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

# Light Client Module interface

> Status must return the status of the client.

## `Status` method

`Status` must return the status of the client.

* An `Active` status indicates that clients are allowed to process packets.
* A `Frozen` status indicates that misbehaviour was detected in the counterparty chain and the client is not allowed to be used.
* An `Expired` status indicates that a client is not allowed to be used because it was not updated for longer than the trusting period.
* An `Unknown` status indicates that there was an error in determining the status of a client.

All possible `Status` types can be found [here](https://github.com/cosmos/ibc-go/blob/v7.0.0/modules/core/exported/client.go#L22-L32).

This field is returned in the response of the gRPC [`ibc.core.client.v1.Query/ClientStatus`](https://github.com/cosmos/ibc-go/blob/v7.0.0/modules/core/02-client/types/query.pb.go#L665) endpoint.

## `TimestampAtHeight` method

`TimestampAtHeight` must return the timestamp for the consensus state associated with the provided height.
This value is used to facilitate timeouts by checking the packet timeout timestamp against the returned value.

## `LatestHeight` method

`LatestHeight` should return the latest block height that the client state represents.

## `Initialize` method

Clients must validate the initial consensus state, and set the initial client state and consensus state in the provided client store.
Clients may also store any necessary client-specific metadata.

`Initialize` is called when a [client is created](https://github.com/cosmos/ibc-go/blob/v7.0.0/modules/core/02-client/keeper/client.go#L30).

## `UpdateState` method

`UpdateState` updates and stores as necessary any associated information for an IBC client, such as the `ClientState` and corresponding `ConsensusState`. See section [`UpdateState`](/ibc/latest/light-clients/developer-guide/updates-and-misbehaviour#updatestate) for more information.

## `UpdateStateOnMisbehaviour` method

`UpdateStateOnMisbehaviour` should perform appropriate state changes on a client state given that misbehaviour has been detected and verified. See section [`UpdateStateOnMisbehaviour`](/ibc/latest/light-clients/developer-guide/updates-and-misbehaviour#updatestateonmisbehaviour) for more information.

## `VerifyMembership` method

`VerifyMembership` must verify the existence of a value at a given commitment path at the specified height. For more information about membership proofs
see the [Existence and non-existence proofs section](/ibc/latest/light-clients/developer-guide/proofs).

## `VerifyNonMembership` method

`VerifyNonMembership` must verify the absence of a value at a given commitment path at a specified height. For more information about non-membership proofs
see the [Existence and non-existence proofs section](/ibc/latest/light-clients/developer-guide/proofs).

## `VerifyClientMessage` method

`VerifyClientMessage` must verify a `ClientMessage`. A `ClientMessage` could be a `Header`, `Misbehaviour`, or batch update.
It must handle each type of `ClientMessage` appropriately. Calls to `CheckForMisbehaviour`, `UpdateState`, and `UpdateStateOnMisbehaviour`
will assume that the content of the `ClientMessage` has been verified and can be trusted. An error should be returned
if the ClientMessage fails to verify. See section [`VerifyClientMessage`](/ibc/latest/light-clients/developer-guide/updates-and-misbehaviour#verifyclientmessage) for more information.

## `CheckForMisbehaviour` method

Checks for evidence of a misbehaviour in `Header` or `Misbehaviour` type. It assumes the `ClientMessage`
has already been verified. See section [`CheckForMisbehaviour`](/ibc/latest/light-clients/developer-guide/updates-and-misbehaviour#checkformisbehaviour) for more information.

## `RecoverClient` method

`RecoverClient` is used to recover an expired or frozen client by updating the client with the state of a substitute client. The method must verify that the provided substitute may be used to update the subject client. See section [Implementing `RecoverClient`](/ibc/latest/light-clients/proposals#implementing-recoverclient) for more information.

## `VerifyUpgradeAndUpdateState` method

`VerifyUpgradeAndUpdateState` provides a path to upgrading clients given an upgraded `ClientState`, upgraded `ConsensusState` and proofs for each. See section [Implementing `VerifyUpgradeAndUpdateState`](/ibc/latest/light-clients/developer-guide/upgrades#implementing-verifyupgradeandupdatestate) for more information.