Design Practice

Apply the 6-phase design framework to understand a problem before implementing a solution.

Phases

Work through each phase sequentially. Do not skip phases. The goal is understanding, not artifacts.

PHASE 1: DESCRIBE (Symptoms)

Objective: Capture the reality without imposing solutions.

1. Gather signals:

   • What symptoms are observed? (errors, complaints, metrics)
   • Where do they occur? (files, components, conditions)
   • When did they start? (commits, deployments, changes)
   • Who is affected? (users, systems, processes)

2. Write a neutral description:

   • Facts only, no speculation on causes
   • No mention of solutions
   • Observable behaviors, not interpretations

Output format:

## Description

### Observed Symptoms
- [Symptom 1]: [Where/When observed]
- [Symptom 2]: [Where/When observed]

### Signal Sources
- [Bug reports, logs, user complaints, metrics]

### Timeline
- [When symptoms first appeared, any patterns]

Anti-patterns to avoid:

• "The database is slow" (diagnosis, not description)
• "We need to add caching" (solution, not description)
• "Users are confused by the UI" (interpretation, not observation)

Correct examples:

• "Page load time exceeds 5s when user count > 100"
• "Error rate increased from 0.1% to 2.3% after deploy on Jan 15"
• "Users submit support tickets asking how to find the export button"

PHASE 2: DIAGNOSE (Root Cause)

Objective: Identify the mechanism causing the symptoms.

1. Generate multiple hypotheses:

   • List at least 3 possible causes
   • "If I only have one hypothesis, I'm probably wrong"

2. Test hypotheses systematically:

   • Use logic to rule things out (negative progress)
   • Use evidence to support remaining hypotheses
   • Divide and conquer (git bisect, component isolation)

3. Write the Problem Statement:

Problem Statement Template:

## Problem Statement

**Current behavior:** [What happens now - factual]

**Mechanism:** [Root cause - how/why it happens]

**Evidence:**
- [Fact supporting this diagnosis]
- [Fact supporting this diagnosis]

**Ruled out:**
- [Hypothesis A]: [Why it's not this]
- [Hypothesis B]: [Why it's not this]

Quality check: The solution should feel obvious after writing the right problem statement. If it doesn't, the diagnosis is incomplete.

PHASE 3: DELIMIT (Scope)

Objective: Define what's in and what's out.

1. Set explicit boundaries:

   • What subset of the problem will we solve?
   • What constraints do we accept?
   • What's explicitly NOT being addressed?

2. Document non-goals:

   • Future considerations
   • Related problems not in scope
   • Nice-to-haves deferred

Output format:

## Scope

### In Scope
- [What we will address]
- [Specific constraints we'll work within]

### Out of Scope (Non-Goals)
- [What we explicitly won't do]
- [Why it's deferred]

### Constraints
- [Technical limitations]
- [Time/resource constraints]
- [Compatibility requirements]

Why this matters: Prevents scope creep. Sets the "physics" of the project before considering solutions.

PHASE 4: DIRECTION (Strategic Approach)

Objective: Select the best approach from viable alternatives.

1. Generate multiple approaches:

   • Status Quo: Always include "do nothing" as baseline
   • Approach A: [First viable approach]
   • Approach B: [Different viable approach]
   • Approach C: [If applicable]

2. Build a Decision Matrix:

Decision Matrix Structure:

## Decision Matrix

| Criterion | Status Quo | Approach A | Approach B |
|-----------|------------|------------|------------|
| [Criterion 1] | [Fact] | [Fact] | [Fact] |
| [Criterion 2] | [Fact] | [Fact] | [Fact] |
| [Criterion 3] | [Fact] | [Fact] | [Fact] |

### Criteria Definitions
- **[Criterion 1]**: [What this measures]
- **[Criterion 2]**: [What this measures]

### Assessment Key
- Green: Desirable
- Yellow: Acceptable with trade-offs
- Red: Problematic or blocking

Rules for Decision Matrix:

• Text is FACT (neutral, objective descriptions)
• Color/assessment is JUDGMENT (subjective evaluation)
• Status Quo is always the first column
• Each cell must be specific, not "good" or "bad"

3. Select and justify:

### Decision

**Selected approach:** [Approach name]

**Rationale:** [Why this approach best addresses the scoped problem]

**Trade-offs accepted:** [What we're giving up]

PHASE 5: DESIGN (Tactical Plan)

Objective: Create detailed blueprint for implementation.

Only after Direction is selected:

1. Define specifics:

   • Data structures and schemas
   • API signatures and contracts
   • Component responsibilities
   • Error handling approach
   • Edge cases

2. Write Implementation Plan:

Use the standard implementation plan format with:

• Phases that can be independently verified
• TDD approach (tests before implementation)
• Specific file paths and changes
• Success criteria for each phase

Hammock time: Write the plan, then sleep on it. Read it the next day before proceeding.

PHASE 6: DEVELOP (Execute)

Objective: Translate design into working code.

If Phases 1-5 were rigorous, this phase should feel mechanical:

• Follow the plan
• Write tests first
• Implement to pass tests
• Verify against success criteria

If you're struggling in this phase: Return to earlier phases. Struggling to code usually means the design is incomplete.

Process Rules

1. No phase skipping: Each phase builds on the previous
2. Artifacts are thinking tools: Not bureaucracy, but aids to understanding
3. Hammock time: Sleep on ideas before committing to them
4. Multiple hypotheses: One idea is a trap; generate alternatives
5. Incremental over iterative: Understand → Design → Code → Value (not Code → Fail → Learn)

When to Return to Earlier Phases

• Can't write Problem Statement clearly → Back to Describe (need more symptoms)
• Solution doesn't feel obvious → Back to Diagnose (incomplete root cause)
• Scope keeps expanding → Back to Delimit (boundaries not firm)
• Can't choose between approaches → Back to Direction (need more criteria or research)
• Implementation keeps hitting surprises → Back to Design (missing edge cases)