> ## Documentation Index
> Fetch the complete documentation index at: https://docs.beliefsystems.xyz/llms.txt
> Use this file to discover all available pages before exploring further.
# Data API
> The keyed REST surface for Belief index levels and Belief Volatility series – base URL, authentication, the response envelope, and a first call in curl, Python, or JavaScript.
**Base URL:** `https://api.beliefsystems.xyz`
**Authentication:** `Authorization: Bearer belief_live_…`
## Quickstart
Create an account and [mint a key](https://beliefsystems.xyz/data/signup?source=docs-quickstart) in the portal. Free, work email, about a minute. The secret is shown once.
```bash curl theme={null}
export BELIEF_API_KEY="belief_live_…"
curl -s https://api.beliefsystems.xyz/v1/indices/CONFLICT/latest \
-H "Authorization: Bearer $BELIEF_API_KEY"
```
```python Python theme={null}
import os
import requests
resp = requests.get(
"https://api.beliefsystems.xyz/v1/indices/CONFLICT/latest",
headers={"Authorization": f"Bearer {os.environ['BELIEF_API_KEY']}"},
timeout=10,
)
resp.raise_for_status()
latest = resp.json()["data"]
print(latest["ticker"], latest["indexLevel"], latest["computedAt"])
```
```javascript JavaScript theme={null}
const res = await fetch("https://api.beliefsystems.xyz/v1/indices/CONFLICT/latest", {
headers: { Authorization: `Bearer ${process.env.BELIEF_API_KEY}` },
});
if (!res.ok) throw new Error(`Belief Systems API ${res.status}`);
const { data } = await res.json();
console.log(data.ticker, data.indexLevel, data.computedAt);
```
`X-API-Key` is accepted for the same secret. `Authorization: Bearer` is the canonical form and the one every example here uses.
Every successful response is `{ data, meta }`. `data` is the payload; `meta` carries the attribution line, the license and terms URLs, and the moment the response was generated. History endpoints add the effective window to `meta`.
```json theme={null}
{
"data": {
"ticker": "CONFLICT",
"name": "Belief Global Conflict Risk Escalation Expectations Index",
"computedAt": "2026-08-29T23:05:31.969917Z",
"indexLevel": "35.47662726",
"baseIndexLevel": "100.00000000",
"stale": false,
"publicStatus": "active",
"maturityType": "PERPETUAL",
"compositionVersion": "24ecfc71d2ddb86c",
"methodologyVersion": "midprice-v1",
"inceptionAt": "2026-04-24T13:38:30.565565Z",
"seriesPartiallyResolved": true,
"seriesFullyResolved": false,
"resolvedAt": null,
"ceasedAt": null,
"dataQuality": {
"freshMarketsCount": 24,
"staleMarketsCount": 0,
"totalMarketsCount": 24,
"freshDataPct": 100.0
}
},
"meta": {
"attribution": "Source: Belief Systems (beliefsystems.xyz)",
"license": "https://beliefsystems.xyz/license",
"termsUrl": "https://beliefsystems.xyz/terms",
"generatedAt": "2026-08-29T23:07:04.118204Z"
}
}
```
Levels are decimal strings, not JSON numbers – `"35.47662726"` rather than `35.47662726`. They are exact as published, so parse them with a decimal type wherever the arithmetic has to round-trip. Timestamps are UTC with microsecond precision. Every index carries `baseIndexLevel` 100 at inception, which is what makes a level readable on its own: in the response above, `CONFLICT` at 35.48 is down 64.5% from its inception base.
`Source: Belief Systems (beliefsystems.xyz)` belongs on anything you publish from this data. It travels in `meta.attribution` on every response.
`/v1` answers cross-origin preflights only for Belief Systems' own origins, so browser JavaScript on your domain will fail. Treat it as server-to-server: call it from your backend, which is also where the key belongs – a key shipped to a browser is a published key. Non-production environments allow `localhost`, so a prototype that works against staging will not work in production.
There is no test mode. The API is read-only, so a live key is safe to use in development.
## Endpoints
| Endpoint | Returns |
| ------------------------------------------ | --------------------------------------------------------------------------------------------------------------- |
| `GET /v1` | Service index: every endpoint, the free-tier limits, and a `key` block with your own limits and remaining quota |
| `GET /v1/indices` | The index catalog – ticker, name, publication status, last computation, staleness |
| `GET /v1/indices/{ticker}/latest` | Latest level, undelayed, with data-quality counts |
| `GET /v1/indices/{ticker}/history` | Level history. `start`, `end`, and `interval` (`1h` or `1d`) are all optional |
| `GET /v1/indices/{ticker}/reconstitutions` | Completed composition changes, newest first |
| `GET /v1/volatility` | The Belief Volatility catalog |
| `GET /v1/volatility/{ticker}/latest` | Latest computed tick and latest published value |
| `GET /v1/volatility/{ticker}/history` | Belief Volatility history, newest first |
| `GET /v1/downloads` | Where the full-depth [snapshot bundles](/data-access/downloads) live |
Each endpoint's parameters, with a try-it panel, are in the API Reference tab. Tickers are case-insensitive; `GET /v1/indices` is the catalog.
The volatility endpoints return the envelope of the published `/volatility` surface verbatim – `series`, `publicationState`, `tick`, `published` inside `data` – rather than the flatter shape the index endpoints use. The website, the MCP tools, and `/v1` all read the same structure, so a Belief Volatility value quoted from one channel always matches the other two. [Belief Volatility methodology](/volatility/methodology) defines each field.
## Next
Rate limits, the header set, error codes, and the 90-day window.
What the API serves, where the rest lives, and how `/v1` changes.
The same data as tools, on the same key.