patterns-technical-decisions

Making Technical Decisions

Overview

Provide a complete framework for technology decisions: evaluate alternatives against consistent criteria, make informed choices, and document decisions so future maintainers understand WHY choices were made.

When to Use

• Choosing between technology options (libraries, frameworks, services)
• When constraints-and-decisions.md requires "NEEDS CLARIFICATION" resolution
• Documenting architectural decisions for the team
• When spec or plan requires technology choice justification
• Evaluating existing stack vs new dependencies
• Any decision with long-term maintenance implications

When NOT to Use

• Trivial changes - No architectural impact, obvious solution
• Decisions already documented - Existing ADR covers the scenario
• Emergency hotfixes - Document decision post-facto, don't block fix
• Pure implementation details - Internal code structure without external impact
• Reversible choices - Easily changed later without consequence

Decision Workflow

1. EVALUATE    →    2. DECIDE    →    3. DOCUMENT
   Options           Best fit          For posterity

Phase 1: Evaluate Options

For each decision point, consider 2-3 alternatives minimum.

Quick Criteria Reference:

Criterion	Key Question
Fit	Does it solve the problem fully?
Complexity	How hard to implement and maintain?
Team Familiarity	Does the team know this tech?
Ecosystem	Good docs, active community?
Scalability	Will it grow with the project?
Security	Good security posture?
Cost	Total cost of ownership?
Brownfield Alignment	Fits existing stack?

See EVALUATION-MATRIX.md for detailed criteria, scoring, and technology category comparisons.

Phase 2: Decide

Score options against weighted criteria. Document:

• Which option scores best
• Why criteria were weighted as they were
• What trade-offs are accepted

Quick Comparison Format:

Option	Pros	Cons	Alignment	Verdict
Option A	+ Fast, + Simple	- New dep	High	Best
Option B	+ Familiar	- Slow	Medium	Good
Option C	+ Feature-rich	- Complex	Low	Poor

Phase 3: Document

Record decisions in ADR format for future maintainers.

Quick Decision Record:

## Decision: [Title]

**Status**: Proposed | Accepted | Deprecated

**Context**: [Why this decision is needed]

**Decision**: [What we chose]

**Rationale**: [Why - connect to criteria]

**Trade-offs Accepted**: [What we gave up]

See DECISION-RECORD.md for full ADR format, consequences, and dependency tracking.

constraints-and-decisions.md Output

Decisions go in constraints-and-decisions.md with this structure:

# Constraints and Decisions: {feature_id}

## Summary

| ID | Decision | Choice | Rationale |
|----|----------|--------|-----------|
| D-001 | Auth mechanism | JWT | Stateless, scalable |
| D-002 | Session storage | PostgreSQL | Existing stack |

---

## Decision 1: [Title]

[Full decision record]

---

## Dependencies

| Decision | Depends On | Impacts |
|----------|------------|---------|
| D2 | D1 | Session table schema |

Brownfield Alignment

Always check existing stack first:

Scenario	Alignment	Action
Existing dep solves problem	High	Prefer reuse
New dep, same ecosystem	Medium	Document justification
New dep, different ecosystem	Low	Strong justification needed
Conflicting with existing	None	Avoid or escalate

Quality Checklist

Before finalizing:

Evaluation:

• At least 2-3 alternatives considered
• Criteria weighted by project context
• Each option has pros/cons
• Brownfield alignment assessed

Documentation:

• Context explains WHY decision is needed
• Rationale connects to specific criteria
• Trade-offs explicitly documented
• Constitution alignment checked
• Dependencies between decisions mapped

Common Mistakes

Single Option "Evaluation"

❌ "We evaluated Option A and chose it" ✅ "We compared Option A, Option B, and Option C against weighted criteria"

Shiny Object Syndrome

❌ Choosing newest technology because it's trending ✅ Require strong justification for unfamiliar dependencies over existing stack

Vague Rationale

❌ "We chose JWT because it's better" ✅ "We chose JWT because: stateless (fits our scale), team familiarity (3/4 devs), ecosystem support"

Ignoring Team Skills

❌ Choosing Rust for a Python team without accounting for learning curve ✅ Weight team familiarity criterion appropriately in evaluation matrix

Missing Trade-offs

❌ Only listing positives of chosen option ✅ Explicitly document what was given up: "Trade-off: JWT requires token refresh handling"

Orphan Decisions

❌ Decisions documented in isolation ✅ Map decision dependencies: "D2 (session storage) depends on D1 (auth mechanism)"

Constitution Blindness

❌ Making decisions that violate project principles ✅ Check alignment with constitution before finalizing