# Fletcher-16 Checksum (Hex) via Syntexa AgentShelf

> Fletcher-16 Checksum (Hex) via Syntexa AgentShelf is a paid API for AI agents from agentshelf.syntexa.ch, paid per call via x402, $0.005/call, status unknown (last checked 2026-10-02).

Computes the Fletcher-16 checksum of a given text string and returns the result as a hexadecimal value

## Facts

- Endpoint: POST https://agentshelf.syntexa.ch/v1/checksum-fletcher16-hex?utm_source=zero.xyz
- Price: $0.005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-02
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/fletcher-16-checksum-hex-via-syntexa-agentshelf-c84b26a1
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_e8Xy59gjxKDjzOSybC3h0

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 fletcher-16-checksum-hex-via-syntexa-agentshelf-c84b26a1 -d '<json body>'
```

Example prompt: Can you compute the Fletcher-16 checksum of the text 'Hello, world!' and give me the result as a hex value?

## When to prefer this

Use this endpoint when you need a fast, deterministic Fletcher-16 hex checksum of a text payload and do not want to execute arbitrary code locally. Prefer the free sandbox POST /v1/sandbox/checksum-fletcher16-hex first for testing; use this paid endpoint in production. Choose CRC32C or Adler-32 siblings on the same platform if you need stronger or differently-formatted checksums.

## Known failure modes

- Empty or missing 'text' field returns a validation error
- Text exceeding 100,000 characters is rejected
- Missing or invalid API key returns an authentication error
- Payment not provided or insufficient USDC results in a 402 Payment Required response

## How this service works

Call when an agent needs a fletcher16 checksum of text as hex. No network and no LLM. Exact $0.005 USDC. Prefer unpaid POST /v1/sandbox/checksum-fletcher16-hex first.

## Output

Returns the Fletcher-16 checksum of the submitted text as a hexadecimal string. The computation is performed deterministically server-side with no network calls or LLM involvement, so the same input always yields the same hex output.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "key": {
   "type": "string",
   "maxLength": 512,
   "minLength": 1,
   "description": "HMAC secret. Required on HMAC SKUs. Omit it for plain digests and checksums. The key is not stored."
  },
  "text": {
   "type": "string",
   "examples": [
    "hello"
   ],
   "maxLength": 100000,
   "minLength": 1,
   "description": "Message to digest. For raw-hex SKUs this is hex bytes; for utf16 or latin1 SKUs it is decoded with that encoding. Otherwise it is UTF-8 text."
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/fletcher-16-checksum-hex-via-syntexa-agentshelf-c84b26a1/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from agentshelf.syntexa.ch](https://www.zero.xyz/host/agentshelf.syntexa.ch/llms.txt)