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

# State Verification

> The localhost client handles state verification through the LightClientModule interface methods VerifyMembership and VerifyNonMembership by performing read-only operations directly on the core IBC store.

The localhost client handles state verification through the `LightClientModule` interface methods `VerifyMembership` and `VerifyNonMembership` by performing read-only operations directly on the core IBC store.

When verifying channel state in handshakes or processing packets the `09-localhost` client can simply compare bytes stored under the standardized key paths defined by [ICS-24](https://github.com/cosmos/ibc/tree/main/spec/core/ics-024-host-requirements).

For existence proofs via `VerifyMembership` the 09-localhost client will retrieve the value stored under the provided key path and compare it against the value provided by the caller. In contrast, non-existence proofs via `VerifyNonMembership` assert the absence of a value at the provided key path.

Relayers are expected to provide a sentinel proof when sending IBC messages. Submission of nil or empty proofs is disallowed in core IBC messaging.
The 09-localhost light client module defines a `SentinelProof` as a single byte. Localhost client state verification will fail if the sentinel proof value is not provided.

```go theme={"system"}
var SentinelProof = []byte{0x01
}
```

The `ClientState` of `09-localhost` is stateless, so it is not directly provable with `VerifyMembership` or `VerifyNonMembership`.