Hash-linked ledger · interactive lab
What changes after you edit the first block?
Type a character in block 1's Data field. Its SHA256 hash changes, and each later block incorporates the preceding block's new hash. Watch the hash fields and the written validity labels, not just the colors.
This is a toy hash-linked ledger with a real SHA256 calculation and a small mining puzzle. It does not demonstrate distributed consensus, adversarial security, finality, or a production cryptocurrency.
Edit, compare, recompute
- 1Change Data in block 1. Compare its Hash with block 2's Prev. The link updates automatically; it is not a stale reference.
- 2Read the local test. A valid block's hash starts with
0000. A changed hash usually fails this puzzle, though it can meet the prefix by chance. - 3Mine from left to right. Mine searches for a nonce for one block, then updates downstream hashes. Continue through later invalid blocks; mining block 1 does not mine the rest.
Recovery and limits
Keep your edited data and re-mine to rebuild the local sequence. Reload restores this page's initial fields and discards all unsaved edits here. The row scrolls horizontally to reach blocks 2–5.
The nonce search is capped at 500000; completion alone is not proof of success. Check the Hash prefix. If none is found, change the payload and try again. Recomputing every block shows that this local history can be rewritten: valid puzzle labels do not establish consensus or security.