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Spec-driven development

Define what you’re building before you build it

Most software projects fail for the same reason: teams start coding before they understand what they’re building. They assume requirements are obvious. They skip the hard questions. They discover gaps halfway through development when fixing them costs ten times more.

Spec-driven development flips this pattern. Instead of code being the source of truth, the specification becomes the source of truth. We define exactly what needs to be built across four domains before writing a single line of code.

The result: you build the right thing the first time.

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What is spec-driven development

Spec-driven development treats specifications as living, executable artifacts rather than static documents that get ignored after the kickoff meeting.

The core idea is simple: intent before implementation.

Traditional development starts with a vague idea and figures out requirements as it goes. Problems surface mid build. Scope creeps. Timelines slip. Budgets explode.

Spec-driven development starts with comprehensive specification. Every angle gets examined. Every assumption gets validated. Every requirement gets documented. Only then does building begin.

The philosophy

We adapted our approach from the open source spec-kit methodology, modified to work with our 4 domain validation framework. The key principles:

  1. Specification is the source of truth
    Not the code. Not the design. Not someone’s memory of what was discussed. The specification document defines what gets built.
  2. Intent over implementation
    We focus on what needs to happen and why before worrying about how to build it. Technology choices come after requirements are clear.
  3. Iterative clarification
    Specifications aren’t written once and forgotten. We iterate through questions until no gaps remain. Every ambiguity gets resolved before coding starts.
  4. Comprehensive domain coverage
    We examine the product idea through four distinct lenses: business, design, functional, and technical. Each domain surfaces different types of requirements.

The 4 validation domains

Every prototype idea gets examined through four domains. Each domain asks different questions and surfaces different requirements. Together, they create comprehensive coverage that prevents building the wrong thing.

Domain 1: business and project context

What this domain covers:
  • Why you’re building this and what problem it solves
  • Who it’s for and what success looks like
  • Timeline, budget, and resource constraints
  • Priorities and trade-offs (must-haves vs nice-to-haves)
  • Risks, assumptions, and dependencies
  • Competitive positioning and market context

Why it matters: Without business context, you might build something technically impressive that nobody needs. This domain ensures the prototype validates what actually matters to your business.

What gets surfaced: Business model implications, revenue expectations, success metrics, market positioning, strategic alignment.

Domain 2: design, brand, and content

What this domain covers:
  • How it looks (visual design, colors, typography, layout)
  • How it moves (animations, transitions, interactions)
  • How it sounds (voice, tone, brand personality)
  • What it says (content, messaging, writing style)
  • How design gets built and delivered

Why it matters: Design isn’t decoration. It’s how users experience your product. This domain ensures the prototype reflects your brand and creates the right user experience.

What gets surfaced: Brand guidelines, visual direction, content requirements, interface patterns, accessibility needs.

Domain 3: functional requirements and user flow

What this domain covers:
  • What users can do (features, actions, capabilities)
  • How users do it (flows, steps, interactions)
  • Who can do what (roles, permissions, access control)
  • How users move through the product (journeys, navigation)
  • How users are guided (onboarding, help, error handling)

Why it matters: Features sound simple until you map out exactly how they work. This domain turns vague feature requests into specific, buildable requirements.

What gets surfaced: User roles, permission structures, workflow sequences, interaction patterns, edge cases.

Domain 4: technical aspects and architecture

What this domain covers:
  • How to build it (languages, frameworks, architecture)
  • Where it runs (infrastructure, hosting, deployment)
  • How systems connect (APIs, integrations, third-party services)
  • How data is managed (databases, storage, backups)
  • How it stays secure (authentication, encryption, compliance)
  • How it performs (speed, scalability, reliability)

Why it matters: Technical decisions made early affect everything that follows. This domain ensures we choose the right technology for your specific situation.

What gets surfaced: Platform decisions, integration requirements, data structures, security needs, performance expectations.

Why four domains?

A product idea touches all four areas. Skip any one and you’ll have gaps:

  • Skip business: You build something nobody needs
  • Skip design: Users can’t figure out how to use it
  • Skip functional: Features don’t work as expected
  • Skip technical: The architecture can’t support what you’re trying to do

By examining every idea through all four lenses, we catch problems that single domain approaches miss.

How the process works

Spec-driven development isn’t a one time document. It’s an iterative process that continues until everything is clear.

Step 1
Generate Questions

We take your product idea and run it through all four domains. This generates a comprehensive set of questions that need answers. Some questions are obvious. Others you've never considered. That's the point.

Step 2
Answer and Clarify

You answer the questions. Some answers are straightforward. Others require discussion or research. As you answer, new questions often surface. An answer in the Business domain might raise questions in the Technical domain. An answer about user roles might reveal workflow gaps.

Step 3
Iterate Until Clear

We repeat this cycle: answer questions, surface new questions, answer those, surface more. The process continues until no questions remain. Every requirement is documented. Every assumption is validated. Every ambiguity is resolved.

Step 4
Create The Plan

Once everything is clear, we create the implementation plan. This defines exactly what gets built, in what order, using what technology. The specification becomes the single source of truth that guides the entire build.

How long this takes

Timeline varies by complexity:

  • Simple prototype: 2-4 hours of specification work
  • Medium complexity: 1-2 days
  • Complex product: 3-5 days

The investment pays off immediately. Every hour spent on specification saves multiple hours of rework later.

Why this catches what others miss

The “users” example

Here’s a real scenario that illustrates why comprehensive specification matters.

A client comes to us and says: “I need a system with users.”

Simple, right? Everyone knows what users are.

But when we run this through our domain checklists, questions emerge:

From business domain:
  • How many users? Dozens or thousands?
  • Are they paying customers or internal staff?
  • What’s the user growth expectation?
From functional domain:
  • How do users log in? Email and password? Social login? Single sign-on?
  • Do you need different roles? Admin, manager, regular user, guest?
  • What can each role do? View only? Edit? Delete? Approve?
  • Can users belong to multiple organizations?
  • Who assigns roles? How?
From technical domain:
  • Do you need to integrate with existing identity systems?
  • What authentication security level? Two factor?
  • How long do sessions last?
  • What happens when a user is deactivated?

Suddenly, “I need a system with users” isn’t simple at all.
The client realizes they have choices:

  • Simple user profiles with email login (3-4 hours to build)
  • Full role based access control with permissions (30-40 hours to build)

Without these questions, the client might assume simple, the developer might build complex, and both end up frustrated.

With these questions, the client makes an informed decision about what they actually need. The specification captures that decision. Everyone builds the right thing.

What traditional approaches miss

Freelancer kickoff calls cover the basics but miss the nuances. They ask “what do you want?” but not “what happens when two users try to edit the same record?”

Agency discovery phases often focus on business requirements and skip technical implications. They document features but not how features interact.

Low-code platforms let you build fast but can’t ask domain crossing questions. They don’t surface the interaction between business rules and technical constraints.

Our 4 domain approach catches the nuances because it systematically examines every angle. The checklist ensures nothing gets skipped.

What you get

At the end of spec-driven development, you receive a single comprehensive document that defines exactly what gets built.

The product specification

What it contains:
Business context
  • Problem being solved and why it matters
  • Target users and their characteristics
  • Success metrics and how they’ll be measured
  • Priorities and trade-offs (what’s essential vs optional)
  • Constraints and dependencies
Design direction
  • Visual principles and brand alignment
  • Content requirements and messaging
  • User experience guidelines
  • Interface patterns and standards
Functional requirements
  • User roles and permissions
  • Feature specifications with acceptance criteria
  • User flows and interaction patterns
  • Edge cases and error handling
Technical architecture
  • Platform and framework decisions with rationale
  • Data structure and relationships
  • Integration requirements
  • Security and performance expectations

How to use it

During build: The specification guides every development decision. When questions arise, the spec has the answer.

During validation: When testing the prototype with users, you compare their experience against what the spec defined. Did we build what we specified?

Moving to production: The specification carries forward. You’ve already validated requirements, so production development starts from a solid foundation.

Team alignment: Share the specification with stakeholders, developers, designers. Everyone sees the same documented truth instead of making different assumptions.

Frequently asked questions

Traditional discovery focuses on understanding what you want. Spec-driven development focuses on defining exactly what gets built.

Discovery might produce a requirements document. Spec-driven development produces an executable specification that directly guides implementation.

The difference: discovery outputs go into a folder. Specification outputs drive the build.

We strongly advise against it. Here’s why:

Specification typically costs 10-15% of total project budget. But skipping it causes 80% of common project failures: scope creep, wrong assumptions, missing requirements, costly rework.

Every hour spent on specification saves 3-5 hours of development time. Every question answered early is a problem avoided later.

For extremely simple projects (single feature, obvious implementation), we streamline specification. But we never skip it entirely.

You might be surprised. Clients often think they know exactly what they want until the domain questions start.

“I want users” becomes a choice between simple profiles and complex role management. “I need a dashboard” becomes decisions about real time updates vs cached data. “It should be fast” becomes specific performance targets and architectural trade-offs.

Even when you know what you want, specification ensures everyone agrees on the details. It surfaces the implicit assumptions that cause problems later.

Detailed enough to build from. Not detailed enough to waste time.

We focus on requirements and constraints, not exhaustive documentation for its own sake. The goal is clarity: does everyone understand what gets built and why?

For simple prototypes, specification might be a few pages. For complex products, it might be a comprehensive document with multiple sections.

The depth matches the complexity.

Sometimes. Specification is thorough but not perfect. During build, we occasionally discover gaps or better approaches.

When this happens:

  • We flag the issue immediately
  • We discuss options with you
  • We agree on the path forward
  • We update the specification

 

Small adjustments happen automatically. Significant changes require discussion and may affect timeline or budget.

The specification evolves, but it remains the source of truth.

Spec-driven development is Step 1 of our prototyping process:

  1. Spec-Driven Development (this page) – Define what we’re building
  2. AI-Assisted Build – Build the prototype fast
  3. Validate and Decide – Test with users, choose next steps

The specification from Step 1 guides everything in Steps 2 and 3. Without it, the build would be guesswork.

See the complete prototyping process

It carries forward to production.

If the prototype validates and you move to full development, the specification becomes the foundation for production planning. Requirements are already documented. Decisions are already made. Scope is already defined.

You’ve done the hard work of clarifying what to build. That work doesn’t get repeated.

Ready to define what you’re building?

Spec-driven development prevents the expensive mistake of building the wrong thing. Let’s examine your idea through all four domains and create a specification that guides the build.

See pricing and get started

Questions about how specification works for your specific project? Contact us and we’ll walk through the process.

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