BlockDAG by Hand

A hash is a fingerprint. Chain the fingerprints and you get a blockchain — which must throw away every block mined in parallel. Kaspa keeps them all instead, and GHOSTDAG puts them in order.

Work through the six tabs and the whole thing is built out of parts you can poke. The last three share one DAG: build it under BlockDAG, and GHOSTDAG re-colours it while Ordering re-sequences it.

Hash Block Blockchain BlockDAG GHOSTDAG Ordering

Data Kaspa mines a block every second.

SHA-256

Mined

Block

Nonce

Data

Hash

Mine

Add block on tips Add block on selection Undo Reset example

Click blocks to select parents, then add a block on that selection. Blocks with no children yet are tips.

k =

4

Reset example

Blue — well connected Red — outside the cluster Selected parent chain n = blue score

k =

4

Reset example

Click a block to edit the transaction it carries. Format: Alice -> Bob: 20

What to try

1. Hash — add a space at the end of the data. Everything changes; the length never does.
2. Block — type anything, watch it go red, then mine it.
3. Blockchain — edit block 2 and re-mine it. Everything after it stays broken until re-mined in turn.
4. BlockDAG — select an old block and build on it. That is a lagging miner, and the DAG absorbs the work instead of discarding it.
5. GHOSTDAG — drag k to 0 to get Bitcoin’s rule, then back up to 6.
6. Ordering — select tip H on the BlockDAG tab, add two blocks, and watch the double spend flip from Bob to Carol.

Each tab has a page that explains it properly, starting at what Kaspa is.

Simplified for teaching

SHA-256 stands in for BLAKE3 and kHeavyHash, difficulty is fixed at four leading zeros, and selected-parent ties are broken by block label rather than by hash. The GHOSTDAG implementation itself is faithful: selected parent by blue score, the two-sided k-cluster check, a virtual block over the tips, and mergesets sorted topologically with blue priority.