`Event`s are objects that contain information about the execution of the application. They are mainly used by service providers like block explorers and wallet to track the execution of various messages and index transactions. {synopsis}
* A `type` to categorize the Event at a high-level; for example, the Cosmos SDK uses the `"message"` type to filter Events by `Msg`s.
* A list of `attributes` are key-value pairs that give more information about the categorized Event. For example, for the `"message"` type, we can filter Events by key-value pairs using `message.action={some_action}`, `message.module={some_module}` or `message.sender={some_sender}`.
| `tx.height=23` | Query all transactions at height 23 |
| `message.action='/cosmos.bank.v1beta1.Msg/Send'` | Query all transactions containing a x/bank `Send` [Service `Msg`](../building-modules/msg-services.md). Note the `'`s around the value. |
| `message.action='send'` | Query all transactions containing a x/bank `Send` [legacy `Msg`](../building-modules/msg-services.md#legacy-amino-msgs). Note the `'`s around the value. |
| `message.module='bank'` | Query all transactions containing messages from the x/bank module. Note the `'`s around the value. |
| `create_validator.validator='cosmosval1...'` | x/staking-specific Event, see [x/staking SPEC](../../../cosmos-sdk/x/staking/spec/07_events.md). |
You can use Tendermint's [Websocket](https://docs.tendermint.com/master/tendermint-core/subscription.html#subscribing-to-events-via-websocket) to subscribe to Events by calling the `subscribe` RPC method:
The `type` and `attribute` value of the `query` allow you to filter the specific Event you are looking for. For example, a `transfer` transaction triggers an Event of type `Transfer` and has `Recipient` and `Sender` as `attributes` (as defined in the [`events.go` file of the `bank` module](https://github.com/cosmos/cosmos-sdk/blob/v0.42.1/x/bank/types/events.go)). Subscribing to this Event would be done like so:
As previously described, Events are defined on a per-module basis. It is the responsibility of the module developer to define Event types and Event attributes. Except in the `spec/XX_events.md` file, these Event types and attributes are unfortunately not easily discoverable, so the Cosmos SDK proposes to use Protobuf-defined [Typed Events](../architecture/adr-032-typed-events.md) for emitting and querying Events.