> ## 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. # Service index > Every endpoint on this version, the free-tier limits, and your key's own limits and remaining quota in one call. Use it as a health check and as the authoritative answer to "how much do I have left". The quota figures in `key` are read, not spent: this call costs one request like any other, and the numbers it reports are the ones remaining after it. Read `key` rather than `limits` whenever the two disagree. `limits` describes the free tier; `key` describes you. ## OpenAPI ````yaml /api-reference/openapi.json get /v1 openapi: 3.1.0 info: contact: name: Belief Systems url: https://beliefsystems.xyz/data description: >- Rules-based benchmark data for prediction markets: Belief index levels and Belief Volatility series, read over HTTPS with an API key. The API is read-only. Every endpoint is a `GET`, every successful response is `{ data, meta }`, and every failure is a single `error` object with a stable `code`. Keys are free and take about a minute to mint at https://beliefsystems.xyz/data. Attribution is required on anything you publish from this data: "Source: Belief Systems (beliefsystems.xyz)". Production, redistribution, and commercial use require a license (https://beliefsystems.xyz/license). license: name: Belief Systems Data License url: https://beliefsystems.xyz/license termsOfService: https://beliefsystems.xyz/terms title: Belief Systems Data API version: '1.0' servers: - description: Production. There is no separate test host; the API is read-only. url: https://api.beliefsystems.xyz security: - bearerAuth: [] - apiKeyAuth: [] tags: - description: >- Belief indices are rules-based benchmarks of how prediction markets price a defined set of events. Levels are exact decimal strings based at 100 on the index's inception date. name: Indices - description: >- Belief Volatility measures how much prediction-market probabilities are expected to move over a stated horizon, in probability points. Always name the tenor when quoting a value. name: Belief Volatility - description: >- The service index, which reports your key's live quota, and pointers to the free point-in-time snapshot bundles. name: Service paths: /v1: get: tags: - Service summary: Service index description: >- Every endpoint on this version, the free-tier limits, and your key's own limits and remaining quota in one call. Use it as a health check and as the authoritative answer to "how much do I have left". The quota figures in `key` are read, not spent: this call costs one request like any other, and the numbers it reports are the ones remaining after it. Read `key` rather than `limits` whenever the two disagree. `limits` describes the free tier; `key` describes you. operationId: getServiceIndex responses: '200': content: application/json: example: data: docsUrl: https://docs.beliefsystems.xyz/api-reference/introduction endpoints: - description: >- Service index: endpoints, limits, and your remaining quota path: /v1 - description: The published index catalog with staleness labels path: /v1/indices - description: Current level, not delayed path: /v1/indices/{ticker}/latest - description: Level history at 1h or 1d path: /v1/indices/{ticker}/history - description: Completed composition changes path: /v1/indices/{ticker}/reconstitutions - description: The Belief Volatility catalog path: /v1/volatility - description: Latest published volatility reading path: /v1/volatility/{ticker}/latest - description: Volatility history path: /v1/volatility/{ticker}/history - description: Pointers to the free point-in-time snapshots path: /v1/downloads key: limitDay: 2000 limitMinute: 60 prefix: belief_live_a1b2c3d4 remainingDay: 1873 remainingMinute: 59 limits: historyMaxDays: 90 intervals: - 1h - 1d requestsPerDay: 2000 requestsPerMinute: 60 version: v1 meta: attribution: 'Source: Belief Systems (beliefsystems.xyz)' generatedAt: '2026-08-31T14:01:22.277647Z' license: https://beliefsystems.xyz/license termsUrl: https://beliefsystems.xyz/terms schema: $ref: '#/components/schemas/ServiceIndexResponse' description: Success. '401': content: application/json: example: error: code: invalid_api_key docsUrl: >- https://docs.beliefsystems.xyz/api-reference/limits#invalid-api-key message: >- This endpoint requires a Data API key. Create one free at https://beliefsystems.xyz/data ; programmatic or commercial licensing is at https://beliefsystems.xyz/license. requestId: 9f2c1ad4e6b74c0f8a3d5e1b7c904a26 schema: $ref: '#/components/schemas/Error' description: Missing or unresolvable API key. '429': content: application/json: example: error: code: rate_limited docsUrl: >- https://docs.beliefsystems.xyz/api-reference/limits#rate-limited