MetaMask, Transactions and Sepolia

Setting up the wallet (MetaMask)Search on YouTubeBookmarkSaved

MetaMask is a browser-extension (and mobile) wallet for Ethereum and other chains. It holds your keys, shows balances and signs transactions. The deck walks through setup with screenshots:

1. Go to metamask.io and click Get MetaMask.
2. Choose Browser Extension and your browser (Chrome, Firefox, Brave; the deck uses Microsoft Edge with the Chrome Web Store).
3. Click Get, then Add extension. Edge warns the extension can read and change data on all websites, display notifications, and modify copied and pasted data.
4. Choose Create a new wallet (the other option is "I have an existing wallet").
5. Pick Use Secret Recovery Phrase (instead of Continue with Google, Apple or Telegram).
6. Create a MetaMask password (at least 8 characters). Tick "If I lose this password, MetaMask can't reset it". The password unlocks MetaMask on this device only.
7. Save your Secret Recovery Phrase: tap to reveal the 12 words, write them down in order, keep them safe. Make sure no one is watching your screen.
8. Confirm your Secret Recovery Phrase by filling the missing words in the right order. MetaMask shows "Perfect. Never share this phrase with anyone, ever."
9. On "Help improve MetaMask", untick "Gather basic usage data" and "Product updates" if you want, then Continue.
10. "Your wallet is ready!": click Open wallet. Pin the extension to the toolbar.

The wallet opens on Account 1 with an address like 0xc32BB...4A2B7. The home screen shows "Fund your wallet", buttons Buy, Swap, Send, Receive, and tabs Tokens, Perps, DeFi, NFTs, Activity.

Enabling test networksSearch on YouTubeBookmarkSaved

1. Open the menu (three lines). You can also choose Open full screen.
2. Go to Networks (Manage networks).
3. Turn on Show test networks. Sepolia, Linea Sepolia, MegaETH Testnet and Monad Testnet appear.
4. In the network selector, choose Sepolia under Testnets.

Block explorer (Etherscan)Search on YouTubeBookmarkSaved

A block explorer is a website that shows blocks, transactions and addresses of a chain. etherscan.io is the Ethereum mainnet explorer. Its home page shows ETH price, market cap, transaction count, gas price, last finalised block, latest blocks and latest transactions.

Search your wallet address. A new address shows ETH balance 0, no transactions sent, and "There are no matching entries".

For the testnet use https://sepolia.etherscan.io/.

Making your first transactionSearch on YouTubeBookmarkSaved

Two types of testnetsSearch on YouTubeBookmarkSaved

Getting Sepolia ETH from a faucetSearch on YouTubeBookmarkSaved

A faucet gives free test ETH. The lab uses the Google Cloud Web3 faucet:

https://cloud.google.com/application/web3/faucet/ethereum/sepolia

1. Select network Ethereum Sepolia.
2. Paste the wallet address (the "Ironman" account in the deck).
3. Click Get 0.05 Sepolia ETH. The tokens are queued, then "Transaction complete! Check your wallet address" shows the recipient and transaction hash.
4. Check the wallet: with Sepolia selected, it shows 0.0500 SepoliaETH.
5. Check the address on sepolia.etherscan.io: balance 0.05 ETH and one incoming transaction.

Sending ETH between accountsSearch on YouTubeBookmarkSaved

The deck sends 0.01 SepoliaETH from account "Ironman" to account "Spiderman":

1. Click Send, choose the recipient, enter 0.01.
2. The review screen shows From, To and Network (Sepolia). It also shows Network fee (about 0.0001 SepoliaETH), Speed (Market, about 12 sec), Max fee and Nonce 0 (the sender's first transaction).
3. Confirm. Spiderman's wallet now shows 0.0100 SepoliaETH.
4. On Etherscan, Ironman's address lists two transactions: the faucet deposit (IN) and the transfer (OUT).

Gas feeSearch on YouTubeBookmarkSaved

Open the transaction on Etherscan. The deck highlights these fields:

$\text{Transaction fee} = \text{gas used} \times \text{effective gas price}$

Interacting with the Sepolia testnetSearch on YouTubeBookmarkSaved

Prerequisites: a MetaMask wallet, funds from a faucet, one transaction between accounts, and that transaction viewed on Etherscan.

