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The TON Center Streaming API (v2) provides developer access to TON Blockchain through Server-Sent Events (SSE) and WebSockets. It delivers low-latency, real-time updates on transactions and actions observed on the TON blockchain. Clients can subscribe to updates for monitoring a wallet, some contract addresses, or a specific trace of transactions. Streaming API serves as a real-time, streaming version of the indexed access layer (API v3). Use it when building wallets, explorers, monitoring systems, or automation tools.

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Event groups

The Streaming API emits the following event groups:
  • Trace-based events: transactions, actions, trace
  • State updates: account_state_change and jettons_change
  • Invalidation signal: trace_invalidated
The event types section and notification schemas section provide the exact payload structure for each event.

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Finality model

Trace-based events carry a finality field according to their finality level: 
"finality": "pending" | "confirmed" | "finalized"
Each trace moves through the following monotonic lifecycle:
  • pending — result of emulation or speculative execution. This state can be invalidated (trace_invalidated).
  • confirmed — trace or transactions are included in a candidate shard block. Rollback chance is very small, but still possible.
  • finalized — committed in the masterchain and will not be updated nor invalidated.
Non-trace events behave differently:
  • account_state_change and jettons_change are emitted only when finality field is set to either confirmed or finalized.
  • trace_invalidated applies to previously emitted trace-based data and is not emitted after finalized.

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Delivery behavior

The min_finality field is used to control how early the server emits trace-based updates:
  • pending — receive every trace snapshot as it moves from pending to confirmed to finalized.
  • confirmed — skip pure emulation results and start at confirmed or later.
  • finalized — receive only finalized trace-based events.
Choose the setting based on the tolerance for speculative data:
  • Use pending for the lowest latency.
  • Use confirmed for lower rollback risk with near-real-time delivery.
  • Use finalized when only settled data is acceptable.
The delivery semantics section and event invalidation section document the exact behavior for each event type.

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Supported interfaces

The Streaming API exposes two transports: SSE and a WebSocket. Choose either of the transports to proceed with its usage:

SSE: Server-Sent Events

Recommended for browser environments or clients that prefer HTTP streaming and a fixed subscription.

WebSocket

Preferred for persistent, bidirectional communication with dynamic subscription patterns.

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See also