> ## 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 Access

> The three channels onto Belief index and Belief Volatility data – the Data API for programs, the MCP server for AI assistants, point-in-time snapshots for the full record – all behind one free account.

Belief index levels, Belief Volatility series, and the point-in-time record reach you through three channels. The data and the terms are the same in all three. What differs is what is doing the reading.

| Channel                                   | Read by                                            | Carries                                                                                                                            | First step                                  |
| ----------------------------------------- | -------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------- |
| **[Data API](/data-access/data-api)**     | Programs, notebooks, dashboards                    | Latest levels, trailing 90-day history at `1h` or `1d`, the volatility catalog and history, reconstitution events                  | [Mint a key](/data-access/data-api)         |
| **[MCP server](/data-access/mcp-server)** | AI assistants and agents                           | The same data as eight tools over the Model Context Protocol                                                                       | [Add a header](/data-access/mcp-server)     |
| **[Snapshots](/data-access/downloads)**   | Analysts and researchers who want the whole record | Full aggregate history since inception, composition membership and target weights, reconstitution arithmetic, as dated CSV bundles | [Download a bundle](/data-access/downloads) |

## One account, one key

A single account at [beliefsystems.xyz/data](https://beliefsystems.xyz/data) issues one credential – a `belief_live_` key – and that key opens all three channels. The API authenticates with it, an MCP client sends it as an `Authorization` header, and snapshot files accept it directly or accept a signed-in browser session instead.

Registration is free and takes about a minute: work email, no password, a magic link. Each account holds up to three active keys, rotates and revokes them from the portal, and sees its own usage there.

## What the channels do not carry

Constituent compositions, the per-market panel, raw NAV, and sub-hourly granularity are not on the API or MCP. [Data boundaries](/data-access/data-api-boundaries) states each line and where the rest lives.

<CardGroup cols={2}>
  <Card title="Data API quickstart" icon="terminal" href="/data-access/data-api">
    Base URL, authentication, and a first call in three steps.
  </Card>

  <Card title="MCP server" icon="plug" href="/data-access/mcp-server">
    Client configuration, the tool reference, and scope.
  </Card>

  <Card title="Snapshot downloads" icon="download" href="/data-access/downloads">
    What each bundle contains, how to fetch it, and how to cite it.
  </Card>

  <Card title="Limits and errors" icon="gauge" href="/data-access/data-api-limits">
    Rate limits, headers, error codes, and the history window.
  </Card>

  <Card title="Data boundaries" icon="signs-post" href="/data-access/data-api-boundaries">
    What each lane carries, and how `/v1` changes over time.
  </Card>

  <Card title="Index Services" icon="file-contract" href="https://beliefsystems.xyz/license">
    Production rights, redistribution, and full-fidelity data.
  </Card>
</CardGroup>