# Bitcoin HASH256 (Double SHA-256)

> Bitcoin HASH256 (Double SHA-256) is a paid API for AI agents from twin.unykorn.org, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-01).

Computes Bitcoin's HASH256 function — SHA-256 applied twice — on a hex-encoded byte string or plain text input

## Facts

- Endpoint: POST https://twin.unykorn.org/hash-double-sha256?utm_source=zero.xyz
- Price: $0.001/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-01
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/bitcoin-hash256-double-sha-256-3e772154
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_HfCpAK9SykJDxdWq9dIw0

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 bitcoin-hash256-double-sha-256-3e772154 -d '<json body>'
```

Example prompt: Can you compute the Bitcoin HASH256 (double SHA-256) of this hex string: 0x48656c6c6f20576f726c64?

## When to prefer this

Choose this endpoint when you need Bitcoin-standard double SHA-256 hashing (HASH256) as used in Bitcoin transaction ID computation, block hashing, and script opcodes. Prefer it over generic SHA-256 services when you specifically need the Bitcoin double-hash primitive, and when you want a paid, auditable receipt of the computation via the x402 micropayment protocol.

## Known failure modes

- Invalid hex string (not matching ^0x[0-9a-fA-F]* pattern) returns an error response
- Text input exceeding 49152 characters is rejected
- Missing both hex and text parameters results in a bad request error
- Payment failure via x402 protocol prevents execution
- Network timeout on the UnyKorn endpoint

## How this service works

Bitcoin HASH256 — SHA-256 applied twice — Genesis402 / UnyKorn Operator Network

## Output

Returns a JSON object with ok:true, the type field set to 'hash-double-sha256', the resulting digest (SHA-256 applied twice to the input), a timestamp, and a payment receipt including transaction hash, amount in USD, and a receipt ID.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "params": {
   "type": "object",
   "properties": {
    "hex": {
     "type": "string",
     "pattern": "^0x[0-9a-fA-F]*$"
    },
    "text": {
     "type": "string",
     "maxLength": 49152
    }
   }
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "ok": true,
  "type": "hash-double-sha256",
  "receipt": {
   "tx_hash": "0x<64hex>",
   "amount_usd": 0.001,
   "receipt_id": "g402-<16hex>"
  },
  "generated_at": "<iso8601>"
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/bitcoin-hash256-double-sha-256-3e772154/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from twin.unykorn.org](https://www.zero.xyz/host/twin.unykorn.org/llms.txt)