refactoring

basicwidespread

Refactoring is the internal reorganization of existing program code while ensuring the program behaves exactly the same from the outside as before.

In plain terms

Imagine rearranging your kitchen: spices go on one shelf, rarely used pots go on top, and drawers get labels. You cook the same meals as before, but you find everything faster, and guests can also orient themselves. Refactoring is the same with program code.

Over the years, programs grow patch by patch, and the code becomes harder to read. During refactoring, the developer renames, splits, merges, and simplifies, but does not add new functionality or change the operation. The goal is to make the next modification cheaper, faster, and safer.

This differs from bug fixing or development: those change what the program does, while refactoring only changes how it is written. Therefore, in the best case, the user notices nothing of it.

Coding agents now also perform refactoring: you ask them to tidy up an old code section, and they carry out transformations spanning multiple files. The result still needs to be verified.

How it works

First, a safety net is created: automatic tests that record how the program currently behaves.
The developer or coding agent identifies problematic parts: repetitive code, overly long functions, and misleading names.
It shapes things in small steps: a rename, a highlight, a split, always only one thing at a time.
Tests run after each step. If something breaks, the last tiny step is easy to undo.
In the end, the code is clearer and easier to extend (not necessarily shorter), while the program's behavior stays the same.

An everyday example

Your company's ordering system has promised a new feature for months, but developers say they must first "refactor" it. This means the old code is so tangled that order must be restored before the new feature can be added, otherwise it would cause errors elsewhere. For two weeks, nothing appears to change, but development then accelerates.

Who is affected

developerIt is part of their daily work, and they increasingly hand it to a coding agent, whose output they must then review. → Code

entrepreneur, executiveThey must allocate time and money to work with no visible outcome, but without it the software becomes increasingly expensive to develop.

employeeIf the development of the workplace system is delayed due to "refactoring," it is worth knowing that this is maintenance, not inactivity. → Work & HR

A common misconception

MythRefactoring means rewriting the entire program.

In realityRefactoring is a series of small, controlled steps on existing code without changing its functionality. A complete rewrite is a completely different, much riskier undertaking.

Limits and risks

Without testing, it is risky because nothing indicates if the program's behavior has changed unnoticed during transformation.
It brings no new feature or direct revenue, so the business side easily postpones it until the code is barely modifiable.
A coding agent can confidently perform a transformation that looks good but still breaks a rare case, so larger changes must be reviewed by a human.
A poorly designed system cannot be saved: fundamental structural flaws require a deeper redesign.

Similar, but not the same

rewrite – In rewriting, the old code is discarded and started from scratch, while refactoring improves the existing code step by step.
bug fixing – Bug fixing changes the program's faulty behavior, while refactoring intentionally leaves the behavior untouched.
optimization – The goal of optimization is faster or more efficient execution, while the goal of refactoring is code that is more understandable and easier to maintain.

Related concepts

Broader

software development, software maintenance, code quality

Narrower

renaming, function highlighting, eliminating code duplication

On the edge

technical debt, coding agent, automated testing, code verification, legacy system

A brief history

Programmers already used the term in the 1980s. William Opdyke developed it with scientific rigor in his 1992 doctoral dissertation. It became widely known through Martin Fowler's 1999 book Refactoring, which (along with its 2018 second edition) remains a foundational work on the subject.

Where things stand

Refactoring has been a standard practice in software development for decades, with development tools providing built-in support. By the end of 2026, it has become a common task for coding agents, but human oversight of major transformations remains necessary.

Status: 2026 November

Also known as

refactoring · Refactoring · code refactoring · code refactoring · code refactoring · refactoring · code refactoring · refactor

Sources

This entry was machine-edited and has undergone machine expert review; the “In the news” section updates automatically from Agent Age stories.