| name | software-craft |
| description | This skill should be used when making design decisions, evaluating trade-offs, assessing code quality, or when engineering judgment or code quality are mentioned. |
| metadata | {"version":"1.0.1"} |
Software Engineering
Engineering judgment - thoughtful decisions - quality code.
<when_to_use>
- Making architectural or design decisions
- Evaluating trade-offs between approaches
- Determining appropriate level of thoroughness
- Assessing when code needs refactoring
- Deciding when to ask vs proceed independently
- Balancing speed, quality, maintainability
NOT for: mechanical tasks, clear-cut decisions, following explicit instructions
</when_to_use>
Core engineering judgment framework.
User preferences trump defaults
CLAUDE.md, project rules, existing patterns always override skill suggestions.
Simplest thing that works
Start simple. Add complexity only when requirements demand.
- Boring solutions for boring problems
- Proven libraries over custom implementations
- Progressive enhancement over rewrites
Read before write
Understand existing patterns before modifying.
- Check how similar features implemented
- Follow established conventions
- Maintain consistency
Small, focused changes
One idea per commit, 20-100 LOC, 1-5 files.
- Easy to review/understand
- Lower bug risk
- Simpler to revert
- Faster feedback
Security awareness
Don't introduce vulnerabilities.
- Validate external input
- Parameterized queries
- Handle auth properly
- No secrets in code/logs
Know when to stop
Ship working code, don't gold-plate.
- Implement requirements, not assumptions
- No unrequested features
- No speculative abstraction
<type_safety>
Type safety across languages.
Core principle: Make illegal states unrepresentable. Type system should prevent invalid data at compile time, not runtime.
Hierarchy: Correct (type-safe) - Clear (self-documenting) - Precise (not overly broad)
Key patterns:
- Result types - Errors explicit in signatures, not hidden in exceptions
- Discriminated unions - Mutually exclusive states with discriminator field
- Branded types - Distinct types for domain concepts (user ID vs product ID)
- Parse, don't validate - Transform untyped to typed at boundaries, trust types internally
See type-patterns.md for detailed concepts.
Load typescript-fieldguide/SKILL.md for TypeScript implementations.
</type_safety>
<decision_framework>
Systematic approach to engineering choices.
Understand before deciding
- What problem being solved?
- What constraints exist?
- What's already in codebase?
- What patterns does project use?
Consider trade-offs
No perfect solutions:
- Speed vs robustness
- Simplicity vs flexibility
- Consistency vs optimization
- Implement time vs maintain time
Recognize good-enough
Perfect is enemy of shipped:
- Meets requirements?
- Maintainable by team?
- Tested adequately?
- Can improve incrementally?
If yes to all - ship it.
Document significant choices
Non-obvious decisions: comment why, note trade-offs, link discussions, flag assumptions.
</decision_framework>
<when_to_ask>
Balance autonomy with collaboration.
Proceed independently:
- Task clear and well-defined
- Approach follows existing patterns
- Changes small and localized
- Requirements fully understood
- No security/data integrity risks
Ask questions:
- Requirements ambiguous
- Multiple approaches, unclear trade-offs
- Changes affect architecture
- Security/compliance implications
- Unfamiliar domain/technology
Escalate immediately:
- Security vulnerabilities discovered
- Data corruption/loss risk
- Breaking changes to public APIs
- Performance degradation detected
Don't guess on high-stakes decisions.
</when_to_ask>
<code_quality>
Standards separating good from professional code.
Type safety: Make illegal states unrepresentable via discriminated unions, branded types.
Error handling: Every error path needs explicit handling. No silent failures.
Naming: Functions=verbs (calculateTotal), variables=nouns (userId), booleans=questions (isValid).
Function design: One thing well. 10-30 lines typical, max 50. 3 params ideal, max 5. Pure when possible.
Comments: Explain why, not what.
See code-quality-patterns.md for examples.
</code_quality>
When and how to improve existing code.
