Competing tips
Two valid blocks may be found near the same time, leaving parts of the network on different tips. Nodes continue validating and miners extend the tip they currently consider best.
Once one branch gains more chainwork, nodes on the other branch disconnect its blocks and connect the stronger valid branch.
Transaction effects
Transactions from disconnected blocks may appear in the winning branch, return to the mempool if still valid, or conflict with transactions that are now confirmed. Applications therefore treat confirmation depth as risk reduction, not an absolute promise.
Operational response
Wallets and services should monitor block hashes as well as heights, handle confirmation reversals and avoid assuming every reorganisation is an attack. Short natural reorganisations are possible in normal mining.
Chain reorganisations
Nodes follow the valid chain with the most accumulated work
Compare two competing branches and see what changes when one becomes the best-work chain.
Shared history
Both candidate chains descend from the same previously accepted block.
Key vocabulary
Terms worth knowing
- Competing tip
- A valid block at the same or nearby height that creates an alternative chain ending.
- Reorganisation
- A change of active chain when a different valid branch gains more accumulated work.
- Disconnected transaction
- A transaction removed from the active chain that may return to the mempool if still valid and unconfirmed.
Worked example
Two miners find blocks nearly together
Different regions receive different valid blocks first. For a short period, nodes can follow different tips without disagreeing about the rules.
- 1Each node validates the block it receives
- 2Mining temporarily continues on both tips
- 3A later block gives one branch more chainwork
- 4Nodes validate and activate that branch
- 5Transactions from the disconnected block are reconsidered
Temporary tip disagreement is an expected distributed-systems event; confirmations measure increasing settlement confidence rather than mathematical irreversibility.
Common misconceptions
What learners often get wrong
Misconception
A reorganisation means Bitcoin's rules changed.
More accurate
Ordinary reorganisations choose between competing valid histories under the same rules.
Misconception
A transaction removed by a reorg is always lost.
More accurate
If it remains valid and non-conflicting, it can return to mempools and confirm in a later block.
Try it yourself
Trace a two-block reorganisation.
- Draw old and competing branches
- Mark their chainwork
- Identify disconnected and connected blocks
- Classify each affected transaction as valid, conflicting or already confirmed elsewhere
Use fictional values and public information only. Never enter seed words, private keys or other wallet secrets into a learning exercise.
Key takeaways
- Chainwork, not block count alone, selects the active chain.
- Disconnected transactions may return to the mempool.
- More confirmations generally reduce reorganisation risk.
- Applications must handle a block changing status.
Lesson recap
Check what you learned
Reveal each model answer, then honestly mark whether you understood it or need another review.
1 of 3
Recall
Does a reorganisation make every transaction in the disconnected blocks invalid?
References
