The 9 Common Mistakes to Avoid in Custom Development

What are the most common mistakes in custom development? Among the most frequent are poorly defined requirements, a lack of feature prioritization, postponing complex tasks/features until the end of the project, insufficient automated testing, and failing to involve end users. These mistakes can slow a project, increase costs, and harm the quality of the delivered product.

In this article, we present 9 common mistakes to avoid in custom development, with concrete examples and practical recommendations to help you succeed in your projects.

The most costly mistake: not clearly defining project requirements

The first mistake to avoid in custom development is neglecting to clearly define needs and requirements. This step is crucial, as it lays the foundation for the entire project. If it is ignored or rushed, your software may become much more expensive to develop.

With vague or poorly defined requirements, the development team can misinterpret your needs and steer the project in the wrong direction. The result: some parts of the application sometimes need to be completely rebuilt, causing delays and budget overruns.

The house analogy illustrates this well: you wouldn’t build a home without plans. Likewise, in software development it is essential to create a solid plan before starting to code. Without it, the “foundation” of your application might be inadequate and fail to meet your real needs.

Finally, keep in mind that it is much less costly to revise a requirements specification or mockups than to modify code during the development phase. Investing time in the requirements definition phase will save you efficiency, quality, and cost later on.

Not involving end users during design and quality assurance phases

One of the major mistakes in custom software development is neglecting end-user participation. After the analysis phase, it’s recommended to create interactive visual mockups and have them validated directly by the people who will use the product daily. For example, in the pharmaceutical field, involving pharmacists, specialists, or even members of the public when applicable helps identify necessary adjustments early and avoids inconsistencies in the user experience.

Involvement should not stop at design. End users should also participate in quality assurance phases to test the product under real conditions before deployment. Their feedback can sometimes translate into suggestions for new features, which can be noted and added to a backlog. However, their comments can also highlight concrete issues related to interfaces or usability that must be corrected quickly.

A concrete example was our touchscreen project for Lion Electric, validated from the start by bus drivers to ensure accessibility and user-friendliness of the interfaces. This upstream collaboration allowed us to deliver a product perfectly adapted to users’ needs.

Not regularly presenting project progress to the client

Another common mistake in custom development is failing to regularly present progress to stakeholders. These people are often the primary users of the product and contributed to defining the requirements. Not sharing the project’s evolution can lead to misunderstandings or unpleasant surprises at the end.

The Scrum Guide specifies that a sprint should last no longer than one month, but it can often be shorter. At Exolnet, the best practice is therefore to split the project into two-week sprints and hold a demo at the end of each sprint. These demonstrations quickly reveal issues, help adjust priorities, and validate that the solution is evolving in the right direction.

It is important to remember that demos do not need to be perfect. Even if a feature is not fully finished, showing it is beneficial to gather feedback and detect potential problems as early as possible.

In short, transparency and continuous communication with your stakeholders reduce risk, improve collaboration, and ensure a project aligned with your real needs.

Failing to properly prioritize features and always including “nice-to-haves”

Another common mistake in custom development is poor feature prioritization. Without a clear hierarchy, it’s easy to weigh down the project with secondary elements that slow delivery and increase initial costs.

The best practice is to classify each feature by importance: essential, desirable, or optional (“nice-to-have”). For larger projects, a numeric prioritization scale (for example 1 to 5) can also be used. This method helps teams make informed decisions in the event of unforeseen issues.

Here is a table illustrating a simple feature prioritization

For a concrete example: an official launch is scheduled for a fixed date, but some features are taking longer to develop than expected. With clear prioritization, the team can lower the priority of certain secondary items to ensure delivery of a viable, functional product on time.

In short, proper feature prioritization enables faster delivery, cost control, and ensures the software first meets users’ essential needs.

Postponing complex or risky features until the end

In custom development, it can be tempting to start with simpler features to show quick visible results. Yet this approach increases risk.

Software engineering best practices recommend prioritizing the most complex or riskiest features. A study published on Science Direct highlights the importance of identifying and mitigating risks during the early sprints rather than postponing them.

By addressing them at the project’s start, the team eliminates major uncertainties and avoids finding themselves at the last minute with critical tasks that cannot be deferred. Moreover, these features often require senior resources who are in high demand. Engaging them early ensures better planning and optimal use of their expertise.

Releasing a large phase all at once instead of in small steps

Releasing a piece of software in a single big phase is like building a house and asking the occupants to move in without checking whether the plumbing works, the electricity is connected, or the foundations are solid. If a problem is discovered at that stage, fixes become much more complex and costly.

By choosing a gradual rollout, you validate each step as you go, similar to building a house with inspections at each major phase. This approach confirms that choices are correct, involves users in the process, and enables quick adjustments.

Result: fewer risks, better final quality, and a motivated team thanks to achieving clear, measurable milestones.

