# Source: https://gofastmcp.com/python-sdk/fastmcp-server-event_store.md

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# event_store

# `fastmcp.server.event_store`

EventStore implementation backed by AsyncKeyValue.

This module provides an EventStore implementation that enables SSE polling/resumability
for Streamable HTTP transports. Events are stored using the key\_value package's
AsyncKeyValue protocol, allowing users to configure any compatible backend
(in-memory, Redis, etc.) following the same pattern as ResponseCachingMiddleware.

## Classes

### `EventEntry` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/event_store.py#L26" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

Stored event entry.

### `StreamEventList` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/event_store.py#L34" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

List of event IDs for a stream.

### `EventStore` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/event_store.py#L40" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

EventStore implementation backed by AsyncKeyValue.

Enables SSE polling/resumability by storing events that can be replayed
when clients reconnect. Works with any AsyncKeyValue backend (memory, Redis, etc.)
following the same pattern as ResponseCachingMiddleware and OAuthProxy.

**Args:**

* `storage`: AsyncKeyValue backend. Defaults to MemoryStore.
* `max_events_per_stream`: Maximum events to retain per stream. Default 100.
* `ttl`: Event TTL in seconds. Default 3600 (1 hour). Set to None for no expiration.

**Methods:**

#### `store_event` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/event_store.py#L94" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
store_event(self, stream_id: StreamId, message: JSONRPCMessage | None) -> EventId
```

Store an event and return its ID.

**Args:**

* `stream_id`: ID of the stream the event belongs to
* `message`: The JSON-RPC message to store, or None for priming events

**Returns:**

* The generated event ID for the stored event

#### `replay_events_after` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/event_store.py#L135" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
replay_events_after(self, last_event_id: EventId, send_callback: EventCallback) -> StreamId | None
```

Replay events that occurred after the specified event ID.

**Args:**

* `last_event_id`: The ID of the last event the client received
* `send_callback`: A callback function to send events to the client

**Returns:**

* The stream ID of the replayed events, or None if the event ID was not found