sandbox · no real money · nothing to install
Blockchain simulator
Every idea from the session as a little machine you can push buttons on. Pick any card — they are all open — press the buttons, and watch the picture react.
send coins to another player
waiting for another player to join this room… open this page in a second tab or share the link with the class.
- no transfers yet — be the first to pay a classmate.
14 simulations · start anywhere
- 1 servermany nodesslide 2 · fundamentalsDecentralization
Kill nodes in a central server vs a peer network and see who survives.
Knock out the central serverKnock out nodes in the peer networkopen simulation → - honest#1#2#3#4#5✓attacker#1#2orphaned ✕slide 3 · consensusDouble spending
Attack the chain with a conflicting spend and see confirmations defeat it.
Pay the merchantLaunch the conflicting spendopen simulation → - database · updateold value gonebalance = 40ledger · appendhistory kept+100−60+0slide 4 · fundamentalsBlockchain vs conventional database
Run the same UPDATE and DELETE on both and compare what is left behind.
Run UPDATE on both sidesRun DELETE on both sidesopen simulation → - →block 10000a…→block 20001a…→block 30002a…block 40003a…slide 6 · fundamentalsImmutability
Tamper with a block and watch every hash after it break — then try to re-mine.
Edit the text inside a blockWatch every later hash breakopen simulation → - BTC · 7 tpsETH · 15 tpsL2 · 2k tpsVisa · 24k tpsslide 10 · fundamentalsPerformance & scalability
Throughput, latency and finality across Bitcoin, Ethereum, L2s and Visa.
Drag the congestion sliderCompare tps, fees and finalityopen simulation → - youmempoolblockthemslide 13 · fundamentalsBTC & ETH transfers
Send simulated coins: BTC spends UTXOs on mempool.space, ETH updates an account on Etherscan.
Pick BTC or ETH and set a feeSend and follow each stageopen simulation → - PoWPoSDPoSPBFTslide 16 · consensusConsensus algorithms
Run a round of PoW, PoS, DPoS and PBFT side by side and compare trade-offs.
Run a round of each algorithmCompare speed, cost and trustopen simulation → - →wallet · confirm1.25 ETH0xa41f…9c2bslide 19 · ethereumMetaMask transaction
A replica wallet flow: connect, review gas, confirm, sign, and get a receipt.
Connect the fake walletReview the gas screenopen simulation → - pragma soliditycontract Counter {uint256 public n;function inc()6080604052348015610010f3560e01cbytecodeslide 21 · contractsSolidity syntax & coding
Walk a contract line by line: pragma, state, visibility, modifiers, events.
Step through the contract line by lineRead what each keyword doesopen simulation → - call inc()contractstoragen = 1slide 22 · contractsSmart contracts
Deploy a contract, call its functions, and watch storage and events change.
Deploy the contractCall its functionsopen simulation → - oracle→condition→keeper→payoutslide 23 · contractsSmart contract automation
An escrow that releases itself — conditions, triggers, keepers and oracles.
Fund the escrowLet the oracle reportopen simulation → - naive88k gaspacked31k gasslide 24 · contractsAdvanced contract writing
Gas costs, storage vs memory, mappings, inheritance and custom errors.
Toggle the gas optimisationsCompare gas before and afteropen simulation → - proxydelegatecall →storage keptlogic V1logic V2slide 27 · contractsProxy contract approach
Upgrade logic from V1 to V2 through delegatecall while storage survives.
Call V1 through the proxyUpgrade to V2open simulation → - attacker↺ withdraw()↺ withdraw()↺ withdraw()vaultslide 28 · securitySmart contract vulnerabilities
Exploit re-entrancy, overflow/underflow and 'private' data — then patch them.
Run the exploitRead what the attacker didopen simulation →