Read Contract vs Write Contract

In the era of decentralized finance (DeFi) and blockchain-based applications, interacting directly with smart contracts through block explorers like Etherscan has become an essential skill. However, according to observations from the team of experts at Tan Phat Digital, the fundamental difference between the two main interaction methods — "Read Contract" and "Write Contract" — is often misunderstood, leading to confusion about costs, execution speed, and especially the safety of digital assets. The following analysis will delve into the technical architecture of the Ethereum Virtual Machine (EVM), token standards, and vulnerabilities that users frequently encounter.

Architectural Principle: Separation Between Mutable State and Data Query

The foundation of the distinction between read and write operations lies in the way the Ethereum network stores data. State variables in Solidity are permanently stored on the blockchain and are part of the network state maintained by all nodes. Accessing or modifying these variables requires different execution mechanisms in EVM.

Read Operations

Read operations, represented by the "Read Contract" tab on Etherscan, are the process of querying information that has been encrypted or stored in the contract without changing the state of the blockchain. Technically, these functions are often defined with modifiers like view or pure. A view function allows reading state variables or balances but commits not to modify them, while a pure function is even more restrictive in that it neither reads nor writes to state, only performing calculations based on input parameters.

The key point that often confuses users is the "free" nature of these operations. When a user queries the balance or token name via Etherscan, the browser makes a call (call) to an Ethereum node via the RPC protocol (eth_call). Since this operation does not change the overall state of the network, it does not require global consensus and therefore does not cost gas. However, a subtle misunderstanding arises when these read functions are called by another write function on-chain; in that context, they still consume gas as part of the overall transaction.

Write Operations

In contrast, the "Write Contract" tab represents actions that change the state of the blockchain, such as transferring funds, updating ownership, or approving permission to spend tokens. Every state change must be permanently recorded on the ledger, which requires the user to actually submit a transaction (transaction). This transaction requires a digital signature from the user's wallet (like MetaMask) to prove control over the sending address.

The cost and time differences are clear: write operations consume gas — a measure of computational cost — and must wait for miners or validators to pack it into a block. Users often make mistakes when not predicting fluctuations in gas prices, leading to transactions being stuck or failing due to inappropriate gas limit settings.

Comparative Characteristics Analysis Between Read and Write Contract

1. Read Contract (Call) operation:

Main purpose: Query current data from blockchain.
Solidity modifier: Use keyword view or pure.
Gas Fee (Off-chain): Completely free when making queries from browser browse.
Wallet signature required: No signature required from personal wallet.
Network impact: Only happens locally at node-level.
Response time: Response is almost instantaneous.
Possibility of failure: Very low, usually only due to logic errors in the source code.

2. Write Contract (Transaction) operation:

Main purpose: Change state or data on the blockchain.
Solidity modifier: No limit keyword (or use payable).
Gas Fees: Always require Gas fees to be paid in the network's base currency.
Wallet Signature Required: Signature required to authenticate ownership.
Network Impact: Global Impact via consensus mechanism.
Response Time: Depends on speed network performance and gas prices.
Possibility of failure: High, possibly due to gas shortage, wrong nonce, authority error or contract logic.

See more: What is Blockchain Explorer?

Analyzing Common Mistakes in Write Contract Operations

When interacting directly with the "Write Contract" interface on Etherscan, users often bypass the protection layer of regular dApp interfaces, leading to to having to directly face strict technical requirements.

Decimals Precision Mistakes

This is the most common technical risk causing direct financial loss that Tan Phat Digital wants to warn about. In Solidity, integers (uint256) are preferred because the network does not support floating point numbers. Therefore, every token has a decimals parameter.

Users often mistakenly believe that every token uses the standard 18 decimal digits similar to ETH. However, in reality there is a big difference:

Ethereum (ETH): 18 decimals. The raw value for 1 unit is 1 x 10^{18} (Wei).
Wrapped Bitcoin (WBTC): 8 decimals. The raw value for 1 unit is 1 x 10^8 (Satoshi).
Tether (USDT): 6 decimals. The raw value for 1 unit is 1 x 10^6.
USD Coin (USDC): 6 decimals. The raw value for 1 unit is 1 x 10^6.
DAI Stablecoin: 18 decimals. The raw value for 1 unit is 1 x 10^{18}.
Shiba Inu (SHIB): 18 decimals. The raw value for 1 unit is 1 x 10^{18}.

For example: If you want to transfer 1,000 USDC, you must enter 1000000000. If you only enter 1000, the actual amount transferred is only 0.001 USDC.

Calculation Error: Division Before Multiplication and Rounding

In smart contracts, performing division before multiplication is a classic mistake. Because uint256 always rounds down, if an intermediate calculation returns a result less than 1, it becomes 0 immediately. Users when providing parameters to "Write" functions need to pay attention to the order to avoid triggering these logical error conditions.

See more: Transaction ID (TxID) is What?

Approval Ecosystem and Security Pitfalls

The "Approve" mechanism allows third parties to spend tokens on behalf of users, but this is also a weakness that is often exploited.

The Infinite Approval Myth

Most dApps require "infinite" approvals to save gas for times later. Users often copy the maximum value of uint256 without understanding that they are giving full control over the balance to that contract. If the contract is hacked, the attacker can empty your wallet without any further confirmation.

Confusion Between Disconnect and Revoke

Many Web3 users believe that "Disconnect" wallets are safe, but they are not:

1. Disconnect Wallet:

Placement: Operation on the dApp interface or wallet widget.
Gas Fee: Completely free.
Impact: Only hide the wallet address from the website interface. The smart contract retains previously approved withdrawal rights.
Purpose: Secure personal privacy.

