Contract verification on Etherscan in Blockchain / Solidity - Step-by-Step Execution

Concept Flow - Contract verification on Etherscan

Write Smart Contract Code

↓

Compile Contract to Bytecode

↓

Deploy Contract on Blockchain

↓

Get Contract Address

↓

Go to Etherscan Verification Page

↓

Submit Source Code + Compiler Settings

↓

Etherscan Compiles and Matches Bytecode

Shows the step-by-step process from writing a smart contract to verifying it on Etherscan by matching compiled bytecode.

Execution Sample

Blockchain / Solidity

pragma solidity ^0.8.0;

contract SimpleStorage {
    uint storedData;
    function set(uint x) public {
        storedData = x;
    }
}

A simple Solidity contract storing a number, ready to be compiled and deployed.

Execution Table

Step	Action	Input/Condition	Result/Output
1	Write contract code	SimpleStorage contract code	Source code ready
2	Compile contract	Solidity compiler v0.8.0	Bytecode generated
3	Deploy contract	Bytecode on blockchain	Contract address assigned
4	Open Etherscan verification page	Contract address input	Verification form loaded
5	Submit source code + compiler settings	Source code + compiler version + optimization	Etherscan compiles source
6	Compare compiled bytecode with on-chain bytecode	Bytecode match?	Yes - verification success
7	Verification result	Success	Contract source code published on Etherscan

💡 Verification stops after bytecode matches on-chain bytecode or fails if no match

Variable Tracker

Variable	Start	After Step 2	After Step 3	After Step 5	Final
source_code	SimpleStorage code	Same	Same	Submitted to Etherscan	Published on Etherscan
bytecode	None	Generated by compiler	Deployed on blockchain	Recompiled by Etherscan	Matched on-chain bytecode
contract_address	None	None	Assigned after deployment	Used for verification	Used for verification

Key Moments - 3 Insights

Why must the compiler version and optimization settings match exactly during verification?

Because Etherscan recompiles the source code with the provided settings and compares bytecode. If settings differ, bytecode won't match, causing verification to fail (see execution_table step 5 and 6).

What happens if the bytecode does not match during verification?

Verification fails and the source code is not published. This is shown in the concept_flow where 'No Match' leads to 'Verification Failed'.

Why do we need the contract address for verification?

The contract address tells Etherscan which on-chain bytecode to compare against the compiled source code (see execution_table step 4 and 6).

Visual Quiz - 3 Questions

Look at the execution_table, what is the output after step 3 (Deploy contract)?

A Contract address assigned

B Source code published

C Bytecode generated

D Verification failed

💡 Hint

Check the 'Result/Output' column for step 3 in the execution_table.

At which step does Etherscan compare the compiled bytecode with the on-chain bytecode?

A Step 4

B Step 6

C Step 5

D Step 7

💡 Hint

Look for the step mentioning 'Compare compiled bytecode' in the execution_table.

If the compiler version submitted to Etherscan is different from the one used to deploy, what will happen?

A Contract address will change

B Verification will succeed

C Verification will fail due to bytecode mismatch

D Source code will be automatically corrected

💡 Hint

Refer to key_moments about compiler version and optimization settings.

Concept Snapshot

Contract verification on Etherscan:
1. Write and compile smart contract.
2. Deploy contract to blockchain.
3. Get contract address.
4. Submit source code and compiler settings on Etherscan.
5. Etherscan recompiles and compares bytecode.
6. If matched, source code is published for transparency.

Full Transcript

Contract verification on Etherscan is the process of proving that the source code you wrote matches the code deployed on the blockchain. First, you write your smart contract code and compile it to get bytecode. Then you deploy this bytecode to the blockchain, which gives you a contract address. To verify, you go to Etherscan, enter the contract address, and submit your source code along with the exact compiler version and optimization settings you used. Etherscan recompiles your source code and compares the bytecode with the one on the blockchain. If they match, verification succeeds and your source code is published on Etherscan for anyone to see. This process helps users trust the contract by seeing its source code. If the bytecode does not match, verification fails. It is important to use the exact compiler settings to avoid mismatch. The contract address is needed so Etherscan knows which deployed code to compare against.