> ## Documentation Index > Fetch the complete documentation index at: https://www.helius.dev/docs/llms.txt > Use this file to discover all available pages before exploring further. # preconfSubscribe > Subscribe to scheduled Solana transactions the moment a validator commits to executing them — before they are shredded. Optional server-side filtering by status, region, and accounts. Start a subscription to [Preconfirmations](/docs/pre-confirmations/overview) — transactions delivered at the scheduled-transaction stage, before they are collected into entries and converted into shreds. This is the lowest-latency transaction signal Helius offers. ## Endpoints `preconfSubscribe` is served from the Helius [Gatekeeper](/docs/gatekeeper/overview) endpoint: * `wss://beta.helius-rpc.com/?api-key=` The `beta` hostname refers to the Gatekeeper rollout, not the maturity of Preconfirmations — it will become the standard endpoint as traffic migrates to Gatekeeper. The stream is not continuous. Coverage scales with the share of network stake forwarding to Helius, so expect slots with no messages — handle these gaps gracefully. See [Coverage](/docs/pre-confirmations/overview#coverage). ## Authorizations Your Helius API key, passed as the `api-key` query parameter. Requires a Professional plan or higher. ## Body Optional. Omit `params` to receive every scheduled transaction. To narrow the stream, pass a filter object as the first element — filtering happens server-side, so you only pay for and receive the transactions you care about. Every field is optional — a missing field means "no constraint" for that predicate, so an empty filter matches every transaction. Set fields combine with **AND**, evaluated in the order `regionInclude` → `accountExclude` → `accountRequired` → `accountInclude`. `false` drops failed (reverted) transactions; success and unknown-status transactions still pass. `true` — like omitting the field — keeps every status. If non-empty, the transaction must originate from **one of** these [regions](#region-codes). Transactions without region information are dropped when this is set. If non-empty, the transaction must reference **at least one** of these accounts (base58 pubkeys). Capped at 500 entries. The transaction is dropped if it references **any** of these accounts. Takes precedence over `accountInclude`. Capped at 500 entries. The transaction must reference **all** of these accounts. Capped at 500 entries. An invalid account value or unrecognized region code returns JSON-RPC error `-32602` (invalid params). Account filters match more than the transaction's static account keys — Helius resolves v0 [address lookup tables](/docs/glossary#address-lookup-table-alt) server-side, so `accountInclude`, `accountExclude`, and `accountRequired` also match accounts a transaction loads through an ALT. ### Region codes | Code | Location | Code | Location | | ----- | -------------- | ----- | ----------- | | `slc` | Salt Lake City | `tyo` | Tokyo | | `fra` | Frankfurt | `ams` | Amsterdam | | `lon` | London | `dal` | Dallas | | `pit` | Pittsburgh | `dub` | Dublin | | `sgp` | Singapore | `mia` | Miami | | `ewr` | Newark | `lax` | Los Angeles | | `iad` | Ashburn | `sea` | Seattle | ## Response Subscription id (needed to unsubscribe) ```json Request theme={"system"} { "jsonrpc": "2.0", "id": 1, "method": "preconfSubscribe", "params": [ { "failed": false, "regionInclude": ["ewr", "fra"], "accountInclude": ["9WzDXwBbmkg8ZTbNMqUxvQRAyrZzDsGYdLVL9zYtAWWM"] } ] } ``` ```javascript JavaScript theme={"system"} const WebSocket = require('ws'); const ws = new WebSocket('wss://beta.helius-rpc.com/?api-key='); ws.on('open', () => { ws.send(JSON.stringify({ jsonrpc: '2.0', id: 1, method: 'preconfSubscribe' // Optional filter: // params: [{ failed: false, accountInclude: ['9WzDXwBbmkg8ZTbNMqUxvQRAyrZzDsGYdLVL9zYtAWWM'] }] })); setInterval(() => ws.ping(), 30_000); }); ws.on('message', (data, isBinary) => { // The subscribe acknowledgement arrives as a JSON text frame if (!isBinary) { const msg = JSON.parse(data.toString()); if (msg.id === 1) console.log('Subscribed, ID:', msg.result); return; } // Notifications arrive as binary frames: // version (u8) | slot (u64 LE) | tx_index (u64 LE) | status (u8) | bincode(VersionedTransaction) const buf = Buffer.from(data); const version = buf.readUInt8(0); if (version !== 1) return; // unknown schema version; update your decoder const slot = buf.readBigUInt64LE(1); const txIndex = buf.readBigUInt64LE(9); const status = buf.readUInt8(17); // 0 = failed, 1 = success, 2 = unknown const txBytes = buf.subarray(18); // bincode-serialized VersionedTransaction console.log('Scheduled transaction:', { slot, txIndex, status, bytes: txBytes.length }); }); ``` ```json Response theme={"system"} { "jsonrpc": "2.0", "id": 1, "result": 24040 } ``` ```text Notification (binary frame) theme={"system"} version u8 payload schema version, currently 1 slot u64 (LE) slot the transaction is scheduled in tx_index u64 (LE) index of the transaction within the slot status u8 0 = failed, 1 = success, 2 = unknown tx bincode bytes bincode(VersionedTransaction) ``` ## Notifications After the JSON acknowledgement, notifications are delivered as **binary** WebSocket frames (not JSON). Each frame is a packed byte layout carrying a single scheduled transaction: | Bytes | Field | Type | Description | | ----- | ------------- | ------------------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------- | | 0 | `version` | `u8` | Payload schema version. Currently `1`. | | 1–8 | `slot` | `u64` (little-endian) | The slot the transaction is scheduled in. | | 9–16 | `tx_index` | `u64` (little-endian) | Index of the transaction within the slot. | | 17 | `status` | `u8` | Transaction status: `0` = failed, `1` = success, `2` = unknown. Execution status is reported by validators on a best-effort basis — `2` when it's unavailable. | | 18+ | `transaction` | `bincode(VersionedTransaction)` | The scheduled transaction, bincode-serialized. | Read the fields in order, then [`bincode`](https://docs.rs/bincode)-deserialize the remaining bytes into a `VersionedTransaction` to read instructions, accounts, and the signature. **Always read and check the `version` byte first.** It is currently `1`. If Helius needs to update the payload format, the version will increment — branch on it so your decoder keeps working across schema changes. A preconfirmation is an early signal, not a guarantee. The transaction has not yet landed onchain and could still fail or be dropped. Confirm landing through standard commitment checks before treating it as final. ## Pricing Preconfirmations require a **Professional plan or higher** and cost **10 credits per message** — one message per streamed transaction. See [Credits](/docs/billing/credits) for details. ## Related What Preconfirmations are and where they sit in the validator pipeline. Stop a subscription by its id.