Today, many software developers rely on prompt first development, where a developer prompts the AI to “build a feature” and hope for the best. Any professional software engineer knows that approach is unreliable. In many ways, prompt first development is equivalent to rolling the dice with every new feature you add or modify because the AI may make mistakes and introduce bugs. Spec files significantly reduce that possibility.
Spec-Driven Development
Spec-driven development (SDD) is an approach to AI-driven software development where project definitions, feature designs, business rules, constraints, and acceptance criteria are documented in spec files. Basically, a “spec” file contains the design specifications for an application feature.
The reason “spec” files are necessary is because they improve the reliability of AI when doing software development. For example, suppose a feature in an application has a small set of business rules that apply to that feature. When first building out that feature, the developer may provide the AI with that small set of business rules. In the future, when the developer needs to change that feature, the developer should supply the same business rules. If that doesn’t happen, the AI is more likely to make a mistake and introduce a bug.
So, ideally, the developer puts those rules in a “spec” file. And any time the developer has a coding agent update that feature, the developer can simply supply that spec file and know that the coding agent has the same information as the coding agent that originally built the feature. Consequently, the coding agent makes fewer mistakes and introduces fewer bugs.
Think of a “spec” file as information about a feature that will need to re-explained to the AI, perhaps many times in the future. Without that spec file, any attempt to re-explain those rules, puts the developer at greater risk of leaving out a detail that could cause the AI to make a mistake and introduce a bug. Furthermore, those business rules may evolve overtime. And keeping those rules in spec files enables the coding agents to update features in a way that is consistent with the application’s design specifications.
Real-World Examples
To get started with spec-driven development, create a “specs” folder in your project where the spec markdown files will go.
- When starting a new session with AI, give the AI an idea of your project. That’s where a project definition spec file, or ProjectDefinition.md, comes in handy.
- Anytime AI needs to write code that interacts with the database, it needs to know the structure of that database. If that information is in a spec file, such as DatabaseDefinitions.md, simply refer to that spec file when prompting the AI to write that code.
- If an application has three different subscriber types and different rules apply to different subscriber types, put those rules in a spec file, such as SubscriberTypeRules.md. If the coding agent is not aware of those rules and makes significant changes to the code, it’s more likely ot make mistakes and introduce bugs.
If you’re looking for an easy and powerful spec-driven development tool, try Acceledesk’s MD Creator AI Agent. The MD Creator markdown editor can be downloaded for free. The AI Agent makes it super easy to generate precise documentation using Mermaid diagrams to do UMLs, ERDs, Dataflows, and other diagrams. It also generates LaTeX expressions powered by MathJax to express mathematics. The AI Agent significantly reduces the time it takes to do Spec-Driven Development from hours to minutes.