> ## Documentation Index > Fetch the complete documentation index at: https://finance.dev/llms.txt > Use this file to discover all available pages before exploring further. # Stream Live Prices > Streams live bids, trades, and last prices for prediction-market contracts as server-sent events. **Use Case:** Show a contract's latest YES and NO prices and update them as orders and trades arrive, without polling. **What this stream gives you.** Open one HTTP connection and the server keeps it open, pushing each contract's latest price, every new bid, and every trade as they happen. It uses [server-sent events](https://developer.mozilla.org/en-US/docs/Web/API/Server-sent_events): a browser reads it with `EventSource`, and any HTTP client can read it line by line. ## Request ```text theme={null} GET /v1/predictions/stream?symbols=HORC_1126_Democratic,HORC_1126_Republican GET /v1/predictions/stream?events=HORC_1126 ``` | Parameter | Description | | - | - | | `symbols` | Contract symbols, comma-separated or repeated (`symbols=A&symbols=B`). | | `events` | Event IDs, comma-separated or repeated. Streams every `ACTIVE` contract under each event. | Send `symbols`, `events`, or both; duplicates are removed. A connection can carry up to **200** contracts, counted after events are expanded. Event IDs come from [Search](/api-reference/predictions/search) with `type=events`, or from a contract's `eventId`. [Get Event Contracts](/api-reference/predictions/get-event-contracts) lists the contracts an event expands to. An event is expanded once, when you connect: a contract listed under it later is not added until you reconnect. ## Events ForecastEx takes **buy orders only**. Every order is a bid, for YES or for NO, so there is no ask. | Event | When | Payload | | - | - | - | | `subscribed` | First, once | Every contract on the stream, and each requested event's contracts | | `snapshot` | Once per contract, before anything else for it | Each outcome's last trade, and the contract's statistics | | `bid` | Each new YES or NO bid | The order as the venue received it | | `trade` | Each trade | One leg of a match | | `stats` | Whenever the contract's statistics change | The `contract` block alone | | `gap` | When you fell too far behind | The contract whose bids or trades you missed. A fresh `snapshot` follows. | A `: ping` comment is sent every 15 seconds to keep idle connections open. ### subscribed ```json theme={null} { "symbols": ["HORC_1126_Democratic", "HORC_1126_Republican"], "events": { "HORC_1126": ["HORC_1126_Democratic", "HORC_1126_Republican"] } } ``` `events` is present only when you asked for events. ### snapshot ```json theme={null} { "symbol": "HORC_1126_Democratic", "yes": { "last": "0.50", "lastSize": "1" }, "no": { "last": "0.50", "lastSize": "1" }, "contract": { "high": "0.63", "low": "0.47", "settlement": "0.37", "volume": "123", "notional": "69.69", "openInterest": "54886", "tradingSession": "OPEN" }, "receivedAtUnixMs": 1791499255775 } ``` | Field | Notes | | - | - | | `yes`, `no` | Each outcome's last trade price and size. `null` for an outcome that has not traded. | | `contract.volume` | Contracts matched in the session. One match is one contract, even though it prints as two trades. | | `contract.notional` | Total value traded in the session. | | `contract.openInterest` | Open contracts. | | `contract.high`, `low`, `settlement` | Session high, low, and settlement price. | | `contract.tradingSession` | The venue's state for the contract, such as `OPEN`, `HALTED`, or `CLOSED`. | The venue reports a contract's last trade without saying which outcome it was for. The snapshot reads it as the YES price and sets NO to `1.00` minus it. After the first live trade, `yes` and `no` come from tagged trades. ### bid ```json theme={null} { "symbol": "HORC_1126_Democratic", "outcome": "NO", "price": "0.62", "size": "1", "orderId": "CZ1P1MS4A1C1", "placedAtUnixNs": 1791499265208000000, "receivedAtUnixMs": 