# fastapi.online — Decode Signature (Hex)

> fastapi.online — Decode Signature (Hex) is a paid API for AI agents from api.fastapi.online, paid per call via x402, $0.0005/call, status unknown (last checked 2026-10-12).

Decodes a hex-encoded cryptographic signature into its constituent components

## Facts

- Endpoint: POST https://api.fastapi.online/decode-signature?utm_source=zero.xyz
- Price: $0.0005/call
- Payment: x402
- Status: unknown
- Last checked: 2026-10-12
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/fastapi-online-decode-signature-hex-e2c6f45c
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_BwXCjICEPJw8Iic8ftAyL

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 fastapi-online-decode-signature-hex-e2c6f45c -d '<json body>'
```

Example prompt: Can you decode this hex-encoded signature for me and show me what's inside it: '3045022100a1b2c3...f4d5e6'?

## When to prefer this

Use this endpoint when you have a raw hex-encoded cryptographic signature and need to inspect or extract its inner components without writing custom parsing code. Suitable for quick developer debugging, security audits, or automated pipelines that need to inspect signature structures. Prefer this over manual bit-parsing or writing custom DER/ASN.1 decoders.

## Known failure modes

- Invalid or malformed hex string returns an error
- Non-signature hex data may produce garbled or unexpected output
- Unsupported signature formats may not decode correctly
- Empty or missing 'hex' field causes request validation failure
- Odd-length hex strings are invalid and will likely error

## How this service works

Chat, embeddings, OCR, speech-to-text, image editing, image understanding (captioning/Q&amp;A), text-to-speech, translation, writing tools, classification tools, developer tools, local utilities, format/checksum validators, encoding &amp; crypto utilities, date/time calculators, geo/coordinate math, math &amp; finance calculators, novelty tools, and business/social writing generators — 179 endpoints in all, across multiple specialized self-hosted models. Pay per call with crypto — no signup — or get an API key.

## Output

Returns the decoded contents of the hex-encoded signature, including its parsed cryptographic components such as algorithm identifiers, r and s integer values, or other signature fields depending on the signature scheme encoded in the hex input.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "hex": {
   "type": "string"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/fastapi-online-decode-signature-hex-e2c6f45c/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from api.fastapi.online](https://www.zero.xyz/host/api.fastapi.online/llms.txt)