> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cosmos.network/llms.txt
> Use this file to discover all available pages before exploring further.

# Subscribing to events via Websocket

CometBFT emits different events, which you can subscribe to via
[Websocket](https://en.wikipedia.org/wiki/WebSocket). This can be useful
for third-party applications (for analysis) or for inspecting state.

[List of events](https://godoc.org/github.com/cometbft/cometbft/types#pkg-constants)

To connect to a node via websocket from the CLI, you can use a tool such as
[wscat](https://github.com/websockets/wscat) and run:

```sh theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
wscat -c ws://127.0.0.1:26657/websocket
```

NOTE: If your node's RPC endpoint is TLS-enabled, utilize the scheme `wss` instead of `ws`.

You can subscribe to any of the events above by calling the `subscribe` RPC
method via Websocket along with a valid query.

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
    "jsonrpc": "2.0",
    "method": "subscribe",
    "id": 0,
    "params": {
        "query": "tm.event='NewBlock'"
    }
}
```

Check out [API docs](https://docs.cometbft.com/v0.37/rpc/) for
more information on query syntax and other options.

You can also use tags, given you had included them into DeliverTx
response, to query transaction results. See [Indexing
transactions](/cometbft/v0.37/docs/app-dev/indexing-transactions) for details.

## Query parameter and event type restrictions

While CometBFT imposes no restrictions on the application with regards to the type of
the event output, there are several restrictions when it comes to querying
events whose attribute values are numeric.

* Queries cannot include negative numbers
* If floating points are compared to integers, they are converted to an integer
* Floating point to floating point comparison leads to a loss of precision for very big floating point numbers
  (`10000000000000000000.0` is treated the same as `10000000000000000000.6`)
* When floating points do get converted to integers, they are not rounded, the decimal part is simply truncated.
  This has been done to preserve the behaviour present before introducing the support for BigInts in the query parameters.

## ValidatorSetUpdates

When validator set changes, ValidatorSetUpdates event is published. The
event carries a list of pubkey/power pairs. The list is the same
CometBFT receives from ABCI application (see [EndBlock
section](https://github.com/cometbft/cometbft/blob/v0.37.x/spec/abci/abci++_methods.md#endblock) in
the ABCI spec).

Response:

```json theme={"theme":{"light":"github-light-high-contrast","dark":"github-dark-high-contrast"}}
{
    "jsonrpc": "2.0",
    "id": 0,
    "result": {
        "query": "tm.event='ValidatorSetUpdates'",
        "data": {
            "type": "tendermint/event/ValidatorSetUpdates",
            "value": {
              "validator_updates": [
                {
                  "address": "09EAD022FD25DE3A02E64B0FE9610B1417183EE4",
                  "pub_key": {
                    "type": "tendermint/PubKeyEd25519",
                    "value": "ww0z4WaZ0Xg+YI10w43wTWbBmM3dpVza4mmSQYsd0ck="
                  },
                  "voting_power": "10",
                  "proposer_priority": "0"
                }
              ]
            }
        }
    }
}
```