signed payment (an EIP-3009 authorization, EIP-712 signed: it cannot be
#    typed by hand). x-payment is accepted as the v1 alternative. HTTP 200 carries payment-response.
curl -i -X POST 'https://grist.tools/v1/feed-discover' -H 'content-type: application/json' -H 'payment-signature: <base64 x402 payload>' -d '{"url":"https://grist.tools/samples/web/fieldnotes/index.html"}'

06Errors

Code	HTTP	For this service
invalid_input	400	The body does not match the schema; its fields are url.
blocked_target	403
unreachable_target	424
upstream_status	424
upstream_timeout	424
unsupported_content_type	415
too_large	413
internal	500

Input that is rejected before the tool runs (malformed JSON, schema mismatch, body over the size limit) is never charged.

When each code is raised, and what it means for payment: /docs/feed-discover.

07Questions

How much does a feed-discover call cost?: $0.002 per call, paid in USDC on Base via x402, with no account and no API key.
What does feed-discover return?: A JSON object with 8 top-level fields: url, source_url, final_url, http_status, feeds, feeds_total, feeds_truncated and fetched_at. The example on this page is a real call over web/fieldnotes/index.html, web/fieldnotes/feed.xml and web/fieldnotes/atom.xml.
What happens when a feed-discover call fails?: The tool answers with a typed JSON error from the errors table. Payment is settled only after the tool has produced its result; a call that fails inside the tool is never settled. A 503 upstream_unavailable can follow a settled call; the x402 payments guide covers it, 429, 402 and an uncertain 500.