⚙️ Tendermint Tendermint / CometBFT
A ready-made open-source engine that handles a blockchain's hardest plumbing (agreeing on transactions and talking between computers) so builders can add their own app on top in any programming language.
🧩 The simple version — a pre-built engine for a blockchain
Building a blockchain from scratch is brutal. The hardest piece is consensus: getting thousands of independent computers to agree on the same list of transactions, in the same order, with no boss in charge. Tendermint hands you that piece already built. You write your app's logic on top, in whatever programming language you like, and the engine takes care of agreeing and gossiping between machines. Think of it like a car engine you drop into your own chassis: you design the bodywork, the engine just runs.
🗳️ How it reaches agreement — a two-round vote
Tendermint's consensus is BFT Proof-of-Stake. A fixed set of stakers called validators take turns proposing the next block. The rest vote in two rounds:
| Round | What happens |
|---|---|
| 🙋 Pre-vote | Validators signal "I've seen this proposed block and it looks valid" |
| ✅ Pre-commit | If enough pre-votes arrived, validators lock in their commitment to the block |
A block only commits once it has approval from more than two-thirds of validators. That high bar is what makes cheating so hard.
🛡️ Byzantine Fault Tolerant up to 1/3
The engine is Byzantine Fault Tolerant: the network keeps working correctly even if up to one-third of validators are offline, buggy, or actively malicious. As long as more than two-thirds are honest and online, the chain moves forward and stays safe.
⚡ Instant finality — no waiting for confirmations
Once a block is committed under Tendermint, it is final and irreversible immediately. This is called deterministic finality. It's different from Bitcoin, where you wait for several more blocks ("confirmations") before a payment is considered settled. With Tendermint, committed means done.
🌌 Where a beginner actually meets it
Tendermint is the foundation of the Cosmos ecosystem. The Cosmos SDK (a toolkit for launching new chains) is built on it, and it powers IBC (Inter-Blockchain Communication), which connects hundreds of chains so they can pass tokens and messages to each other. The piece that makes this modular design work is ABCI (Application Blockchain Interface): the socket that separates the engine from the app, so the app can be written in any language.
You rarely touch Tendermint directly. You meet it through the chains it runs, like Cosmos Hub (ATOM) and other Cosmos-SDK chains such as Celestia and Injective.
📛 Tendermint vs CometBFT — the name change
The engine started as Tendermint Core, co-founded by Jae Kwon. In early 2023 it was forked and rebranded to CometBFT, now maintained by Informal Systems with Cosmos stakeholders. It's the same algorithm lineage, and CometBFT is the actively maintained name most Cosmos chains use today — but you'll still see "Tendermint" all over older documentation.
🚨 Things beginners should know
- 🚫 Not a token — There's nothing called "Tendermint" to buy; it's the engine under chains like Cosmos Hub (ATOM)
- 🧠 Not the same as Cosmos — Cosmos is the ecosystem; Tendermint/CometBFT is the engine it runs on
- 🔁 Two names, one thing — "Tendermint" in old docs and "CometBFT" in new ones describe the same consensus lineage
- 🔢 Fixed validator set — Agreement relies on a known panel of validators, not an open mining race
❓ FAQ
- Is Tendermint a coin I can buy?
- No. Tendermint is infrastructure — an engine that other blockchains run on, not a cryptocurrency. The flagship chain built on it, Cosmos Hub, has a token called ATOM, but there is no 'Tendermint' coin to trade.
- Is Tendermint the same thing as Cosmos?
- No. Cosmos is an ecosystem of connected blockchains; Tendermint (now CometBFT) is the engine many of those chains run on. Cosmos is built on top of Tendermint, so they're related but not the same.
- Why was Tendermint renamed to CometBFT?
- In early 2023 the engine was forked and rebranded to CometBFT, now maintained by Informal Systems with Cosmos stakeholders. It's the same algorithm lineage — most Cosmos chains today use the CometBFT name, but you'll still see 'Tendermint' in older docs.