TL;DR: A chain halt occurs when a blockchain stops producing new blocks entirely. Unlike congestion, where the network slows down but keeps running, a chain halt means zero new transactions are being confirmed and the network is effectively frozen. Chain halts are caused by consensus failures, critical client bugs, DDoS attacks on validators, resource exhaustion, or failed upgrades. They are among the most severe incidents a blockchain can experience because every application, wallet, and protocol built on that chain becomes unusable until the network resumes. Recovery requires coordinated action across the validator set, typically involving identifying the root cause, deploying a patch, and restarting consensus.
The Simple Explanation
A chain halt is the blockchain equivalent of a complete server outage. When a traditional web application's server goes down, no one can access the service. When a blockchain halts, no one can send transactions, claim yields, close positions, or interact with any smart contract on the network. The chain simply stops advancing.
The distinction between congestion and a halt is important. During congestion, blocks are still being produced and transactions are still being confirmed, just more slowly and at higher cost. Users compete for limited block space, but the network is functional. During a chain halt, there are no blocks being produced at all. The network has stopped. Transactions sit in the mempool with no possibility of confirmation until the chain resumes.
For end users, a chain halt means wallets show balances but cannot send or receive funds. DeFi positions cannot be adjusted, which is especially dangerous during volatile market conditions when users might need to add collateral or close leveraged positions. NFT auctions freeze mid-bid. Bridges stop processing transfers. Every application built on the chain is effectively offline.
Common Causes of Chain Halts
Consensus failures are the most frequent cause of chain halts. A blockchain produces new blocks through its consensus mechanism, which requires a minimum threshold of validators to agree on the next block. On many Proof of Stake chains, this threshold is two-thirds of the staked validator weight. If enough validators go offline, crash, or become unable to communicate with each other, the network cannot reach consensus, and block production stops.