2. Revoke Approval:

Purpose: Absolute asset security.

Proxy Architecture and Transaction Errors

Projects often use the "Proxy Contract" model to upgrade source code. Confusion between Proxy address and Implementation address often leads to errors. Users need to use the "Is this a proxy?" on Etherscan to properly interact with the "Read as Proxy" or "Write as Proxy" tabs.

Decoding Errors When Executing Write Contract

Out of Gas Error: Occurs when the gas limit you set is lower than necessary. All gas fees paid will be lost and the transaction will fail. Never default to 21,000 gas for complex contract interactions.
Execution Reverted Error: Gas is sufficient but the contract logic is stopped due to wrong authorization, insufficient balance, or violation of the require condition. Increasing gas will not resolve this error.
Nonce Error: Each transaction has a sequence number (nonce). If a low-fee transaction gets stuck, subsequent transactions with larger nonces will also get stuck, causing wallet congestion.

Indexing Data and Explorer Latency

Etherscan has an Indexing Lag ranging from a few seconds to a few minutes. Users often panic when the wallet reports success but Etherscan has not yet displayed new data, leading to repeated sending of wasteful transactions.

Besides, data classification is also confusing:

Transactions Tab: Displays calls directly from personal wallets, with unique hash codes (Tx Hash).
Internal Transactions Tab: Shows the ETH movement performed by contract logic. There is no separate Tx Hash but depends on the original transaction.
Token Transfers Tab: Shows the transfer of ERC-20, 721, 1155 standards based on events emitted from the contract.

15 Frequently Asked Questions (FAQs)

Why can I read the wallet balance above Etherscan without fees?
The Read operation does not change the blockchain state. Etherscan only queries data from a local node and displays it to you, so there is no need for gas or wallet signatures.
What is the difference between the "view" and "pure" functions in the Read Contract tab?
Both are gas-free when called from off-chain. However, the view function can read data from state variables in the contract, while pure neither reads nor writes, it only performs calculations based on the input.
Why does transferring 100 USDT in the Write Contract tab only show 0.0001 USDT in the wallet? Due to decimals error. USDT only has 6 decimals. If you enter "100", the system interprets it as $100 / 10^6$. To transfer 100 USDT, you must enter 100000000.
How is "Out of Gas" different from "Execution Reverted"?
"Out of Gas" is because you set the gas limit too low, miners do not have enough energy to run the code completely. "Reverted" is because the gas is enough but the contract logic actively stops the transaction because a certain condition is not satisfied (for example: wrong password or insufficient wallet).
I have Disconnected the wallet from the dApp, can hackers withdraw my funds again?
Yes. Disconnect just interrupts the display interface. The "Approve" rights you signed remain valid forever on the blockchain until you perform a "Revoke" operation.
Why does Etherscan display "This contract may be a proxy contract"?
Because this contract uses a Proxy model to be upgradeable. All implementation logic resides in another contract (Implementation). You need to verify the Proxy to be able to use the "Read/Write as Proxy" tab.
How dangerous is Infinite Approval?
It allows that contract to withdraw your entire token balance at any time. If the project is hacked or the project owner has bad intentions, they can empty your wallet without you being able to stop it.
How to revoke old approval rights on Etherscan?
Go to the "Token Approval Checker" section on Etherscan, connect your wallet and press the "Revoke" button for each contract you no longer trust. This operation will cost some gas fees.
My transaction is reported successful on MetaMask but Etherscan still shows the old balance?
This is the phenomenon of indexing lag. The data on the chain has updated, but Etherscan's server system needs a few seconds to a few minutes to synchronize and display the new data.
What is an "Internal Transaction" and why doesn't it have its own hash (Tx Hash)?
These are transactions that arise from logic inside the contract (for example, the contract automatically sends you ETH). They are included in the original transaction (Normal Transaction) so there is no independent hash code.
Will I lose money if I transfer tokens to the contract address using the "transfer" function? Most likely. Some contracts do not have the functionality to handle directly deposited tokens and they will be stuck there forever. Normally you should use the "deposit" function or the official dApp interface.
Why do I need to "Wrap" ETH into WETH to trade?
Because ETH is the native currency, not following the ERC-20 standard. To interact with features like "Approve" or "TransferFrom" in DEXs, ETH must be wrapped into WETH to become a standard token.
What is Address Poisoning?
A fraudster sends a microscopic amount of money (dust) from an address whose first and last characters are identical to the address you usually use. The purpose is for you to mistakenly copy their address from the transaction history in the next transfer.
ERC-2612 Is "Permit" safer than traditional "Approve"? "Permit" helps save gas because of off-chain signing, but it carries the risk of signature phishing. Hackers can trick you into signing a message that looks harmless but actually grants permission to withdraw money.
How many Wei is 1 ETH?
In Smart Contract programming, the smallest unit is Wei. 1 ETH = 10^{18} Wei (1,000,000,000,000,000,000 Wei). Always keep this number in mind when entering values manually in the Write Contract tab.

Understanding the difference between Read and Write Contract is the strongest shield protecting you in the Web3 world. Tan Phat Digital recommends that users:

Always check the decimals of each type of token.
Prioritize limited approvals and periodically perform "Revoke".
Use Proxy testing tools to ensure sending commands to the correct address.
Calmly decode errors instead of increasing gas blindly.
Only interact with contracts that have been publicly verified (Verified).

Web3 brings financial autonomy but also requires corresponding personal responsibility. Hopefully the sharing from Tan Phat Digital will help you interact more safely and effectively on blockchain.