Refactor when:
- Adding feature reveals poor structure
- Code duplicated 3+ times
- Function exceeds 50 lines
- Naming unclear/misleading
- Tests difficult to write
Don't refactor when:
- Code works and won't be touched
- Time-critical delivery in progress
- No test coverage to verify
- Scope creep from main task
- Just preference, no clear benefit
Guidelines:
- Have tests first (or write them)
- One refactoring at a time
- Keep tests passing throughout
- Commit refactors separately from features
- Don't change behavior
Testing philosophy.
Test the right things:
- Public interfaces, not implementation
- Edge cases and error paths
- Critical business logic
- Integration points
- Security boundaries
Don't over-test:
- No tests for trivial getters/setters
- Don't test framework behavior
- Avoid brittle implementation-coupled tests
Coverage targets:
- Critical paths: 90%+
- Business logic: 80%+
- Utility functions: 80%+
- Overall: 70%+
Low coverage acceptable for: config, type definitions, framework boilerplate.
Balance optimization with delivery.
Premature optimization is root of evil
- Make it work first
- Make it right second
- Make it fast only if needed
Optimize when:
- Measured performance issue exists
- User experience degraded
- Resource costs excessive
- Profiler shows clear bottleneck
Before optimizing:
- Measure current performance
- Set target metrics
- Profile to find bottleneck
- Optimize specific bottleneck
- Measure improvement
- Document trade-offs
Don't optimize based on gut feeling or without measurement.
Security mindset for all code.
Input validation: Validate all external input, sanitize before processing, allowlists over blocklists.
Auth: Never trust client-side checks, verify on server, use proven libraries, don't roll your own crypto.
Data handling: Never log sensitive data, hash passwords (bcrypt/argon2), parameterized queries, strict file upload validation.
Dependencies: Keep updated, review advisories, minimize count, audit before adding.
Red flags to escalate: Payment info, user credentials, health/financial data, encryption implementation, session management.
<anti_patterns>
Common mistakes to avoid.
Over-engineering: Building "might need" features, premature abstraction, excessive config, enterprise patterns for simple problems.
Fix: YAGNI. Build for today.
Under-engineering: No error handling, no input validation, ignoring edge cases, copy-paste over functions.
Fix: Basic quality isn't optional.
Scope creep: "While I'm here...", refactoring unrelated code, adding unrequested features.
Fix: Stay focused. File issues for unrelated work.
Guess-and-check: Random solutions, copying without understanding, no root cause investigation.
Fix: Systematic debugging. Understand before changing.
Analysis paralysis: Endless design discussions, researching every option, waiting for perfect.
Fix: Good enough + shipping > perfect + delayed.
</anti_patterns>
Senior engineer collaboration.
Clear issues/PRs: Context (problem), approach (solution), trade-offs (alternatives), testing (verification), impact (risks).
Code review: Focus on correctness/clarity/security. Suggest, don't demand perfection. Approve when good enough.
When blocked: Try 30 min self-unblock, gather context, ask specific question with context, propose solutions.
Saying no: "That would work, but have you considered X?" / "This introduces Y risk. Can we mitigate with Z?"
Back opinions with reasoning. Stay open to being wrong.
<workflow_integration>
Connect with other outfitter skills.
With TDD: Senior judgment decides what's worth testing. TDD skill provides how.
With debugging: Senior judgment decides if worth fixing now. Debugging skill provides systematic investigation.
With dev-* skills: Software engineering provides the "why" and "when". dev-* skills provide the "how" for specific technologies (typescript-fieldguide, react-fieldguide, hono-fieldguide, bun-fieldguide).
</workflow_integration>
ALWAYS:
- Read
CLAUDE.md and project rules first
- Follow existing codebase patterns
- Make small, focused changes
- Validate external input
- Handle errors explicitly
- Test critical paths
- Document non-obvious decisions
- Ask when uncertain on high-stakes
NEVER:
- Add features not in requirements
- Ignore error handling
- Skip input validation
- Commit secrets or credentials
- Guess on security decisions
- Refactor without tests
- Optimize without measuring
- Over-engineer simple solutions
Complements other outfitter skills:
Core Practices:
Development Skills (load for implementation patterns):
Detailed Patterns:
Standards:
