10 Different Types of Software Bugs

No software has ever been created perfectly on the first try. As mistakes are a natural aspect of any development process, software testers tend to encounter bugs, errors, and other defects each day, although some much more often than others. Thankfully, many of these mistakes can be noticed fairly easily when it comes to software development.

However, the type of error can significantly vary, from the more insignificant and harmless ones that don’t present a serious threat, to those that could become much more problematic, causing your software to crash, or even lose important data.

For this reason, it’s vital to get familiar with all the different forms of software errors and bugs that exist, as well as their level of severity, and their implications.

What exactly are software bugs?

Software bugs represent any flaws or errors that can be found in a program, application, or system, causing the product to create an undesirable or even entirely incorrect result. A large percentage of bugs stem from the mistakes that were unintentionally made when designing software or its source code, or even from the components and the OS that were used.

While smaller bugs might be a common occurrence that can easily be fixed, software can also have more serious defects that tend to cause effects on a larger scale, such as freezing, crashing, or even security risks.

That is why it’s important to pinpoint and fix any potential issues (a process known as debugging) in an effort to produce safer and more reliable software. However, you might need to learn more about the different forms of bugs and errors that exist in order to achieve this.

The most common types of software bugs

Once you’ve familiarized yourself with the definition of a software bug, it is now time to get to know all the different types of errors that exist, allowing you to pinpoint any software issues more easily. To that end, here are some of the most common software bug types:

1. Crashing

In case a program, operating system, or other software solution no longer works properly, it automatically causes itself to shut down, thus leading to a crash. While this tends to be the result of a software error more often than not, crashes can also be caused by hardware devices, leading to even more issues and damage.

Although they’re among the most common issues that occur, crashes can also be some of the more dangerous errors a developer could face. In case the relevant software data wasn’t properly protected or backed up, significant losses might be suffered after a crash, due to the lack of time and option to save any changes.

2. Syntactic errors

These types of errors represent any improperly spelled words or grammatically incoherent phrases that can clearly be noticed during testing. Due to human nature, syntactic errors occur quite commonly, especially when it comes to aspects such as translation, but might be a bit more difficult to spot, for this same reason.

When testing the GUI of the software, it’s vital to shift between languages and inspect the correlation of elements to any relevant documentation. Thankfully, the potential syntactic errors that are found are just as easily fixed.

3. Calculation errors

Calculations are a crucial aspect of nearly all software processes, ensuring elements properly add up, and everything works smoothly. However, errors in calculation can still occur, mostly due to coding and algorithm errors, data mismatch, incorrect logic or formulas, etc.

While this generally tends to be a minor issue, incorrect calculations have been known to result in quite high costs through history, such as causing accidents or losing money. For this reason, it is essential for all calculations to be thoroughly examined.

4. Communication errors

These issues tend to occur during the communication between the software and the end-user. All software should be simple to use while providing all the necessary information that users have to know on the screen. In case these criteria aren’t met, communication issues occur.

Some examples of this error are misnamed buttons that perform unexpected actions, the lack of a Help menu, and undocumented features and updates. Although these issues might not seem so significant at first, they will often lead users to opt for competitive software that’s more user-friendly.

5. Functional errors

Functionality represents the manner in which the software is expected to behave. If an aspect of the software seems confusing, difficult to manage, or even impossible to perform, that means that there is a functional error present.

As all software tends to have a wide array of functions, these types of errors can vary as well, from smaller issues such as unclickable tabs to bigger problems like being unable to utilize the main function of the software at all. But even though functional errors occur quite often, they are also simple to notice during the testing.

6. Missing command errors

As the name suggests, this issue arises when an expected command is missing from the software. Considering the fact that all programs can have a wide variety of commands as well, this particular error can also range from smaller issues like the absence of a needed button to bigger problems such as no logical option.

In more practical terms, the missing command error occurs when a user doesn’t have the option to perform an action or activity that’s commonly expected. This happens when there’s no ‘X’ button to close a pop-up window, or when you can’t cancel an order in an online store, for instance.

