A soft fork tightens rules in a way old software still accepts. New blocks remain valid to old nodes because the new rules are a subset of the old ones. Not every node must upgrade at once. You avoid a guaranteed chain split.
Bitcoin's SegWit was a soft fork that changed how signatures are stored and freed block space. Ethereum's London upgrade added a fee burn while legacy clients could still follow the chain. Developers can ship new rules without abandoning old wallets. For most users the change is invisible. A soft fork changes a blockchain's rules in a way that remains backward-compatible with older software.
This lets the network upgrade without forcing every participant to update simultaneously. Blocks created under the new rules are still valid to old nodes, because the new rules are a stricter subset of the old ones. A soft fork tightens rules so old nodes still see new blocks as valid. SegWit on Bitcoin was a soft fork.
Soft Fork Visualization
Explore how soft forks maintain backward compatibility, allowing network upgrades without forcing all nodes to update simultaneously.
Original Network
All nodes follow the same rules. Old blocks are accepted by all nodes.