The Design Doc Dilemma: Finding the "Just Enough" in Your Two-Week Sprint

How a little upfront design can prevent your "go fast" agile team from actually 
going slow.

If you’ve worked on an agile team, you know the rhythm: backlog grooming, sprint planning, a two-week burst of coding, and then a review. The mantra is often "working software over comprehensive documentation." But if you’ve been in the trenches, you’ve also likely seen this scenario: 

A complex story gets pulled into a sprint. The team huddles for a quick 15-minute discussion, then everyone jumps straight to code. Two days later, PR comments reveal a fundamental misunderstanding. A week in, two engineers realize their implementations are incompatible. By the end of the sprint, the feature is "done," but it’s a Rube Goldberg machine of code—brittle, overly complex, and difficult to test.
The subsequent sprints are then plagued with bug fixes, refactoring, and rework directly caused by that initial rushed implementation.

Going fast ended up making us go agonizingly slow.

This isn't an indictment of agile; it's a misapplication of it. The key to avoiding this trap isn't to revert to weeks of Big Design Upfront (BDUF), but to intelligently apply "Just Enough" Design Upfront (JEDUF). And the most effective tool I've found for this is the humble design document.

Why Jumping Straight to Code Fails for Complex Problems

For simple CRUD tasks or well-trodden paths, a story description and a quick conversation are perfectly sufficient. The problem space is understood, and the solution is obvious. But for complex, novel, or architecturally significant work, code is a terrible medium for exploring ideas.

Why?

• Code is Final: Writing code is an act of commitment. Changing a core architecture decision after hundreds  of lines have been written is expensive.
• It Lacks Context: Code shows how something is done, but rarely explains the why-the considered alternatives, the trade-offs, and the rejected ideas.
• It's Isolating: Without a shared artifact, engineers can head down divergent paths, only discovering 
  their misalignment during a painful merge conflict.

The Antidote: The Targeted Design Doc

The solution isn't to document everything, but to recognize the stories that carry risk and complexity and treat them differently. For these, I advocate for a simple process:

1. Identify the Candidate: During sprint planning or grooming, flag a story as "complex." This is usually obvious—it involves new system integrations, significant performance requirements, novel algorithms, or has a high degree of ambiguity.
2. Time-Box the Design: The assigned engineer spends a few hours (not days!) drafting a concise design doc. This isn't a 50-page specification. It's a brief document that outlines:
   • The Problem: What are we actually solving?
   • The Proposed Solution: A high-level overview of the approach.
   • Considered Alternatives: What other paths did you consider? Why were they rejected?
   • Key Trade-offs: (e.g., "We chose faster performance over code simplicity here because of 
     requirement X.")
   • Open Questions: What are you still unsure about?
3. Review & Socialize: Share the doc with other senior engineers—often async, but sometimes in a quick 30-minute meeting. The goal isn't to achieve consensus, but to 
   stress-test the idea. Does this make sense? Are there hidden pitfalls? Is there a simpler, more elegant solution we're all missing?
4. Iterate or Implement: Based on the feedback, the design is improved, simplified, or sometimes rejected altogether in favor of a better approach. Now the team codes, with a clear, 
   vetted blueprint.

The Science: Knowing When to Use a Design Doc

The science,  is in the discernment. You don't do this for every story. That would be bureaucratic and slow. You do it for the ones where the cost of being wrong is high.

Use a design doc when the story involves:

• Cross-team or cross-service dependencies.
• New technology or patterns the team isn't familiar with.
• Significant performance or scaling concerns.
• High-risk areas of the codebase.
• Fundamental changes to the application's architecture.

For the vast majority of stories, the "design" is a whiteboard sketch or a conversation. But for the 10-20% that are truly complex, the design doc process is an accelerator, not a hindrance.

The Result: Speed, Quality, and Alignment

This approach transforms your process:

• Fewer Revisions: Catching design flaws in a doc is orders of magnitude cheaper than catching them in a PR.
• Collective Ownership: The entire team understands the why behind the solution, leading to better maintenance and fewer regressions.
• Knowledge Sharing: The document becomes a lasting artifact for future engineers wondering,
   "Why did we build it this way?"
• True Agility: You're not just moving fast; you're moving fast in the right direction. 
  You build quality in from the start, instead of trying to test or refactor it in later.

So, the next time your team faces a gnarly story, resist the urge to dive headfirst into the IDE. 
Take a breath, write a page, and get a second opinion. You’ll find that a small investment in thinking saves a huge amount of time in coding.

How does your team handle complex design? Do you have a process for "just enough" 
documentation? Share your thoughts in the comments below!