Senior Fullstack Developer

Senior Fullstack Developer

When to Use

• Senior-owned vertical features with higher design bar
• PR review for authz, data layer, and frontend architecture
• Production debugging across app layers with mentorship-level guidance

When NOT to Use

• Routine full-stack feature work at standard IC bar → fullstack-software-engineer
• Cross-team RFCs and service boundaries → senior-software-engineer
• Infrastructure or pipelines → infrastructure-engineer, devops

Related skills

Core Workflows

1. Feature delivery (vertical slice)

1. Clarify acceptance criteria and non-goals 2. Sketch API contract + UI states (loading, empty, error) 3. Implement backend with validation and authz checks first 4. Implement UI against contract; use typed client 5. Add tests: unit for logic, integration for API, e2e for critical path 6. Instrument logs/metrics for new endpoints 7. Ship behind flag if risky; document rollout and rollback

See `references/feature_delivery.md` for slice checklist and PR template.

2. API and data layer design

See `references/api_data_patterns.md` for pagination, idempotency, and transaction patterns.

3. Frontend architecture

• Prefer server components where data is read-heavy (Next.js App Router)
• Colocate state: server for fetch, client only for interaction
• Accessible components (labels, focus, contrast)
• Avoid premature abstraction; extract after second use

See `references/frontend_patterns.md` for forms, caching, and performance.

4. Quality and review

PR review focus: correctness, authz, input validation, N+1 queries, error paths, test coverage on changed lines.

Before merge: lint, typecheck, tests green; no secrets; migration plan if schema changed.

See `references/testing_quality.md` for test pyramid and flaky test handling.

5. Production debugging

1. Reproduce with correlation ID 2. Check recent deploys and feature flags 3. Trace logs → metrics → DB slow queries 4. Fix forward or rollback; add regression test

See `references/debugging_ops.md` for common failure modes.

When to load references

• End-to-end feature flow → references/feature_delivery.md
• APIs and databases → references/api_data_patterns.md
• React/Next UI → references/frontend_patterns.md
• Testing and review → references/testing_quality.md
• Prod debugging → references/debugging_ops.md

API and data patterns

Table of contents

1. REST conventions 2. Pagination 3. Idempotency 4. Migrations

REST conventions

• GET safe, PUT/PATCH idempotent where possible
• Use nouns for resources; avoid verbs in paths
• Return consistent error shape: { code, message, details? }

Pagination

Prefer cursor-based for large feeds; offset only for admin tools.

Idempotency

Accept Idempotency-Key header on POST that creates billable or external side effects.

Migrations

• Backward-compatible expand → deploy → contract
• Never drop column in same release as code stops reading it

Production debugging

Table of contents

1. Triage order 2. Common causes

Triage order

1. Correlation ID across logs and traces 2. Deploy timeline vs error spike 3. Feature flags and config changes 4. Dependency health (DB, cache, third-party API) 5. Resource saturation (CPU, connections)

Common causes

Feature delivery

Table of contents

1. Vertical slice checklist 2. PR description template

Vertical slice checklist

• [ ] Acceptance criteria met
• [ ] API contract documented or OpenAPI updated
• [ ] Authz on all new routes
• [ ] UI states: loading, empty, error
• [ ] Tests for happy path + main failure
• [ ] Feature flag if gradual rollout
• [ ] Rollback steps in PR or release notes

PR description template

## What
## Why
## How to test
## Risks / rollback
## Screenshots (if UI)

Frontend patterns

Table of contents

1. Next.js App Router 2. Forms 3. Performance

Next.js App Router

• Fetch on server by default; pass serializable props to client components
• Use loading.tsx and error.tsx boundaries
• Cache with explicit revalidate strategy

Forms

• Validate on client for UX; always validate on server
• Optimistic UI only when rollback is cheap

Performance

• Measure LCP, INP; lazy-load below-fold
• Avoid waterfall client fetches; batch where possible

Testing and quality

Table of contents

1. Test pyramid 2. What to test 3. Flaky tests

Test pyramid

What to test

• Authz matrix for new endpoints
• Edge cases in validation
• Regression for every production bug fix

Flaky tests

Quarantine with ticket; fix or delete within 2 sprints—do not retry indefinitely without investigation.