# Crypto Fear & Greed Index API

> Crypto Fear & Greed Index API is a paid API for AI agents from fear-greed.hergertsynthora.com, paid per call via x402, $0.05/call, status unknown (last checked 2026-09-14).

Returns the real-time crypto Fear & Greed index (0–100) with sentiment classification and historical data points

## Facts

- Endpoint: POST https://fear-greed.hergertsynthora.com/service
- Price: $0.05/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-14
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/crypto-fear-greed-index-api-b12b627c
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_kEO0NH_-1Tpu0a7RZcK1w

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 crypto-fear-greed-index-api-b12b627c -d '<json body>'
```

Example prompt: What's the current crypto Fear & Greed index right now, and can you also give me the last 10 historical readings?

## When to prefer this

Use this endpoint when an agent needs a real-time or recent-historical crypto market sentiment signal — particularly for portfolio allocation decisions, rebalancing triggers, or risk-on/risk-off logic. Prefer this over general news sentiment APIs when you need a single authoritative 0–100 index number with classification rather than raw text analysis.

## Known failure modes

- Upstream data source failure — no charge applied per service terms
- Invalid limit parameter type returns schema validation error
- Missing or malformed X-WALLET header may affect free-tier tracking
- Network timeout if upstream provider is slow

## How this service works

Real-time crypto Fear & Greed index (0-100) with classification and history. Market-sentiment signal for allocation agents. Free source, deterministic. $0.005 USDC via x402 on Base. SYNTHORA. First 3 calls FREE per wallet — send header X-WALLET: 0x<addr>. No charge on upstream failure.

## Output

Returns a numeric Fear & Greed index value between 0 and 100, a human-readable sentiment classification (e.g. Extreme Fear, Fear, Neutral, Greed, Extreme Greed), and optionally a list of historical index data points up to the requested limit.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "properties": {
  "input": {
   "type": "string",
   "description": "SYNTHORA fear-greed: indice de miedo/codicia con la VARIACION frente a ayer y el cruce de banda, no solo el valor. Fuente: alternative.me, fechada y con hash."
  }
 }
}
```

## Response schema (JSON Schema)

```json
{
 "type": "json",
 "example": {
  "ok": true,
  "niche": "fear_greed",
  "result": {
   "senal": "el indice cambia de 'Extreme Fear' a 'Fear': giro de regimen de sentimiento",
   "value": 27,
   "fuente": "<omitido en el ejemplo publico>",
   "serie_8d": [
    27,
    25,
    "..."
   ],
   "as_of_utc": "2026-08-05T16:31:27Z",
   "maximo_8d": 29,
   "minimo_8d": 25,
   "latencia_s": 0.33,
   "delta_vs_ayer": 2,
   "classification": "Fear",
   "cambio_de_banda": true,
   "clasificacion_ayer": "Extreme Fear"
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/crypto-fear-greed-index-api-b12b627c/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from fear-greed.hergertsynthora.com](https://www.zero.xyz/host/fear-greed.hergertsynthora.com/llms.txt)