Contract verification on Etherscan in Blockchain / Solidity - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to specify the contract address for verification.

Blockchain / Solidity

const contractAddress = '[1]';

Drag options to blanks, or click blank then click option'

A0x1234567890abcdef1234567890abcdef12345678

BcontractABI

CetherscanAPIKey

D0xabcdef

Attempts:

3 left

💡 Hint

Common Mistakes

Using the ABI or API key instead of the contract address.

The contract address must be a full Ethereum address string to verify on Etherscan.

2fill in blank

medium

Complete the code to set the Etherscan API key for contract verification.

Blockchain / Solidity

const apiKey = '[1]';

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AYOUR_ETHERSCAN_API_KEY

BverificationStatus

C0x1234567890abcdef1234567890abcdef12345678

DcontractAddress

Attempts:

3 left

💡 Hint

Common Mistakes

Using the contract address or other variables instead of the API key.

The API key is a string provided by Etherscan to authorize verification requests.

3fill in blank

hard

Fix the error in the verification function call by completing the method name.

Blockchain / Solidity

await etherscan.[1](contractAddress, sourceCode, apiKey);

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AdeployContract

BgetContract

CcompileSource

DverifyContract

Attempts:

3 left

💡 Hint

Common Mistakes

Using unrelated method names like deployContract or compileSource.

The correct method to verify a contract on Etherscan is 'verifyContract'.

4fill in blank

hard

Fill both blanks to create a dictionary with contract address and API key for verification.

Blockchain / Solidity

const verificationData = { address: '[1]', key: '[2]' };

Drag options to blanks, or click blank then click option'

A0xabcdefabcdefabcdefabcdefabcdefabcdefabcd

BcontractABI

CYOUR_ETHERSCAN_API_KEY

DsourceCode

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up the API key and contract address values.

The 'address' field needs the contract address, and 'key' needs the Etherscan API key.

5fill in blank

hard

Fill all three blanks to complete the verification function call with address, source, and API key.

Blockchain / Solidity

await etherscan.verifyContract('[1]', '[2]', '[3]');

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AcompileSource

BsourceCode.sol

CYOUR_ETHERSCAN_API_KEY

D0xabcdefabcdefabcdefabcdefabcdefabcdefabcd

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping the order of arguments or using incorrect values.

The function requires the contract address, the source code filename, and the API key in that order.

Practice

1. What is the main purpose of verifying a smart contract on Etherscan?

easy

A. To make the contract source code public and trusted

B. To increase the gas cost of contract deployment

C. To hide the contract's source code from users

D. To automatically upgrade the contract's functionality

Solution

1. Step 1: Understand contract verification purpose

   Verification publishes the source code so users can see and trust it.

2. Step 2: Eliminate incorrect options

   Increasing gas cost, hiding code, or auto-upgrading are not related to verification.

3. Final Answer:

   To make the contract source code public and trusted -> Option A

4. Quick Check:

   Verification = public and trusted code [OK]

Hint: Verification means sharing source code publicly [OK]

Common Mistakes:

• Thinking verification hides code
• Confusing verification with contract upgrades
• Assuming verification increases deployment cost

2. Which of the following is the correct step to verify a contract on Etherscan?

easy

A. Deploy the contract twice on the blockchain

B. Send ETH to Etherscan wallet to activate verification

C. Upload the source code and match compiler version exactly

D. Encrypt the source code before uploading

Solution

1. Step 1: Identify verification process

   Verification requires uploading source code and matching compiler settings exactly.

2. Step 2: Remove incorrect options

   Sending ETH, deploying twice, or encrypting code are not part of verification.

3. Final Answer:

   Upload the source code and match compiler version exactly -> Option C

4. Quick Check:

   Upload code + match compiler = verification [OK]

Hint: Match compiler version exactly when uploading code [OK]

Common Mistakes:

• Ignoring compiler version mismatch
• Thinking payment is needed for verification
• Trying to encrypt source code before upload

3. Given the following Solidity contract and verification attempt, what will happen if the compiler version used during verification does not match the deployed contract's compiler version?

pragma solidity ^0.8.0;
contract Simple { uint public x; constructor() { x = 10; } }

medium

A. Verification will fail due to compiler version mismatch

B. Verification will succeed and show the source code

C. Contract will be redeployed automatically

D. Verification will succeed but source code will be hidden

Solution

1. Step 1: Understand compiler version role in verification

   Etherscan requires exact compiler version match to verify source code.

2. Step 2: Analyze mismatch effect

   If versions differ, verification fails because bytecode won't match source code.

3. Final Answer:

   Verification will fail due to compiler version mismatch -> Option A

4. Quick Check:

   Compiler mismatch = verification fail [OK]

Hint: Compiler version mismatch causes verification failure [OK]

Common Mistakes:

• Assuming verification ignores compiler version
• Thinking contract redeploys automatically
• Believing source code hides after verification

4. You tried verifying your contract on Etherscan but got an error saying "Bytecode does not match source code." What is the most likely cause?

medium

A. Your contract has no constructor

B. You used a different compiler version than the one used to deploy

C. You uploaded the wrong contract address

D. You forgot to pay the verification fee

Solution

1. Step 1: Understand bytecode mismatch meaning

   Bytecode mismatch means the compiled source code does not match deployed bytecode.

2. Step 2: Identify common cause

   Using a different compiler version or settings causes bytecode mismatch errors.

3. Final Answer:

   You used a different compiler version than the one used to deploy -> Option B

4. Quick Check:

   Bytecode mismatch = compiler version difference [OK]

Hint: Check compiler version if bytecode mismatch error occurs [OK]

Common Mistakes:

• Thinking payment is required for verification
• Confusing contract address with bytecode mismatch
• Assuming constructor presence affects verification

5. You have a contract deployed with optimization enabled during compilation. When verifying on Etherscan, which of the following must you do to successfully verify the contract?

hard

A. Verify using a different contract address

B. Disable optimization and upload source code with any compiler version

C. Only upload the ABI without source code

D. Upload source code with optimization enabled and match compiler version

Solution

1. Step 1: Understand optimization effect on bytecode

   Optimization changes compiled bytecode, so verification must match optimization settings.

2. Step 2: Match compiler version and optimization settings

   To verify, upload source code with exact compiler version and optimization enabled as deployed.

3. Final Answer:

   Upload source code with optimization enabled and match compiler version -> Option D

4. Quick Check:

   Match optimization + compiler version = successful verification [OK]

Hint: Match optimization settings and compiler version exactly [OK]

Common Mistakes:

• Ignoring optimization settings during verification
• Uploading only ABI without source code
• Trying to verify with wrong contract address