Ethereum Transaction LabMetaMask, Remix and a SimpleStorage contract on Sepolia

Wallet

Not connected

Looking for MetaMask in this browser…

Smart contract

Not set

Deploy SimpleStorage.sol from Remix IDE (opens in a new tab) with MetaMask on Sepolia, then paste the contract address and deployment transaction hash that Remix shows.

Number stored on the blockchain

—

Connect a deployed SimpleStorage contract to see its value.

Update the number

Calling store(n) changes blockchain state, so it is a transaction: you sign it in MetaMask and pay a small gas fee in SepoliaETH.

Any whole number from 0 up to 2²⁵⁶ − 1.

Connect MetaMask to send a transaction.

Transaction lifecycle

  1. Prepare (upcoming)Encode store(n) and estimate gas
  2. Sign (upcoming)Approve in MetaMask with your private key
  3. Broadcast (upcoming)Sent to the network, hash created
  4. Include (upcoming)A validator puts it in a block
  5. Confirm (upcoming)3 blocks deep in the chain

Send a transaction to watch it move through each stage of its life.

Transaction details

No transaction yet. Update the number above, or look up any Sepolia transaction hash below, such as the deployment from Remix.

How Ethereum handles this

The page above uses one tiny contract to show the two ways a program talks to Ethereum: reading data, which is free and instant, and changing data, which needs a signed, paid transaction that the whole network agrees on.

Read-only calls compared with state-changing transactions
PropertyRead-only callState-changing transaction
Example hereretrieve()store(n)
Changes the blockchainNoYes, updates contract storage
Needs a MetaMask signatureNoYes, signed with your private key
Gas feeFree for the callerPaid in ETH (SepoliaETH here)
Who runs itOne node answers locallyEvery node re-executes it
ResultReturned immediatelyTransaction hash, then a receipt
Recorded on chainNo tracePermanently, in a block
Public address and private key
Your address (0x…) is public, like an account number: anyone can send to it or look it up on Etherscan. The private key is the secret that produces signatures proving you approved a transaction. MetaMask keeps it encrypted on your device. Anyone with your private key or recovery phrase controls the account, so never share either one.
Gas and gas fees
Gas measures the computation and storage a transaction uses. Writing a number to storage costs far more gas than a plain ETH transfer (21,000 gas). Fee = gas used × gas price, where the price is a base fee that is burned plus a priority tip for the validator. Fees stop spam and infinite loops and reward the network for doing the work.
Validators
Since 2022 Ethereum uses proof of stake. Validators lock up 32 ETH, take turns proposing a block every 12 seconds, re-execute each transaction to check it, and attest that blocks are valid. Dishonest validators lose part of their stake. They play the role miners had under proof of work.
Transaction hashes
The hash is a unique 32-byte fingerprint (Keccak-256) of the signed transaction. MetaMask returns it the moment the transaction is broadcast, before it is mined, so you can track it on a block explorer. Changing any detail of a transaction would give it a completely different hash.
Blocks and confirmations
A transaction is included once a validator puts it in a block and a receipt shows its status and gas used. Each later block adds a confirmation. More confirmations mean it is harder to reverse; after about two epochs (roughly 13 minutes) the block is finalized.