1791499265211 } ``` A bid is sent when it is placed. Its later fills and cancellation are not sent, so a `bid` event does not mean the order is still resting. ### trade ```json theme={null} { "symbol": "HORC_1126_Democratic", "outcome": "NO", "price": "0.53", "size": "1", "tradeId": "CZKNTJJXE1DD", "aggressorSide": "Buy", "tradeTimeUnixNs": 1791499265208000000, "receivedAtUnixMs": 1791499265211 } ``` A match is a YES buyer and a NO buyer, so every match arrives as **two** `trade` events with the same `tradeId`: one for each outcome, at prices that add up to `1.00`. Count matches by `tradeId`, not by event. ### stats ```json theme={null} { "symbol": "HORC_1126_Democratic", "contract": { "high": "0.63", "low": "0.47", "settlement": "0.37", "volume": "124", "notional": "70.16", "openInterest": "54887", "tradingSession": "OPEN" } } ``` Each `stats` replaces the last. A match usually sends two: volume and notional change with the trade, and open interest follows. A new last price on its own sends no `stats`, because the `trade` events already carry it. ### Contracts from events For a contract you subscribed to through `events`, every `snapshot`, `bid`, `trade`, `stats`, and `gap` also carries `eventId`: ```json theme={null} { "symbol": "HORC_1126_Democratic", "eventId": "HORC_1126", "outcome": "NO", "price": "0.62", "size": "1" } ``` ## Ordering * For each contract, `snapshot` comes first, and nothing else is sent for that contract before it. * After that, `bid`, `trade`, and `stats` arrive in the order the venue sent them, and a match's two trades come before the `stats` they moved. * Events for different contracts interleave. If the contract is already being streamed, its snapshot is sent at once. Otherwise it arrives once the venue answers, usually within about a second. ## Reconnecting Events have no IDs and are not replayed. When you reconnect, as `EventSource` does on its own, you receive a new `subscribed` and a fresh `snapshot` for every contract. Bids and trades sent while you were disconnected are lost, but the snapshot's prices and statistics show where the market is now. ## Examples ```bash cURL theme={null} curl -N "https://api.aries.com/v1/predictions/stream?events=HORC_1126" ``` ```javascript Browser theme={null} const stream = new EventSource( "https://api.aries.com/v1/predictions/stream?symbols=HORC_1126_Democratic" ); stream.addEventListener("snapshot", (e) => { const { symbol, yes, no, contract } = JSON.parse(e.data); console.log(symbol, "YES", yes.last, "NO", no.last, "volume", contract.volume); }); stream.addEventListener("trade", (e) => { const { symbol, outcome, price, size } = JSON.parse(e.data); console.log(symbol, outcome, "traded", size, "@", price); }); stream.addEventListener("bid", (e) => { const { symbol, outcome, price, size } = JSON.parse(e.data); console.log(symbol, "new", outcome, "bid", size, "@", price); }); ``` ## Working with the stream * **Prices are decimal strings.** `"0.53"`, not `0.53`. Parse them with a decimal type. * **A missing value is `null`, not zero.** A `null` last price means the outcome has not traded. * **Do not put the stream behind a buffering proxy.** Events must reach you as they are sent. ## Errors Errors are returned before the stream opens, in the usual [error envelope](/prediction-api/overview#response-envelope): | Status | `code` | When | | - | - | - | | `400` | `MISSING_SYMBOLS` | Neither `symbols` nor `events` names anything | | `400` | `TOO_MANY_SYMBOLS` | More than 200 contracts after events are expanded | | `400` | `INVALID_SYMBOL` | A symbol containing whitespace, `*`, or `>`, or with a leading or trailing dot | | `400` | `UNKNOWN_EVENT` | An event ID that does not exist | | `400` | `NO_LIVE_CONTRACTS` | An event with no `ACTIVE` contract | | `503` | `SHUTTING_DOWN` | The server is restarting; reconnect | An unknown **symbol** is not an error. It never receives a snapshot. 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