# Gas Optimization Tips

By [KevinWang](https://paragraph.com/@kevin-wang) · 2025-08-30

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In Ethereum, the execution of contract will cost gas fee. An excellent contract should cost gas fee as low as possible.

In this article, I will summary some gas optimization tips.

1 Storage Optimization
======================

In Ethereum, storage data is written in contract account, which will cost the most gas fee.

1.1 Reduce writing storage data
-------------------------------

We can use memory to storage middle data, instead of always writing storage data.

    uint256 a = storageVar;  // read storage
    a += 10;                  // memory operation
    storageVar = a;           // write storage
    

1.2 Merge Variable
------------------

Solidity aligns storage slots on 32-byte boundaries, multiple uint8 or bool values can be packed into the same slot.

    struct Packed {
        uint128 a;
        uint128 b;
    }
    

1.3 Use memory instead of Storage
---------------------------------

Use memory instead of Storage except the storage variable is necessary.

2 For-each Optimization
=======================

Use mapping instead of for-each searching array.

Mapping does not occupy continuous storage space, and read/write operations are relatively inexpensive.

3 Function call Optimization
============================

3.1 Short circuit
-----------------

If there are other judgment conditions before function call, we can prioritize judgment of prerequisite conditions.

    if (a > 10 && expensiveCheck()) { ... }
    

3.2 Function modifier
---------------------

`External` is cheaper than `Public`.

`Pure` and `View` not cost gas fee.

4 Data type Optimization
========================

Use minimum sufficient data type. Like `uint8`, `uint16` are more storage space-efficient than `uint256`.

5 Event Optimization
====================

5.1 Index
---------

Use as little as possible indexed parameter.

Index will cost more gas fee.

5.2 Emit
--------

Avoid frequent `emit` large events

6 Contract Structure Optimization
=================================

6.1 Use contract library
------------------------

6.2 Inheritance chain flattening
--------------------------------

Multi-level inheritance will increase deployment Gas.

7 Bytes And Array
=================

7.1 Bytes is more efficient than string
---------------------------------------

7.2 Swap And Pop
----------------

Use swap-and-pop instead of dynamic deletion.

But this way will disorder the sequence.

    function remove(uint index) public {
        arr[index] = arr[arr.length - 1];
        arr.pop();
    }
    

8 Unchecked
===========

Using `unchecked` to skip overflow checking can save gas fee.

    unchecked { i++; }

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*Originally published on [KevinWang](https://paragraph.com/@kevin-wang/gas-optimization-tips)*