Key Takeaways
Tendermint is an open-source blockchain engine that handles consensus and networking, allowing developers to build the application layer in any programming language.
It uses a Byzantine Fault Tolerant (BFT) Proof of Stake consensus model with instant transaction finality, meaning no block confirmations are required.
The Application Blockchain Interface (ABCI) separates the consensus engine from the application layer, making the architecture modular and flexible.
The Cosmos SDK builds on Tendermint (now maintained as CometBFT) and powers the Inter-Blockchain Communication (IBC) protocol, enabling cross-chain interoperability across hundreds of chains.
In April 2025, IBC v2 (Eureka) launched on the Cosmos Hub, extending native interoperability to Ethereum without third-party bridges.
Introduction
The blockchains you know and use have a fairly rigid structure. As a developer, this typically gives two options: build applications inside a restrictive environment or fork the code and create a new chain. Creating a new chain is not straightforward, though, since you also need to bootstrap a network and decide on a consensus mechanism.
Tendermint is open-source software that simplifies this process. It provides a ready-made consensus and networking layer so developers can focus on building their application layer in any programming language.
What You Need to Know About Tendermint
Understanding blockchain architecture
Tendermint is a type of blockchain stack, much like Bitcoin and Ethereum. A blockchain stack is not just the database itself but also the peer-to-peer network of nodes, the way they communicate, and the transaction and smart contract logic on top. The goal is for all participants to agree on a shared state, even without trusting each other.
Many major blockchains today rely on a monolithic architecture, in which software components are tightly interconnected. Changing one part risks breaking others. Tendermint takes the opposite approach with modular architecture, separating components so each can be updated independently.
Byzantine fault tolerance (BFT)
Bitcoin solved a long-standing distributed systems problem known as the Byzantine Generals' Problem. Our article on Byzantine fault tolerance covers the details, but in short, BFT describes a system where participants can reach agreement even when some nodes are sending false or corrupted messages.
A blockchain that is not Byzantine fault-tolerant cannot function reliably without a central coordinator. Bitcoin addressed this using a Proof of Work (PoW) consensus algorithm. Tendermint uses a different approach.
The three layers of a blockchain
Blockchains are typically composed of three layers: the application layer, the consensus layer, and the networking layer. The consensus and networking layers are where nodes communicate and agree on a shared state. The application layer is where users and developers interact through decentralized applications and smart contract logic.
Tendermint handles the consensus and networking layers directly. The application layer is left entirely to the developer.
Tendermint Core
A quick note on terminology: Tendermint refers to both the original company (founded by Jae Kwon) and its software. Tendermint Core is the name of the consensus engine. In 2023, Tendermint Core was rebranded to CometBFT to reflect its broader adoption beyond the Cosmos ecosystem. The two names are effectively interchangeable when referring to the protocol.
CometBFT (formerly Tendermint Core) is a distributed consensus engine with Byzantine fault tolerance. It uses a Proof of Stake (PoS) mechanism where a random validator from the active set is selected each round to propose the next block. If enough of the other validators approve, the block is added, and finality is immediate. There is no need to wait for confirmations, unlike Bitcoin or Ethereum.
So long as at least two-thirds of validators are honest, the network continues to operate correctly. CometBFT is designed to handle 1,000 to 10,000 transactions per second with sub-six-second finality.
The Application Blockchain Interface (ABCI)
What makes Tendermint particularly useful for developers is the Application Blockchain Interface, or ABCI. This is the interface that connects the consensus engine to whatever application layer the developer has built. Because the ABCI is a defined standard, developers can write their application in any programming language and connect it to the consensus engine without modifying it.
This means a developer building a new blockchain does not need to implement consensus from scratch or bootstrap a validator network. They define their application logic and plug it into the stack.
What happened to Ethermint?
An early example of what was possible with Tendermint was Ethermint, a project that took the Ethereum Virtual Machine and connected it to Tendermint Core. This made it possible to run Solidity smart contracts on a Proof of Stake chain. Ethermint has since been superseded by Evmos and by the open-sourced Cosmos EVM, which Cosmos Labs released in 2025. The idea behind Ethermint, which is combining Ethereum-compatible execution with a faster and more energy-efficient consensus layer, remains central to the Cosmos ecosystem.
Blockchain Interoperability and the Cosmos SDK
The Cosmos SDK is an open-source framework built on top of CometBFT. It allows developers to create application-specific public or private blockchains. These chains can connect to the wider Cosmos network via the Inter-Blockchain Communication (IBC) protocol, which enables asset transfers and message passing between chains without requiring a centralized bridge. This is what many refer to as an "internet of blockchains." The interoperability it offers has attracted significant developer interest.
In April 2025, IBC v2, also known as IBC Eureka, launched on the Cosmos Hub. This upgrade extended native IBC connectivity to Ethereum, allowing users to transfer assets between Cosmos chains and Ethereum without third-party bridges. It supports over $3 billion in monthly cross-chain volume across more than 115 blockchains. For more on the broader ecosystem, see What Is Cosmos (ATOM)?.
Well-known projects built with the Cosmos SDK include BNB Smart Chain, Osmosis, dYdX, and Injective. These projects illustrate the range of use cases the framework supports, from decentralized exchanges to derivatives platforms and application-specific financial chains.
FAQ
What is the difference between Tendermint and CometBFT?
They refer to the same consensus engine. Tendermint Core was rebranded to CometBFT in 2023 to reflect its independent development and use beyond the original Cosmos project. The underlying protocol and its BFT Proof of Stake mechanics are unchanged.
Is Tendermint the same as Cosmos?
No. Tendermint (CometBFT) is the consensus engine that powers the Cosmos SDK, but they are separate components. Cosmos is a broader ecosystem of interoperable blockchains. Tendermint provides the consensus and networking layer that Cosmos chains can use.
How does Tendermint achieve instant finality?
Tendermint uses a round-based validator voting process. Once two-thirds of validators sign off on a block, it is considered final. There is no probabilistic finality and no risk of the chain reorganizing, which means transactions are confirmed in a single block.
What is ABCI?
The Application Blockchain Interface (ABCI) is a standard interface that connects the Tendermint consensus engine to an application layer. Because the interface is language-agnostic, developers can write their application in any programming language and still benefit from Tendermint's consensus and networking stack.
What is IBC v2 (Eureka)?
IBC v2, launched in April 2025, is an upgrade to the Inter-Blockchain Communication protocol that enables native connectivity between Cosmos chains and Ethereum. It removes the need for third-party bridges and supports asset transfers and message passing directly between the two ecosystems.
Closing Thoughts
Tendermint solves a common problem in blockchain development: how to build a new chain without reinventing consensus from scratch. By separating the consensus and networking layers from the application layer through the ABCI, it gives developers a modular, language-agnostic foundation to work from. CometBFT carries that architecture forward, and the Cosmos SDK has turned it into a practical toolkit powering some of the most active chains in the industry.
Further Reading
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