message: 'Rate limit exceeded: 60 requests per minute per key.' requestId: 9f2c1ad4e6b74c0f8a3d5e1b7c904a26 schema: $ref: '#/components/schemas/Error' description: >- Rate limited. Sleep for `Retry-After` seconds, which is exact on both windows. default: content: application/json: schema: $ref: '#/components/schemas/Error' description: Error. Every /v1 failure uses this shape. x-codeSamples: - label: curl lang: curl source: |- curl -s "https://api.beliefsystems.xyz/v1" \ -H "Authorization: Bearer $BELIEF_API_KEY" - label: Python lang: python source: |- import os import requests resp = requests.get( "https://api.beliefsystems.xyz/v1", headers={"Authorization": f"Bearer {os.environ['BELIEF_API_KEY']}"}, timeout=10, ) resp.raise_for_status() payload = resp.json() print(payload["data"]) - label: JavaScript lang: javascript source: |- const res = await fetch("https://api.beliefsystems.xyz/v1", { headers: { Authorization: `Bearer ${process.env.BELIEF_API_KEY}` }, }); if (!res.ok) throw new Error(`Belief Systems API ${res.status}`); const { data, meta } = await res.json(); console.log(data); components: schemas: ServiceIndexResponse: properties: data: properties: docsUrl: description: The Data API documentation. format: uri type: string endpoints: description: Every endpoint on this version, with a one-line description. items: properties: description: type: string path: example: /v1/indices/{ticker}/latest type: string type: object type: array key: description: >- Your key's own limits and remaining quota. These are the figures actually in force; the `limits` block above describes the free tier. Read this block when the two disagree. Null for unmetered internal keys. properties: limitDay: description: Requests allowed per day for this key. type: integer limitMinute: description: Requests allowed per minute for this key. type: integer prefix: description: The key's display prefix, for telling several keys apart. example: belief_live_a1b2c3d4 type: string remainingDay: description: >- Requests left in the current day window. Peeked, not consumed. type: integer remainingMinute: description: >- Requests left in the current minute window. Peeked, not consumed. type: integer type: - object - 'null' limits: description: The free-tier limits. Your key's effective limits are in `key`. properties: historyMaxDays: description: How far back history endpoints reach, in days. example: 90 type: integer intervals: description: Accepted values for the `interval` parameter. example: - 1h - 1d items: type: string type: array requestsPerDay: example: 2000 type: integer requestsPerMinute: example: 60 type: integer type: object version: description: The API version this document describes. example: v1 type: string type: object meta: properties: attribution: description: >- The attribution line required on anything you publish from this data. Reproduce it verbatim. example: 'Source: Belief Systems (beliefsystems.xyz)' type: string generatedAt: description: >- When this response was generated. UTC timestamp with microsecond precision, `Z`-suffixed. format: date-time type: string license: description: Terms covering production, redistribution, and commercial use. format: uri type: string termsUrl: description: Terms of Service. format: uri type: string required: - attribution - license - termsUrl - generatedAt type: object required: - data - meta type: object Error: description: >- Every failure replaces `data` and `meta` with a single `error` object. Match on `code`, which is a stable contract. `message` is written for a person and may be reworded. properties: error: properties: code: description: Stable machine-readable error code. enum: - invalid_api_key - ip_rate_limited - rate_limited - daily_limit_reached - not_found - invalid_parameter - invalid_interval - invalid_window - method_not_allowed - internal_error - unavailable - error type: string docsUrl: description: Deep link to this code on the limits and errors page. format: uri type: string message: description: Human-readable explanation. Not a stable contract. type: string requestId: description: >- Correlation id, also returned as the X-Request-Id header. Quote it in support requests. type: string required: - code - message - docsUrl - requestId type: object required: - error title: Error type: object securitySchemes: bearerAuth: description: >- Your Data API key as a Bearer token: `Authorization: Bearer belief_live_...`. This is the canonical form. Keys belong on a server, never in a browser. scheme: bearer type: http apiKeyAuth: description: >- The same key sent as `X-API-Key` instead. Accepted everywhere the Bearer header is. Send one or the other, not both. in: header name: X-API-Key type: apiKey ````