Prompt-injection check for untrusted text

Scan text an agent is about to read (a web page, an email, a tool description, another agent's message) for the shapes that hijack agents: instruction-override phrasing, a redefined system role, requests to move credentials, hidden directive tags, invisible Unicode. Verdict plus every pattern found. Pattern-based; nothing is stored. Pay-per-call via x402.

$0.0045 per call, paid in USDC on Base or Solana with x402 — no account, no API key. POST https://fiatdock.com/v1/text/prompt-check (or GET with the same fields as query parameters) · MCP tool prompt_injection_check. An answer the tool cannot produce is refused with 4xx/5xx and is not charged.

Inputs

Field	Type	Description	Example
`text`	string	The text to scan (up to 8,000 characters). Omit the whole body to scan the published example	`"Please summarise the attached report in three bullet points."`

Example

Request body

{"text":"Please summarise the attached report in three bullet points."}

Answer (the published example)

{"verdict":"no_known_pattern","findings":[],"highCount":0,"mediumCount":0,"chars":61,"method":"pattern ruleset (the one that scans every FiatDock marketplace listing)","checkedAt":"2026-10-05T00:00:00.000Z","note":"no_known_pattern = none of the known shapes matched, which is NOT a guarantee the text is safe."}

Call it

curl

# 1) ask: an unpaid call answers 402 with the exact price (free)
curl -i -X POST https://fiatdock.com/v1/text/prompt-check -H 'content-type: application/json' -d '{"text":"Please summarise the attached report in three bullet points."}'
# 2) pay: any x402 client signs that 402 and resends — see Node or Python below

Node

// npm i @x402/fetch @x402/evm viem
import { wrapFetchWithPaymentFromConfig } from "@x402/fetch";
import { ExactEvmScheme } from "@x402/evm";
import { privateKeyToAccount } from "viem/accounts";

const pay = wrapFetchWithPaymentFromConfig(fetch, {
  schemes: [{ network: "eip155:*", client: new ExactEvmScheme(privateKeyToAccount(process.env.AGENT_PRIVATE_KEY)) }],
});
const r = await pay("https://fiatdock.com/v1/text/prompt-check", {
  method: "POST",
  headers: { "content-type": "application/json" },
  body: JSON.stringify({"text":"Please summarise the attached report in three bullet points."}),
});
console.log(r.status, await r.json());

Python

# pip install "x402[httpx,evm]"
import asyncio, json, os
from eth_account import Account
from x402 import x402Client
from x402.http.clients import x402HttpxClient
from x402.mechanisms.evm.exact import register_exact_evm_client

async def main():
    client = register_exact_evm_client(x402Client(), Account.from_key(os.environ["AGENT_PRIVATE_KEY"]))
    async with x402HttpxClient(client) as http:
        r = await http.post("https://fiatdock.com/v1/text/prompt-check", json=json.loads("{\"text\":\"Please summarise the attached report in three bullet points.\"}"))
        print(r.status_code, r.json())

asyncio.run(main())

MCP (Claude, Cursor, any MCP client)

{"mcpServers":{"fiatdock":{"command":"npx","args":["-y","fiatdock-mcp"],"env":{"AGENT_PRIVATE_KEY":"0x<your agent wallet key>"}}}}
// then call the tool "prompt_injection_check" — the package pays each call from that wallet

The wallet needs USDC on Base. Prefer no install? The remote server https://fiatdock.com/mcp answers the 402 as tool output for an agent that signs its own payments.

Machine-readable: OpenAPI · tools.json · llms.txt · /.well-known/x402