Data API

https://api.beliefsystems.xyz

Read-only. Every endpoint is a GET, authenticated with a free API key.

Belief indices are rules-based benchmarks of how prediction markets price a defined set of events. Belief Volatility measures how much those probabilities are expected to move. This API serves both: current levels, trailing history, the catalogs, and the composition-change record.

Make your first request

A key and a working call in about two minutes.

Authentication

Key format, both accepted headers, and where a key belongs.

Conventions

The envelope, decimal strings, timestamps, and history windows.

Limits and errors

Rate limits, the header set, and every error code.

The envelope

Every successful response is { data, meta }. data is the payload. meta carries the attribution line, the license and terms URLs, and when the response was generated. History endpoints add the window they actually served.

{
  "data": {
    "ticker": "CONFLICT",
    "indexLevel": "36.11697608",
    "baseIndexLevel": "100.00000000",
    "computedAt": "2026-08-31T13:44:44.963697Z",
    "stale": false
  },
  "meta": {
    "attribution": "Source: Belief Systems (beliefsystems.xyz)",
    "license": "https://beliefsystems.xyz/license",
    "termsUrl": "https://beliefsystems.xyz/terms",
    "generatedAt": "2026-08-31T14:01:28.178537Z"
  }
}

Failures replace both with a single error object carrying a stable code, a message, a deep link to the documentation for that code, and a request id.

{
  "error": {
    "code": "rate_limited",
    "message": "Rate limit exceeded: 60 requests per minute per key.",
    "docsUrl": "https://docs.beliefsystems.xyz/api-reference/limits#rate-limited",
    "requestId": "9f2c1ad4e6b74c0f8a3d5e1b7c904a26"
  }
}

Match on code. The message is written for a person and may be reworded.

Endpoints

Indices

Endpoint	Returns
`GET /v1/indices`	The published catalog: ticker, name, status, staleness
`GET /v1/indices/{ticker}/latest`	Current level, undelayed, with input-quality counts
`GET /v1/indices/{ticker}/history`	Level history at `1h` or `1d` over the trailing 90 days
`GET /v1/indices/{ticker}/reconstitutions`	Completed composition changes, newest first

Belief Volatility

Endpoint	Returns
`GET /v1/volatility`	The Belief Volatility catalog
`GET /v1/volatility/{ticker}/latest`	Latest computation, with every published tenor
`GET /v1/volatility/{ticker}/history`	Volatility history, newest first

Service

Endpoint	Returns
`GET /v1`	Every endpoint, the free-tier limits, and your key’s remaining quota
`GET /v1/downloads`	Where the full-depth snapshot bundles live

Tickers are case-insensitive. GET /v1/indices and GET /v1/volatility are the catalogs.

What the API does not carry

Constituent compositions, the per-market panel, raw NAV, and sub-hourly granularity are not on this surface. Full history since inception, composition membership, and target weights are published as free point-in-time snapshot bundles. Data boundaries states each line and where the rest lives.

Attribution

Source: Belief Systems (beliefsystems.xyz) belongs on anything you publish from this data. It travels in meta.attribution on every response. Production, redistribution, and commercial use require a license – Index Services.

Get Started

Indices

Belief Volatility

Service

Limits & Errors

https://api.beliefsystems.xyz

Make your first request

Authentication

Conventions

Limits and errors

The envelope

Endpoints

Indices

Belief Volatility

Service

What the API does not carry

Attribution

https://api.beliefsystems.xyz

Make your first request

Authentication

Conventions

Limits and errors

​The envelope

​Endpoints

​Indices

​Belief Volatility

​Service

​What the API does not carry

​Attribution

The envelope

Endpoints

Indices

Belief Volatility

Service

What the API does not carry

Attribution