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Light clients are an important part of the complete blockchain system for most applications. CometBFT provides unique speed and security properties for light client applications. See our light package.

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Overview

The objective of the light client protocol is to get a commit for a recent block hash where the commit includes a majority of signatures from the last known validator set. From there, all the application state is verifiable with merkle proofs.

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Properties

  • You get the full collateralized security benefits of CometBFT; no need to wait for confirmations.
  • You get the full speed benefits of CometBFT; transactions commit instantly.
  • You can get the most recent version of the application state non-interactively (without committing anything to the blockchain). For example, this means that you can get the most recent value of a name from the name-registry without worrying about fork censorship attacks, without posting a commit and waiting for confirmations. It’s fast, secure, and free!

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Where to obtain trusted height & hash

Trust Options One way to obtain semi-trusted hash & height is to query multiple full nodes and compare their hashes: 
$ curl -s https://233.123.0.140:26657:26657/commit | jq "{height: .result.signed_header.header.height, hash: .result.signed_header.commit.block_id.hash}"
{
  "height": "273",
  "hash": "188F4F36CBCD2C91B57509BBF231C777E79B52EE3E0D90D06B1A25EB16E6E23D"
}

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Running a light client as an HTTP proxy server

CometBFT comes with a built-in cometbft light command, which can be used to run a light client proxy server, verifying CometBFT RPC. All calls that can be tracked back to a block header by a proof will be verified before passing them back to the caller. Other than that, it will present the same interface as a full CometBFT node. You can start the light client proxy server by running cometbft light <chainID>, with a variety of flags to specify the primary node, the witness nodes (which cross-check the information provided by the primary), the hash and height of the trusted header, and more. For example: 
$ cometbft light supernova -p tcp://233.123.0.140:26657 \
  -w tcp://179.63.29.15:26657,tcp://144.165.223.135:26657 \
  --height=10 --hash=37E9A6DD3FA25E83B22C18835401E8E56088D0D7ABC6FD99FCDC920DD76C1C57
For additional options, run cometbft light --help.