How an application talks to a public chainSearch on YouTubeBookmarkSaved

Your application (with a wallet address field and an "Explore" button) cannot talk to the Ethereum Sepolia network directly. It sends an HTTP request (or a WebSocket message) to an RPC infrastructure provider. The provider runs nodes on the network.

Your application ──HTTP POST (JSON-RPC request)──▶ Alchemy node (RPC) ──▶ Sepolia public testnet
 (PowerShell:
  Invoke-RestMethod / Invoke-WebRequest)

Getting a Sepolia RPC URLSearch on YouTubeBookmarkSaved

Get one free from Alchemy:

1. Sign in at alchemy.com.
2. Create an app (the deck's is "Jaiganesh's First App").
3. Open Endpoints. Under Ethereum, copy the Ethereum Sepolia HTTPS URL, of the form https://eth-sepolia.g.alchemy.com/v2/<API_KEY>.
4. App Settings has Rotate API key if the key leaks. The old key stops working shortly after rotation.

JSON-RPC methods usedSearch on YouTubeBookmarkSaved

1. Network / blockchain information

2. Account information

3. Transaction information

• eth_getTransactionByHash returns the sender, receiver, value, gas, nonce, transaction data and block information.
• eth_getTransactionReceipt tells whether the transaction was successfully included. It gives status, gas used, block number and transaction logs.

4. Sending transactions: eth_sendRawTransaction.

JSON-RPC structureSearch on YouTubeBookmarkSaved

{"jsonrpc":"2.0","method":"SOME_METHOD_NAME","params":[...],"id":1}

The deck works directly in PowerShell to understand the logic. Invoke-RestMethod sends HTTP/HTTPS requests to REST APIs and parses the JSON response into PowerShell objects.

Network queriesSearch on YouTubeBookmarkSaved

eth_chainIdSearch on YouTubeBookmarkSaved

$RPC_URL="YOUR_SEPOLIA_RPC_URL"

$body = '{"jsonrpc":"2.0","method":"eth_chainId","params":[],"id":1}'

Invoke-RestMethod `
    -Uri $RPC_URL `
    -Method Post `
    -ContentType "application/json" `
    -Body $body

Result: 0xaa36a7. In decimal that is 11155111, the Sepolia chain ID.

The same call with curl on Linux:

curl -s -X POST "$RPC_URL" -H "Content-Type: application/json" \
     -d '{"jsonrpc":"2.0","method":"eth_chainId","params":[],"id":1}'

eth_blockNumberSearch on YouTubeBookmarkSaved

$body = '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":2}'

Result 0xb13404. Convert hex to decimal in PowerShell:

[Convert]::ToInt64("B13404", 16)     # 11613188

eth_getBlockByNumberSearch on YouTubeBookmarkSaved

$body = '{"jsonrpc":"2.0","method":"eth_getBlockByNumber","params":["0xb13404",false],"id":4}'

The second parameter: false returns only transaction hashes, true returns full transaction objects. By default Invoke-RestMethod truncates long JSON output. Expand it:

$body = '{"jsonrpc":"2.0","method":"eth_getBlockByNumber","params":["0xb13404",true],"id":4}'
$response = Invoke-RestMethod -Uri $RPC_URL -Method Post -ContentType "application/json" -Body $body
$response | ConvertTo-Json -Depth 5

The block shows hash, parentHash, sha3Uncles, miner, stateRoot, transactionsRoot, receiptsRoot, logsBloom, difficulty (0x0 after the move to Proof of Stake), number, gasLimit, gasUsed and timestamp.

eth_getBlockByHashSearch on YouTubeBookmarkSaved

$BLOCK_HASH="0x...4db87e"
$body = "{`"jsonrpc`":`"2.0`",`"method`":`"eth_getBlockByHash`",`"params`":[`"$BLOCK_HASH`",false],`"id`":5}"

The body is in double quotes so $BLOCK_HASH expands. Inner quotes are escaped with a backtick.

eth_gasPriceSearch on YouTubeBookmarkSaved

$body = '{"jsonrpc":"2.0","method":"eth_gasPrice","params":[],"id":6}'

Result 0x3ea60403. The value is in Wei. 1 ETH = 1,000,000,000,000,000,000 Wei ($10^{18}$).

eth_getBlockTransactionCountByNumberSearch on YouTubeBookmarkSaved

$body = '{"jsonrpc":"2.0","method":"eth_getBlockTransactionCountByNumber","params":["0xb12F70"],"id":7}'

Result 0x61 = 97 transactions in block 11612016. Etherscan shows the same "97 transactions" for that block.

