Helious Reference API

openapi: 3.2.0
info:
  title: Helious Public Reference API
  version: '2026-11-06'
  summary: Real-time US economic releases, Treasury auction results, rates and market news from the Helious desk.
  description: 'Read-only surface of api.helious.io. Every dataset here is first-party: captured by the Helious desk the moment it prints, with methodology at https://helious.io/methodology. On /v1/feed and the stream the Helious news wire rides beside the desk''s own posts: a wire headline is marked kind: headline and scored like everything else. The /v1 endpoints are the versioned contract for agents, and every tier sees the same endpoints and the same response shapes: only the history window, the delay and the market-data axis change, so an integration built keyless survives every upgrade untouched. The ladder: Sample (no key, no account, $0) gets 1 day of history, news and prints 1 hour behind, no market prices at all (price endpoints answer with the upgrade steps instead of numbers) and 30 calls a minute and 50 credits a month, shared by everyone on your network address. Free (a key on a free helious.io account, $0) gets 7 days of history, news 1 hour behind, every price board 60 minutes behind, and 60 calls a minute and 100 credits a month of your own. ONE CREDIT WALLET pays for everything an account does: a data call on any /v1 endpoint or MCP tool is 1 credit, a typed Ask Helious question in the terminal is 10, and on Free, Squawk and Starter the query fresh=1 (fresh: true as an MCP tool argument) answers that one call live for 5 credits. /v1/me, /v1/access, the MCP handshake, get_access_info, list_series, every error and every refusal are free; a keyless market wall is free too. Every answer carries X-Credits-Charged and X-Credits-Remaining headers and the same two numbers in meta (credits_charged, credits_left), and an empty wallet is a 429 with code out_of_credits carrying credits_left, resets_on, next_step (one sentence to relay), the packs that top it up (500 for $9.99, 1,500 for $24.99, never expiring) and upgrade_url: two ways on, a pack or a plan, and the person who owns the key chooses. Not on Pro and need one call live? Add fresh=1 to that request (fresh: true in an MCP tool''s arguments) and it answers live for 5 credits. Each delayed stream snapshot takes one credit on Free and with no key; a paid plan''s stream takes none. Starter ($14.99/mo or $135/yr) gets 12 months of history, live news and prints, every price board 60 minutes behind (live for 5 credits a call with fresh=1), 1,500 credits a month, at 90 calls a minute. Pro ($39.99/mo or $360/yr) gets 24 months of history, 3,000 credits a month and everything live for 1 credit (yields, treasuries, commodities, equities, FX, volatility, correlations) at 120 calls a minute, the streaming WebSocket included. Ultimate ($99/mo or $891/yr) gets 10 years of history, everything live, no credit cap, commercial use and redistribution, 300 calls a minute and the live stream on 5 connections a key. The stream at wss://api.helious.io/v1/stream is open on every tier, key or no key: below Pro it runs the delayed lane (one snapshot a minute, prices and the ranked NASDAQ-100 board 60 minutes behind, news on the plan''s own delay), and Pro and Ultimate run the live lane (every price tick, print and NASDAQ-100 update pushed the moment it happens, on up to 2 connections a key on Pro and 5 on Ultimate), in identical message shapes, so a stream integration survives the upgrade untouched. Authenticate with the same hel_ key sent as the ''Authorization: Bearer hel_...'' header, never a query parameter; the socket sends a hello whose mode field names your lane, feed items in the /v1/feed shape, price ticks, the ranked NASDAQ-100 board, daily official closes and the Helious momentum score, and answers ''ping'' with pong. Keys are sent as ''Authorization: Bearer hel_...''; GET /v1/access returns the ladder and the exact upgrade steps in plain words. There is also an MCP server at https://api.helious.io/mcp: point any MCP client at that URL and the same data arrives as tools.'
  x-stream: 'wss://api.helious.io/v1/stream is the live WebSocket, which OpenAPI cannot describe as a path. One socket on every plan: live on Pro (2 connections a key) and Ultimate (5), delayed below Pro (one snapshot a minute). Messages: hello (mode names the lane), feed (items in the /v1/feed shape; a release print is kind post, category release, with the actual, forecast, previous and sigma in its text), prices, ndx, market_data, score (the Helious momentum score when it moves, in the /v1/score shape), and pong to a ping. The hel_ key goes in the Authorization: Bearer header, never a query parameter; no key opens the delayed lane. Documented at https://helious.io/developers/#stream and https://helious.io/developers/economic-calendar-api/#stream.'
  contact:
    name: Helious support
    email: support@helious.news
    url: https://helious.io/contact
  termsOfService: https://helious.news/terms
servers:
- url: https://api.helious.io
tags:
- name: Reference
  description: Glossary, the measured capture latency and supporting reference data.
paths:
  /api/seo/glossary-index:
    get:
      tags:
      - Reference
      summary: Market glossary terms
      description: Every term in the Helious learn glossary with its slug; full entries render at https://helious.io/learn/{slug}.
      responses:
        '200':
          description: Glossary index
          content:
            application/json:
              schema:
                type: object
      operationId: getApiSeoGlossaryIndex
      x-operation-id-source: derived
  /api/seo/latency-stats:
    get:
      tags:
      - Reference
      summary: 'Measured US capture latency: median and p90'
      description: 'How fast a US print reaches the platform, measured first-hand: seconds from the scheduled release time to capture, aggregated over the shortest of a 7, 14 or 30 day window that holds enough samples. The same figures the methodology page shows at https://helious.io/methodology. No key and no credit. There is no fixed delivery promise; quote these figures instead. Aggregates only: individual samples are not published. When no window clears the minimum sample count the body is {"samples": 0} and the other fields are absent.'
      responses:
        '200':
          description: Capture latency
          content:
            application/json:
              schema:
                type: object
                required:
                - samples
                properties:
                  samples:
                    type: integer
                    description: Prints measured in the window. 0 when no window holds enough samples, and then the other fields are absent.
                  median_seconds:
                    type: number
                    description: Median seconds from the scheduled release time to capture.
                  p90_seconds:
                    type: number
                    description: Ninetieth percentile, in seconds.
                  window_days:
                    type: integer
                    enum:
                    - 7
                    - 14
                    - 30
                    description: The window the figures cover.
      operationId: getApiSeoLatencyStats
      x-operation-id-source: derived
components:
  securitySchemes:
    helious_key:
      type: http
      scheme: bearer
      description: 'Your Helious API key, like hel_xxx, made on your helious.io account page (Account, then API keys). Every /v1 endpoint also works with no key at the sample tier: 1 day of history, news 1 hour behind, no market prices. A free account key gets 7 days and a rate budget of your own. Starter ($14.99/mo) takes the news live, reaches 12 months back and adds the Treasury curve 60 minutes behind; Pro ($39.99/mo) makes every price live with 24 months of history, the /v1/stream WebSocket included; Ultimate ($99/mo) reaches 10 years, allows commercial use and holds the live stream on 5 connections a key (Pro holds 2).'
    helious_oauth:
      type: oauth2
      description: Sign the person in instead of asking them for a key. Dynamic client registration is open, so your client can enrol itself; the one human step is the consent screen. Access tokens last an hour; ask for offline_access to get a rotating refresh token. Full details at https://helious.io/auth.md.
      flows:
        authorizationCode:
          authorizationUrl: https://helious.io/oauth/authorize
          tokenUrl: https://api.helious.io/oauth/token
          refreshUrl: https://api.helious.io/oauth/token
          scopes:
            market:read: Read Helious market data at that plan level.
            account:read: See which plan the account is on.
            openid: Confirm the account identity to your app.
            offline_access: Get a refresh token so you stay connected.