Deciphr Academy
Track 2 · Keeping crypto safe · Module 11

Reading the chain

Use a block explorer to check any wallet, token or transaction yourself.

Lessons
7
Reading
50 min
Quiz
15 questions
Pass mark
80%
  1. 1What a block explorer isWhat is a block explorer, and what can it do?6 min
  2. 2Reading a transaction pageHow do you read a transaction on a block explorer?8 min
  3. 3Token transfers and logsWhy does a token payment show 0 ETH on a block explorer?8 min
  4. 4Checking a walletHow do you check a crypto wallet on a block explorer?7 min
  5. 5Checking a token or contractHow do you check whether a token is the real one?7 min
  6. 6Bitcoin is differentHow do you read a Bitcoin transaction on a block explorer?7 min
  7. 7Verifying a payment: the Brindlecove caseHow do you check that a crypto payment someone says they sent really arrived?7 min

The case used in this module

Each module tells its own made-up Brindlecove story, so details can differ from one module to the next.

Key words

Block explorer
A website that searches a blockchain's public records and shows transactions, addresses, blocks and tokens in readable form. It can't change the chain.12
Transaction hash
A unique code for one transaction, used to look it up. Also called a transaction ID or txid.34
Block confirmation
A count of how far a transaction is buried. Each new block on top adds one. More confirmations make a transaction safer to rely on.35
Gas used
The exact units of gas a transaction used. An explorer multiplies it by the gas price to show the fee.3
Effective gas price
The price actually paid per unit of gas: the base fee plus the tip.6
Input data
Extra data sent with a transaction, most often the function call for a smart contract.7
Method ID
The first 4 bytes of the input data. They pick which contract function to run. Also called the function selector.89
Event log
A record a smart contract writes while it runs, for apps outside the chain to read. Explorers show logs on a Logs tab.10
Transfer event
The log an ERC-20 token contract must write whenever tokens move. It holds from, to and value.11
Internal transaction
ETH moved by a smart contract as part of a transaction someone else started.1213
Decimals
A token setting that says where the decimal point goes. Divide the raw number by 10 to the power of decimals to get the amount people see.1411
Public name tag
A name an explorer shows next to an address. It comes from the explorer, not from the chain.15
Verified contract
A contract whose source code an explorer has checked compiles to the code on the chain. It does not mean the contract is safe.1617
Token approval
Permission you give an app to spend your tokens. Explorers can list approvals and help you revoke them.1819
UTXO
An unspent transaction output: an amount of bitcoin waiting to be spent by a later input.4
Change output
An output that sends the leftover of a Bitcoin payment back to the sender.20
Sources
  1. What is a Block Explorer?. Etherscan Information Center, 9 April 2026, updated 4 August 2026.
  2. How to refund a Transaction?. Etherscan Information Center, 27 November 2019, updated 21 June 2026.
  3. What is a Transaction Hash (Txn hash)?. Etherscan Information Center, 5 December 2019, updated 21 June 2026.
  4. Transactions (Bitcoin Developer Guide). Bitcoin Developer Documentation (developer.bitcoin.org).
  5. Payment Processing: Verifying Payment (Bitcoin Developer Guide). Bitcoin Developer Documentation (developer.bitcoin.org).
  6. JSON-RPC API. ethereum.org developer docs, page updated 28 June 2026.
  7. Understanding Transaction Input Data. Etherscan Information Center, 2 May 2023, updated 21 June 2026.
  8. Method ID. Etherscan Information Center, 25 September 2023, updated 21 June 2026.
  9. Transactions. ethereum.org developer docs, page updated 7 October 2026.
  10. Event Logs. Etherscan Information Center, 21 September 2023, updated 22 September 2026.
  11. ERC-20: Token Standard. Ethereum Improvement Proposals (Fabian Vogelsteller, Vitalik Buterin), created 19 November 2015, status Final.
  12. Understanding an Ethereum Transaction. Etherscan Information Center, 24 August 2020, updated 21 June 2026.
  13. User FAQs. Blockscout documentation.
  14. ERC-20. OpenZeppelin Contracts 5.x documentation.
  15. Public Name Tags, Labels & Public Notes. Etherscan Information Center, 7 February 2021, updated 21 June 2026.
  16. Verifying smart contracts. ethereum.org developer docs, page updated 22 October 2025.
  17. Explore a Contract Address on Etherscan. Etherscan Information Center, 11 March 2020, updated 21 June 2026.
  18. Explore an EOA Address on Etherscan. Etherscan Information Center, 31 December 2019, updated 21 June 2026.
  19. How to revoke smart contract access to your crypto funds. ethereum.org guide, page updated 6 June 2026.
  20. Mastering Bitcoin, 3rd edition, chapter 2: How Bitcoin Works. Andreas M. Antonopoulos and David A. Harding (CC BY-SA 4.0), GitHub, December 2023.