Account queriesSearch on YouTubeBookmarkSaved

eth_getBalanceSearch on YouTubeBookmarkSaved

$ADDRESS="0x...2B7"
$body = '{"jsonrpc":"2.0","method":"eth_getBalance","params":["' + $ADDRESS + '","latest"],"id":8}'
$result = Invoke-RestMethod -Uri $RPC_URL -Method Post -ContentType "application/json" -Body $body
$result

"latest" is the block tag: the balance at the newest block. Result 0x8deb4b5219eda0 Wei. Make it readable:

Write-Host "Address: $ADDRESS"
Write-Host "Balance (Wei): $($result.result)"
$balanceWei = [System.Numerics.BigInteger]::Parse(
    $result.result.Substring(2),
    [System.Globalization.NumberStyles]::AllowHexSpecifier
)
Write-Host "Balance (ETH): $([double]$balanceWei / 1e18)"

Substring(2) strips the 0x. Divide by 1e18 to get ETH. MetaMask shows 0.0399 SepoliaETH.

eth_getTransactionCountSearch on YouTubeBookmarkSaved

$body = '{"jsonrpc":"2.0","method":"eth_getTransactionCount","params":["' + $ADDRESS + '","latest"],"id":9}'

Result 0x1: Ironman has sent one transaction, so its next nonce is 1. Received transactions do not count.

eth_getCodeSearch on YouTubeBookmarkSaved

$body = '{"jsonrpc":"2.0","method":"eth_getCode","params":["' + $ADDRESS + '","latest"],"id":10}'

Result 0x. 0x means no contract bytecode exists at that address.

eth_getStorageAtSearch on YouTubeBookmarkSaved

Needs a deployed smart contract, so the deck leaves it for later. Reference snippet:

$CONTRACT="0xYOUR_CONTRACT_ADDRESS"
$SLOT="0x0"
$body = '{"jsonrpc":"2.0","method":"eth_getStorageAt","params":["' + $CONTRACT + '","' + $SLOT + '","latest"],"id":11}'
$result = Invoke-RestMethod -Uri $RPC_URL -Method Post -ContentType "application/json" -Body $body
$result

Transaction queriesSearch on YouTubeBookmarkSaved

eth_getTransactionByHashSearch on YouTubeBookmarkSaved

The Ironman to Spiderman transaction:

$TX_HASH="0x50e5f5f7f696bbe1eabf95cd5c903a226ff7f4857840a4d69a19a62755da79a3"
$body = '{"jsonrpc":"2.0","method":"eth_getTransactionByHash","params":["' + $TX_HASH + '"],"id":12}'
$result = Invoke-RestMethod -Uri $RPC_URL -Method Post -ContentType "application/json" -Body $body
$result

Result fields (hex) include: type 0x2, chainId 0xaa36a7 (11155111), nonce 0x0, gas 0x7b0c (31500), maxFeePerGas 0xb1034988 (2969782664 Wei), maxPriorityFeePerGas 0x59682f00, to, value 0x2386f26fc10000 (0.01 ETH). Then come accessList, input 0x, signature r, s, yParity, v, hash, blockHash, blockNumber 0xb12f70, transactionIndex 0x3, from, gasPrice.

Invoke-WebRequest returns the raw response instead of parsed objects:

$response = Invoke-WebRequest -Uri $RPC_URL -Method Post -ContentType "application/json" -Body $body
$response.Content

PowerShell shows "Security Warning: Script Execution Risk" because it parses the page. Answer Y, or add -UseBasicParsing. Pretty-print with an online JSON parser, or:

$response.Content | ConvertFrom-Json | ConvertTo-Json -Depth 10

eth_getTransactionReceiptSearch on YouTubeBookmarkSaved

Gives the execution result (receipt) after the transaction is included in a block.

$body = '{"jsonrpc":"2.0","method":"eth_getTransactionReceipt","params":["' + $TX_HASH + '"],"id":13}'
$response = Invoke-WebRequest -Uri $RPC_URL -Method Post -ContentType "application/json" -Body $body
$response.Content | ConvertFrom-Json | ConvertTo-Json -Depth 10

In the lab: type 0x2, status 0x1, gasUsed 0x5208 (21000), contractAddress null.

Reference: "JSON-RPC API" on ethereum.org.

Quick self-testSearch on YouTubeBookmarkSaved