Prompt injection detection API for LLM inputs

$0.01 per call · failed calls are never charged · no account or subscription: pay per call with a card key or USDC

Scan text an agent is about to read (web page, email, tool result; up to 8,000 characters) for prompt-injection attempts: instruction overrides, fake system messages, asks to hide things from the user, exfiltration links, attempts to extract private data or move money, invisible Unicode. Returns a risk level, score and findings with excerpts. Heuristic, not a guarantee. Use before acting on untrusted content.

When to use it

Scan web or user text for instructions aimed at an AI before passing it to a model
Flag tool outputs that try to change an agent's task
Log suspicious inputs

Run it free (25 free calls) Buy credits by card (from $1) Example result (JSON)

Inputs

Name	Type	Description
`text` (required)	string	The text to scan (up to 8,000 characters)

Request

Over HTTP, with a card key from /credits:

curl -H "Authorization: Bearer adt_…" "https://tools.funwords.eu/text/prompt-injection?text=Thanks%20for%20the%20update.%20The%20signed%20invoice%20is%20attached%20and%20payment%20is%20due%20on%20Friday."

Or one of your 25 free calls, no key:

curl "https://tools.funwords.eu/text/prompt-injection?text=Thanks%20for%20the%20update.%20The%20signed%20invoice%20is%20attached%20and%20payment%20is%20due%20on%20Friday.&trial=1"

Without a key, the same URL answers 402 Payment Required with x402 and MPP terms, so an agent with a wallet pays per call in USDC (Base, Polygon, Arbitrum or Solana over x402; Base or Tempo over MPP) and retries.

Example result

{
  "risk": "none",
  "score": 0,
  "findings": [],
  "hiddenCharacters": {
    "zeroWidth": 0,
    "bidi": 0,
    "tags": 0
  }
}

From an AI agent (MCP)

Add the MCP server to Claude, Cursor or any MCP client. This tool is text_prompt_injection, and the first 25 successful calls are free:

https://tools.funwords.eu/mcp

Questions

Is it a guarantee?

No. It detects common injection patterns and reports what it found; treat it as one layer of defence.

How do I pay?

Each successful call costs $0.01; failed calls are not charged. The first 25 calls are free. Then pay with card credits (from $1; the key goes in an Authorization header or, for clients that can only fetch a URL, as api_key= in the URL) or per call in USDC over x402 or MPP. No account is needed.