7. Control flow errors

The control flow of any form of software represents the actions that will happen next, as well as the conditions under which they will occur. In case there are any unexpected issues within this flow, such as wrong actions or no actions at all, the control flow error occurs, which might significantly impact the functionality of the entire software.

For instance, if a user is filling out a form on one page, and then clicks on the ‘Save and Continue’ button, they will expect the form to be saved, and to be redirected to the next page. In case they stay on the same page, this would be a control flow error.

8. Boundary related errors

Everything in the world has its own, specific limit, and the same is true for software resources. Whether it’s memory and text size limits or even the limited number of users, all software will have some boundaries that aren’t recommended to cross. In case these boundaries aren’t taken into account during the development process, they might cause functionality issues down the road.

While boundary related errors tend to be quite a rare occurrence, history has seen some notorious examples of this issue that ended up being an incredibly costly and time-consuming mistake, such as the famous “Millennium bug”.

9. Error handling errors

Any problems that arise during the user interaction with the software should be operated clearly and successfully. The end-user should be informed about the issue as best as possible and offered a potential solution. When this doesn’t happen it’s known as an error handling error.

An example of this issue would be a user getting a pop-up message only saying ‘Error’ or ‘Try Again’, with just the ‘OK’ button available. Instead, the user should be provided with an explanation of what the error was (missing a field, inability to save) as well as steps to resolve the problem (required actions, validation messages).

10. Hardware usage error

Whenever software is used on an incompatible device or environment, it’s known as a hardware usage error. These types of issues are most commonly caused by the wrong OS, low-performance power, or unsupported devices.

A solution to this issue would be to adapt the software to a wider array of devices that have the performance capabilities to run it. Wherever applicable, it might also be wise to provide hardware that is best adjusted to the specific software.

Classifying bugs by severity levels

The severity level of an error represents the impact the bug in question will have on the functionality, performance, and the software overall. Bugs are generally divided into the following severity levels:

  • Low-severity errors – The issues that are mostly linked to the User Interface, and are generally considered to be minor, such as differently sized fonts and action buttons.
  • Medium-severity errors – The issues that cause smaller functions to perform in unexpected ways, like hyperlinks that don’t work, or lead to an incorrect source.
  • High-severity errors – The issues that prevent important software functions from performing properly, or cause the entire software to behave in unpredicted ways, like control flow errors and most functional errors.
  • Critical errors – The issues that block the functionality of the entire software, and usually prevent further testing, such as constant error messages or crashes.

Classifying bugs by their priority

The priority of an error represents the urgency with which the bug in question will have to be addressed, which most commonly depends on the bug’s severity level. Here is how errors tend to be classified by their priority:

  • Low-priority errors – The issues that don’t necessarily have to be addressed straight away, but should be fixed before the software release, such as syntactic errors and appearance issues with the UI.
  • Medium-priority errors – The issues that are best fixed before the final release, but aren’t particularly harmful, like minor communication errors or improper formats and adaptions to different mediums.
  • High-priority errors – The issues that need to be repaired before the final release, in an effort to meet all necessary criteria, like missing command errors and control flow errors.
  • Urgent errors – The issues that have the biggest impact and must be repaired within a day of their detection, such as crashes, major calculation errors, and notable functional errors.

Why are classifications important?

When you’re more familiar with the basic severity and priority classifications, you will be able to assign the handling of these issues to the appropriate teams, in the appropriate order, thus streamlining the entire testing process. This will result in faster development procedures and might improve the overall efficiency of the software.


Human errors and mistakes are a completely natural occurrence, which tends to arise in all aspects of our lives. Unfortunately, they become a bit more important when it comes to software development, as even a single incorrect punctuation mark has been known to impact the functionality of the entire software, even rendering it completely unusable in some cases.

For this reason, the proper identification and categorization of errors are essential aspects of the development process, necessary for the functionality of your software. Hopefully, the guide above will have allowed you to get more familiar with the different forms of software bugs that exist, as well as their importance, giving you the opportunity to create a successful and efficient end-product.