Transaction validity
Nodes verify that inputs reference spendable outputs, authorization conditions succeed, values remain in range and no input is spent twice.
A valid transaction can still be non-standard. Relay and mining policy is intentionally stricter and can change without changing consensus.
Block validity
A block must satisfy proof of work, size and weight limits, timestamp constraints, coinbase rules and all transaction-level requirements. Its previous-block reference must connect to valid history.
Precision matters
Consensus implementations must interpret every edge case consistently. A disagreement in validation behavior can split nodes onto incompatible histories, so changes require conservative engineering and extensive testing.
Visual recap
The validation boundary
Policy affects relay; consensus determines whether data can enter the blockchain.
Transaction data
Policy checks
Consensus checks
Block checks
Accept or reject
Key takeaways
- Consensus rules determine validity.
- Relay policy is not the same as consensus.
- Blocks inherit transaction validity requirements.
- Small implementation differences can create serious compatibility risk.
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 node refusing to relay a transaction prove that the transaction is invalid by consensus?
References
