Consistent Naming with Voldemort Rules

How to ensure that some names just don't appear in your codebase?


Jan 05, 2023

We don't speak his name

Why Would You Avoid a Name?

In Harry Potter witches and wizards are too afraid to speak Voldemort's name - instead they call him "You-Know-Who" or "He Who Must Not Be Named".

Assuming that there aren't words you and your teammates don't dare to utter: What are reasons to avoid a name in your codebase?

This post won't come up with a deny-list of generally bad names. Rather, it will show some patterns and situations where a name is unclear or misleading in that specific context.

It's easy to underestimate the importance of names. Usually, changing names won't change the code's behavior, so why bother? Well, it turns out that names greatly influence how well humans can understand a code. As Adam Tornhill (software engineer, psychologist, and the founder of CodeScene) puts it in Software Design X-Rays:

We use the same mental processes to understand code as those we use in everyday life beyond our keyboards (evolution wasn’t kind enough to equip our brains with a coding center).

That ease of understanding in turn influences crucial metrics of a software project: How long does it take to fix a critical bug? How long does it take to add a new feature? How probable is that adding a new feature will introduce a bug?

In our survey last year, "inconsistent or confusing terminology" was mentioned as the main source of technical debt. More than 55% of the respondents regarded this as an issue in their codebase.

Technology Changes

As the code evolves, some names can become out-of-sync with the current architecture. Let's say your first implementation used the command pattern, but later, you changed it. Now, it makes sense to ensure that there are no remainders of the old implementations, like variable names with a "command" suffix or execute functions.

Business Changes

Let's say your company started out as "Great Groceries". After some years, it expanded and got renamed to "Super Store". Now (or at least soon after the big push), it makes sense to reflect this change in the codebase as well. The longer you wait with this, the bigger the confusion. And the bigger the chance that some new team members have no idea that the company was once called "Great Groceries".

This exercise is more difficult if the old brand name exists in various ways: For example, sometimes it's GreatGroceries spelled out, sometimes it's just a gg_ prefix. See also the section about synonyms.

There are several business changes that make a renaming necessary:

  • renaming a whole company
  • renaming a product that has been on the market for a while
  • replacing a code name during development with an official name

In all these cases, it makes sense to ensure that your codebase keeps up with the changes.


Synonyms make human languages more vivid. In code, however, they only cause confusion. Why do we have an object called holiday_policy and a property vacation_days_left? Do "holiday" and "vacation" refer to the same concept? 🤔 If not what's the difference and where is it documented?

In Domain-Driven Design, the very first recommendation after the introductory chapter is to create a "ubiquitous language". Communication gets much smoother if you ensure that the same terminology is used throughout the project. This includes code, documentation, but also emails and meetings.

Often, it's difficult to tell whether one name or another is a more suitable choice. But it's clear that consistency is valuable.


Some examples of synonyms where you might decide to keep only one of them:

  • yearly vs annual
  • initial vs starting vs original
  • previous vs former vs earlier


A special case is abbreviations.

Again, the recurring theme: There's no general rule when you should use an abbreviation. But consistency matters. If one field is called ordered_pieces, don't call the other one delivered_pcs.

Mysterious Names

The book Refactoring in 1999 introduced the concept of "code smells". One change in the 2018 edition of the book: A new smell "mysterious name" was added and it appears as the very first element of the list.

It's difficult to provide a general example. But if a name keeps popping up in the codebase and you keep asking yourself what it means, it might be worth creating a Voldemort rule for it.

Overly General Names

Sometimes, suffixes are attached to a name without really enhancing its meaning. Sometimes, the reason is that the class does several loosely related things and should be probably split up.

Some candidates for such too general names:

  • manager
  • util
  • coordinator

Again, this is very context-dependent. If you have a sophisticated system of Manager and Coordinator classes with clear responsibilities, leave them as they are. But if that's not the case, this rule might spot some god classes.

Names That Are Easy to Confuse

This is a tricky one. Some names are completely fine per se, but they are easy to mix up with another concept in the codebase.

Some tips:

  • Consider both the spelling and the pronunciation. The two words should be easy to distinguish both in writing and in speech.
  • Consider this especially when you're using derivations of the same root word.

An example from our own Sourcery codebase is Proposer and Proposal. Using derivations of the same root word has a big advantage: It communicates that those concepts are closely related. A disadvantage is that they look similar and they sound even more similar. During a discussion where both proposers and proposals are mentioned multiple times, it's easy to lose the thread.


To create a rule avoiding a name, you can use the Sourcery Rules Generator.

You can install it with:

pip install sourcery-rules-generator

To create "voldemort" naming rules, run the command:

sourcery-rules voldemort create

screenshot sourcery-rules voldemort create

Enter the name that should be avoided. For example: annual

You'll be prompted to provide:

  • the name that you want to avoid


5 rules will be generated:

  • function names
  • function arguments
  • class names
  • variable declarations
  • variable assignments
  - id: no-annual-function-name
    description: Don't use the name annual
    pattern: "\ndef ${function_name}(...):\n  ...\n"
    condition: function_name.contains("annual")
      - naming
      - no-annual
  - id: no-annual-function-arg
    description: Don't use the name annual
    pattern: "\ndef ...(...,${arg_name}: ${type?} = ${default_value?},...):\n  ...\n"
    condition: arg_name.contains("annual")
      - naming
      - no-annual
  - id: no-annual-class-name
    description: Don't use the name annual
    pattern: "\nclass ${class_name}(...):\n  ...\n"
    condition: class_name.contains("annual")
      - naming
      - no-annual
  - id: no-annual-property
    description: Don't use the name annual
    pattern: '${var}: ${type}'
    condition: var.contains("annual")
      - naming
      - no-annual
  - id: no-annual-variable
    description: Don't use the name annual
    pattern: ${var} = ${value}
    condition: var.contains("annual")
      - naming
      - no-annual

Let's see some situations where creating such a Voldemort rule might be a good idea.


Good names make it much easier to read and understand a codebase. Regarding that code gets read much more often than it's written, it's worth investing some effort into clear and consistent naming. This doesn't just include coming up with good names when you add a feature. It's also essential to keep the names up-to-date with the various business and technology changes.

Do you have some more examples? We are curious to hear your stories with awesome and horrible names.

Reach out at or on Twitter @SourceryAI. Join the Sourcery Discord Community.


  • 📖 Evans, Eric: Domain-Driven Design: Tackling Complexity in the Heart of Software August 2003, Addison-Wesley Professional
  • 📖 Fowler, Martin: Refactoring 2nd edition, 2018 November, Addison-Wesley Professional
  • 📖 Rowling, J. K.: Harry Potter and the Philosopher's Stone June 1997, Bloomsbury Publishing
  • 📖 Tornhill, Adam: Software Design X-Rays March 2018, Pragmatic Bookshelf