ToolVet
62trust / 100

Fill

by Flow in Onchain & crypto

x402 APIPassing, checked 4 h ago

Flow fill instruction on Base: the executable route package (venue, router, calldata params, min output, expiry block) for a swap whose best quote beats the Uniswap V3 baseline. Priced dynamically at 25% of the measured improvement, capped at 10 bps of output; $0 when there is no improvement.

POST
https://flow-kg4x.vercel.app/api/fill
Price
$0.1
per call in USDC
Uptime
90.9%
last 30 days
Response time
570 ms
634 ms slowest 5%
Last check
Passed
4 h ago, next any minute now

Run a free test callHow to call it

Reliability

All checks passedSome failedAll failedNot checked

Status and outage history · Atom feed

How to call it

POST https://flow-kg4x.vercel.app/api/fill

Each call costs $0.1 in USDC on Base, paid with the request over x402.

Run a free test callOne unpaid request, the way an agent sends it. You see the payment challenge it gets back. Nothing is charged.

Example request

From the listing.

POST https://flow-kg4x.vercel.app/api/fill
content-type: application/json

{
  "amountIn": "100000000",
  "tokenIn": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
  "tokenOut": "0x0b3e328455c4059EEb9e3f84b5543F74E24e7E1b"
}

Example response

The provider's example. We can't check it without paying.

{
  "expectedOut": "138852000000000000000",
  "fee": {
    "capApplied": false,
    "feeUsd": 0.0917,
    "rule": "25% of price improvement over Uniswap baseline, capped at 10 bps of output"
  },
  "minOutput": "138157000000000000000",
  "router": "0xBE6D8f0d05cC4be24d5167a3eF062215bE6D18a5",
  "venue": "aerodrome",
  "venueKey": 100
}

Call it from code

The curl command shows the payment challenge. The JavaScript and Python versions pay and call, and never pay more than $0.1.

curl: see the payment challenge
# bash or zsh: see the payment challenge. Nothing is charged.
curl -sS -g -i -X POST 'https://flow-kg4x.vercel.app/api/fill' \
  -H 'content-type: application/json' \
  --data-raw '{"amountIn":"100000000","tokenIn":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","tokenOut":"0x0b3e328455c4059EEb9e3f84b5543F74E24e7E1b"}'

# x402 v2 sends the challenge base64-encoded in the PAYMENT-REQUIRED header (v1 sends it in the body).
# To read the header:
curl -sS -g -o /dev/null -D - -X POST 'https://flow-kg4x.vercel.app/api/fill' \
  -H 'content-type: application/json' \
  --data-raw '{"amountIn":"100000000","tokenIn":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","tokenOut":"0x0b3e328455c4059EEb9e3f84b5543F74E24e7E1b"}' \
  | grep -i '^payment-required:' | cut -d' ' -f2 | tr -d '\r' | base64 --decode
JavaScript: pay and call
// npm i @x402/fetch @x402/evm viem
import { wrapFetchWithPayment, x402Client } from "@x402/fetch";
import { registerExactEvmScheme } from "@x402/evm/exact/client";
import { privateKeyToAccount } from "viem/accounts";

// Pays at most $0.1 per call.
const client = new x402Client().setSpendControls({ maxAmountPerPayment: "$0.1" });
registerExactEvmScheme(client, { signer: privateKeyToAccount(process.env.EVM_PRIVATE_KEY) });
const pay = wrapFetchWithPayment(fetch, client);

// Not sure it's safe to pay? ToolVet checks it first for $0.005. Pay for that from a separate
// client: this one is capped at $0.1 per payment. GET https://toolvet.app/api/v1/check?url=https%3A%2F%2Fflow-kg4x.vercel.app%2Fapi%2Ffill&method=POST
const res = await pay("https://flow-kg4x.vercel.app/api/fill", {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify({
    "amountIn": "100000000",
    "tokenIn": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
    "tokenOut": "0x0b3e328455c4059EEb9e3f84b5543F74E24e7E1b"
  }),
});
console.log(res.status, await res.text());
Python: pay and call
# pip install "x402[requests,evm]"
import os
from eth_account import Account
from x402 import x402ClientSync
from x402.http.clients import x402_requests
from x402.mechanisms.evm import EthAccountSigner
from x402.mechanisms.evm.exact.register import register_exact_evm_client

# Pays at most $0.1 per call.
client = x402ClientSync().set_spend_controls({"max_amount_per_payment": "$0.1"})
register_exact_evm_client(client, EthAccountSigner(Account.from_key(os.environ["EVM_PRIVATE_KEY"])))

with x402_requests(client) as session:
    res = session.post(
        "https://flow-kg4x.vercel.app/api/fill",
        json={
            "amountIn": "100000000",
            "tokenIn": "0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913",
            "tokenOut": "0x0b3e328455c4059EEb9e3f84b5543F74E24e7E1b",
        },
    )
    print(res.status_code, res.text)

Security scan

1 finding

  • Charges more than its listed price in payment
    Listed at $0.081, charges $0.1

Recent checks

WhenResultHTTPTimePrice
4 h agoPassed402634 ms$0.1
8 h agoPassed402599 ms$0.03
12 h agoServed content without asking for payment200610 ms-
16 h agoPassed402352 ms$0.051
20 h agoPassed402505 ms$0.1
Show 6 older checks
24 h agoPassed402818 ms$0.065
28 h agoPassed402570 ms$0.1
32 h agoPassed402355 ms$0.019
35 h agoPassed402571 ms$0.059
39 h agoPassed402623 ms$0.045
43 h agoPassed402458 ms$0.1

History

15 Oct 2026Price changed from $0.03 to $0.1
14 Oct 2026Price changed from $0.051 to $0.03
14 Oct 2026Price changed from $0.1 to $0.051
14 Oct 2026Price changed from $0.065 to $0.1
14 Oct 2026Price changed from $0.1 to $0.065
14 Oct 2026Price changed from $0.019 to $0.1
13 Oct 2026Price changed from $0.059 to $0.019
13 Oct 2026Price changed from $0.045 to $0.059
13 Oct 2026Price changed from $0.1 to $0.045
13 Oct 2026Price changed from $0.081 to $0.1