Fork Detection

Fork detection is the practice of monitoring for unexpected chain splits - times when the network produces two or more competing chains, intentionally or not.

The kinds of forks that get detected:

• Routine 1-2 block reorgs. Happen a few times a year from near-simultaneous block finds. Resolved automatically within a block or two; no operator intervention needed.
• Software-bug forks. A bug in node software accepts an invalid block; nodes running the buggy version follow a different chain than nodes running the correct one. Rare, but BIP 50 is the canonical 2013 example.
• Activation forks. A soft-fork or hard-fork rule change activates, and not all nodes upgrade. Intentional but managed via signaling thresholds and warning periods.
• Contentious hard forks. A faction deliberately changes consensus rules. The 2017 Bitcoin Cash split is the example.

How fork detection works in practice:

• Bitcoin Core's built-in warnings. getblockchaininfo exposes a warnings field that surfaces unusual chain conditions: unexpected high-difficulty competing chains, unknown soft-fork bits set in many recent blocks, etc.
• Cross-source comparison. Compare your node's tip hash to multiple block explorers (mempool.space, blockstream.info, Bitaroo, etc.) plus a few trusted peers. If they disagree at any depth, investigate.
• Forkmonitor.info. A dedicated public service that runs many Bitcoin node implementations side-by-side and alerts on divergence. The canonical fork-watcher service.

Who needs this:

• Exchanges, custodians, payment processors. Confirmation logic depends on being on the correct chain. Freeze deposits or withdrawals if the chain forks.
• Miners. Mining on a minority fork wastes hashing power.
• Large on-chain transactions. Wait for deeper confirmations during any suspected fork event.

Most users never see this in practice. Bitcoin Core handles routine reorgs transparently. The discipline matters for operators of high-value systems where "the wrong chain" would be expensive.