> ## 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, use 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 [the API docs](/cometbft/next/api-reference/rpc/index) for
more information on query syntax and other options.

You can also use tags, given you have included them in the FinalizeBlock
response, to query transaction results. See [Indexing
transactions](/cometbft/next/docs/app-dev/Indexing-Transactions) for details.

## Query parameter and event type restrictions

While CometBFT imposes no restrictions on the application with regard to the type of
the event output, there are several considerations that need to be taken into account
when querying events with numeric values.

* Queries convert all numeric event values to `big.Float`, provided by `math/big`. Integers
  are converted into a float with a precision equal to the number of bits needed
  to represent this integer. This is done to avoid precision loss for big integers when they
  are converted with the default precision (`64`).
* When comparing two values, if either one of them is a float, the other one will be represented
  as a big float. Integers are again parsed as big floats with a precision equal to the number
  of bits required to represent them.
* As with all floating point comparisons, comparing floats with decimal values can lead to imprecise
  results.
* Queries cannot include negative numbers.

Prior to version `v0.38.x`, floats were not supported as query parameters.

## ValidatorSetUpdates

When the validator set changes, the ValidatorSetUpdates event is published. The
event carries a list of pubkey/power pairs. The list is the same as what
CometBFT receives from the ABCI application (see the [EndBlock
section](https://github.com/cometbft/cometbft/blob/v0.38.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"
                }
              ]
            }
        }
    }
}
```