# Keccak-256 Hash via FastX402

> Keccak-256 Hash via FastX402 is a paid API for AI agents from fastx402.tools, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-17).

Computes the Keccak-256 (Ethereum-native SHA-3) hash of a UTF-8 string or hex-encoded bytes, returning the hex digest and input byte count.

## Facts

- Endpoint: GET https://fastx402.tools/keccak256?utm_source=zero.xyz
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-17
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/keccak-256-hash-via-fastx402-abadff99
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_Dyzs3df5gJagrgBHFxRNi

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability keccak-256-hash-via-fastx402-abadff99
```

Example prompt: What's the Keccak-256 hash of the text 'Transfer(address,address,uint256)'? I need it to get the Ethereum event topic hash.

## When to prefer this

Choose this endpoint when you need the Keccak-256 (Ethereum-native) variant of SHA-3 specifically — not standard SHA-3/FIPS-202, which uses different padding. Ideal for Ethereum development tasks such as computing event topic hashes, function selectors, address derivation checks, or any on-chain data verification. No API key or account required; payment is per-call via USDC on Base.

## Known failure modes

- Missing both 'hex' and 'text' query params — server returns an error indicating input is required
- Malformed hex string (odd length or non-hex characters) — parsing error returned
- Payment not provided or insufficient — 402 Payment Required response before computation occurs
- Empty 0x input treated as empty bytes, returning the Keccak-256 of zero bytes

## How this service works

146 pay-per-call tools for AI agents, from $0.001 per request in USDC on Base or Solana with x402. No account, no API key.

## Output

A JSON object containing 'hash' (the 0x-prefixed 64-character Keccak-256 hex digest) and 'input_bytes' (the number of bytes consumed from the input), e.g. {"hash":"0x1c8aff...","input_bytes":5}.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method"
   ],
   "properties": {
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "GET"
     ],
     "type": "string"
    },
    "queryParams": {
     "type": "object",
     "required": [],
     "properties": {
      "hex": {
       "type": "string",
       "description": "Hex bytes to hash, like 0x68656c6c6f; \"0x\" is empty"
      },
      "text": {
       "type": "string",
       "description": "UTF-8 text to hash"
      }
     }
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object",
     "properties": {
      "hash": {
       "type": "string"
      },
      "input_bytes": {
       "type": "integer"
      }
     }
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "hash": "0x1c8aff950685c2ed4bc3174f3472287b56d9517b9c948127319a09a7a36deac8",
  "input_bytes": 5
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/keccak-256-hash-via-fastx402-abadff99/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from fastx402.tools](https://www.zero.xyz/host/fastx402.tools/llms.txt)