What Is a Blockchain Fork?
A clear explanation of hard forks and soft forks — how blockchain protocol changes happen and what each type means in practice.
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What to remember
- A hard fork is not backward-compatible and can split a network into two chains.
- A soft fork tightens rules while remaining compatible with older, non-upgraded nodes.
- Forks can happen for technical reasons or because of community disagreement.
- A contentious hard fork can result in two separate, independently continuing assets.
Protocols change over time
Blockchain protocols aren't static; they're periodically updated to add features, fix issues, or adjust rules. A fork is what happens when a protocol's rules change, and it comes in two main forms: hard forks and soft forks.
Hard forks: not backward-compatible
A hard fork changes the rules in a way that isn't backward-compatible: nodes running old software reject blocks that follow the new rules, and vice versa. If the network doesn't fully coordinate the upgrade, this can split the chain into two separate networks.
Soft forks: tightening existing rules
A soft fork tightens the existing rules in a way that older nodes still recognize as valid, even without enforcing the new rule themselves. This generally avoids splitting the network, as long as enough of it adopts the change.
Whether old and new nodes can still agree on the same blocks after a rule change, for a hard fork versus a soft fork.
Why forks happen
- To fix a security vulnerability discovered in the existing protocol.
- To add a new feature or capability that requires changing the rules.
- Because the community disagrees on the network's future direction, leading some participants to continue under different rules.
A contentious hard fork can create two separate assets
When a hard fork happens without full community agreement, both the original chain and the new, forked chain can continue to exist independently, each with its own token, its own history from the fork point forward, and its own community. Some well-known cryptocurrencies exist today as the result of exactly this kind of split.
What to remember
- A hard fork is not backward-compatible and can split a network into two chains.
- A soft fork tightens rules while remaining compatible with older, non-upgraded nodes.
- Forks can happen for technical reasons or because of community disagreement.
- A contentious hard fork can result in two separate, independently continuing assets.