Neglecting code coverage and automated testing

Building a custom application without giving importance to code coverage and automated testing is a common mistake. These tests do not replace manual testing, but they complement it effectively. Without them, every new feature forces the team to retest the entire application, which is time-consuming, costly, and unrealistic as the project grows.

Integrating automated tests, on the other hand, allows regressions to be detected automatically, secures changes, and maintains a high level of quality throughout development. They also provide greater confidence during deployments, as each change is validated by this safety net.

At Exolnet, we recommend a code coverage of at least 80%, a threshold that significantly reduces the risk of regressions and ensures long-term product stability. Discover all our projects that follow this good code coverage practice.

Not clearly defining a “Definition of Done”

A common mistake in custom development is working without a clear “Definition of Done.” This concept consists of establishing precise criteria to determine when a task or feature is truly complete. Without these criteria, interpretation is left open, which can lead to misunderstandings, incomplete tasks being considered finished, and ultimately project delays.

A well-defined “Definition of Done” serves as a common guide for the development team and QA analysts. It ensures each deliverable meets the same quality standards before being considered complete. It also makes tracking project progress easier and prevents delivering a partially functional product.

Here is an example of a “Definition of Done” used at Exolnet:

• The feature meets the expected use cases

• The feature is proofread and free of errors (e.g., Antidote)

• The integrated feature matches the mockups

• The feature has been tested on supported resolutions (from 360 to 1920 pixels)

• The feature has been tested on Chrome macOS, Edge Windows, and a mobile device (Android or iPhone)

• The feature has been manually tested (main scenario, alternative scenarios, and critical cases)

• I have self-reviewed my own code (refactored and commented as needed)

• Changes are accompanied by tests proving that the code works

• Changes do not generate new warnings (e.g., Chrome console)

• Changes do not break the build

• Documentation has been updated accordingly (README, architecture documents, etc.)

Not establishing standards or documentation

Custom software can have a lifespan of ten years or more if well maintained. To ensure its longevity, it’s essential to define clear coding standards and keep documentation up to date. Without these elements, any team change introduces knowledge loss risk and lengthens the learning curve.

Documentation plays a key role in facilitating onboarding of new resources and ensuring continuity in the product’s evolution. Without reference points, the team risks spending time understanding existing functionality instead of improving the software. The quality level is also likely to degrade over time.

Ideally, implementing an internal Wiki that consolidates the project’s essential information is a good practice. Comparable to a mini Wikipedia dedicated to the product, it centralizes technical guides, architectural decisions, and development best practices.

The 9 mistakes to avoid in custom development

To succeed in a custom development project, it is essential to avoid certain common pitfalls. Here’s a summary of the 9 major mistakes to keep in mind:

• Not clearly defining project requirements: a poorly defined foundation leads to delays and extra costs.

• Not involving end users: their feedback is essential to validate the design and the real experience.

• Not regularly presenting progress: transparency prevents surprises and enables quick adjustments.

• Poor feature prioritization: distinguishing essentials from optionals ensures a viable product on time.

• Waiting until the end to develop complex features: managing risks earlier secures the project and better mobilizes senior resources.

• Releasing a large phase all at once: favour progressive deliveries to test and adjust step by step.

• Neglecting automated tests and code coverage: a technical safety net prevents and reduces costly regressions.

• Working without a “Definition of Done”: clear criteria prevent delivering incomplete tasks.

• Forgetting to define standards and documentation: these are essential to ensure continuity and ease onboarding of new resources.

Conclusion

The common mistakes to avoid in custom development highlight how much the success of a software project depends on solid foundations. A clear definition of requirements from the start prevents delays and overruns. Involving end users ensures an experience better suited to their needs, while transparency with stakeholders and feature prioritization make it easier to deliver a viable product on time. On the technical side, addressing complex tasks early, progressing in stages, and integrating automated tests significantly reduce risks. Finally, establishing clear completion criteria and maintaining standards with solid documentation ensure the software’s stability and continuity over time.

Have a project in mind? Contact us today to discuss it with our team.

FAQ

What is the most costly mistake in custom development?

The most costly mistake is poorly defining needs and features. If a requirement is misunderstood or poorly documented, a feature sometimes needs to be rebuilt, leading to major delays and cost overruns. To avoid this, it’s essential to write a comprehensive requirements specification validated by all stakeholders.

To make an analogy, it’s like building a house without a plan: it may not meet your expectations and you’ll likely have to rebuild or correct certain parts.

How do you avoid an incomplete requirements specification?

The best way is to work with a business analyst or a product owner. These experts ensure your needs are well documented and prioritized. A complete requirements specification typically ranges from 20 to 100 pages and takes several weeks to prepare. If yours is only a few pages, it is probably incomplete.

How do you avoid choosing the wrong software development team?

You should evaluate a development team based on several criteria: technical expertise, company culture, working methodology, preferred technologies, and post-deployment support. For an informed choice, compare at least 2 or 3 proposals based on common criteria.