What does an API Engineer do?
API Engineers design, build, secure, and maintain the interfaces that connect products, services, and data. You turn business capabilities into reliable endpoints other teams and external partners can use.
Typical deliverables
- Well-designed REST/GraphQL/async APIs with clear contracts (OpenAPI/AsyncAPI)
- Design docs and RFCs for new or changed endpoints
- Authentication/authorization integration (e.g., OAuth2, JWT)
- Automated tests, CI/CD pipelines, and canary/blue-green deployments
- Developer docs, examples, and SDK stubs
- Dashboards and alerts for latency, error rate, and throughput
- SLOs, runbooks, and incident postmortems
Day-to-day work
- Discuss requirements with product and client developers
- Model resources, design endpoints, and review tradeoffs
- Write code, tests, and schemas; ship safely via CI/CD
- Monitor metrics and logs, tune performance, and handle incidents
- Improve developer experience: docs, samples, versioning strategy
Tools you might use
- Languages: Go, Node.js/TypeScript, Python, Java/Kotlin
- Frameworks: Express/Fastify, Spring Boot, FastAPI, Gin/Fiber
- Gateways: Kong, NGINX, API Gateway, Apigee
- Messaging: Kafka, RabbitMQ, SQS
- Infra: Docker, Kubernetes, Terraform
- Contracts/Testing: OpenAPI/AsyncAPI, Postman/Newman, Pact
Who this is for
- Backend developers who want to specialize in service interfaces and integration
- Full‑stack engineers seeking stronger API design, security, and reliability skills
- Data/Platform engineers who expose services to other teams or partners
- Career switchers comfortable with logical thinking and building systems
Prerequisites
- Comfortable with one backend language (e.g., JavaScript/TypeScript, Python, Go, or Java)
- Basics of HTTP, JSON, and Git
- Foundational understanding of databases (SQL or NoSQL)
Need a quick catch-up plan?
- Week 1: HTTP methods, status codes, headers; build a tiny REST endpoint
- Week 2: Basic SQL CRUD; containerize a service with Docker
- Week 3: Write unit tests and a simple CI workflow
Where you can work
- Industries: fintech, e‑commerce, SaaS, health, logistics, gaming, gov/edu
- Teams: platform/core services, partner integrations, mobile/backend APIs, data platform interfaces, public developer platforms
- Company sizes: startups (move fast, broader scope) to enterprises (scale, governance)
Hiring expectations by level
Junior (0–2 years)
- Implements endpoints from a design with guidance
- Writes unit tests, basic integration tests, and clear docs
- Understands HTTP, JSON, simple auth flows, and error handling
- Receives reviews; learns reliability basics and instrumentation
Mid-level (2–5 years)
- Owns end‑to‑end features from design to production
- Designs resource models, pagination, and versioning strategy
- Implements secure authz/authn, rate limiting, and safe migrations
- Introduces monitoring, SLOs, and on‑call readiness
Senior (5+ years)
- Leads API strategy across services; formalizes contracts and reviews
- Designs for scalability and reliability (backpressure, retries, idempotency)
- Champions developer experience, SDKs, and documentation standards
- Guides incident response, capacity planning, and cross‑team integration
Salary ranges
Approximate total compensation in USD. Varies by country/company; treat as rough ranges.
- Junior: $60k–$100k
- Mid-level: $90k–$140k
- Senior/Staff+: $130k–$200k+
- Contract: ~$40–$120/hour depending on scope and region
Skill map
- API Engineering Fundamentals: HTTP/1.1–2, REST patterns, JSON, OpenAPI, authentication basics
- API Design and Architecture: resource modeling, versioning, GraphQL vs REST vs async, pagination, errors
- API Security: OAuth2/OIDC, JWT, scopes, mTLS, secrets, threat modeling
- API Documentation & Developer Experience: docs, examples, SDKs, changelogs, deprecation
- Performance & Reliability: caching, concurrency, timeouts, retries, rate limits, backpressure
- Observability & Monitoring: logs, metrics, traces, SLOs, alerts, runbooks
- Data Integration & Consistency: transactions, outbox pattern, eventing, idempotency, schema evolution
- Testing & Quality: unit/integration/contract tests, test data, mocking, non‑breaking changes
- Platform & Delivery: containers, CI/CD, blue‑green/canary, gateways, infra‑as‑code
Learning path
- Start with Fundamentals
- Master HTTP methods, status codes, headers, caching semantics
- Write a tiny service: list/create/read/update/delete a resource
Mini task
Design a "Books" API. Define endpoints and JSON bodies. Add correct status codes and error shapes.
- Design & Architecture
- Model resources, choose pagination, and define error formats
- Decide REST vs GraphQL vs async for a feature and explain tradeoffs
- Security first
- Implement OAuth2 Authorization Code with PKCE
- Add scopes and role‑based access to sensitive endpoints
- Testing & Docs
- Write unit, integration, and contract tests against OpenAPI
- Publish docs with examples and a changelog
- Observability & Reliability
- Add structured logs, metrics (latency, error rate), and tracing
- Define an SLO and alerts; add idempotency and retries where safe
- Data Integration
- Use outbox pattern for reliable events
- Design bulk endpoints and partial success responses
- Platform & Delivery
- Containerize, set up CI/CD, and deploy with canary
- Expose via an API gateway with rate limiting and auth
Practical projects for your portfolio
- Public Todo API: REST API with OpenAPI contract, pagination, filtering, and ETags. Outcome: clean resource modeling and versioning.
- Payments Webhook Receiver: Verify signatures, ensure idempotency, and process events reliably. Outcome: robust async handling with retries and DLQ simulation.
- Bookstore GraphQL Gateway: Stitch data from two services. Outcome: schema design, N+1 avoidance, and caching.
- Observability Pack: Add metrics, structured logs, and tracing to an existing API. Outcome: dashboards and alerts with a runbook.
- Zero‑Downtime Migration: Ship a breaking field change as an additive migration plus deprecation plan. Outcome: backward compatibility story and rollout plan.
Project review checklist
- Clear OpenAPI/GraphQL schema and examples
- Automated tests (unit, integration, contract)
- Authn/authz coverage on sensitive routes
- SLI dashboards and at least one SLO
- Docs: quick start, errors, changelog, deprecation policy
Interview preparation checklist
- Explain idempotency and how you implemented it
- Walk through OAuth2/OIDC flows and common pitfalls
- Design an API: pick resource models, pagination, versioning, and errors
- Discuss tradeoffs: REST vs GraphQL vs async messaging
- Reliability: timeouts, retries, circuit breakers, backpressure
- Observability: what you log/measure and how you alert
- Rollouts: blue‑green vs canary; how you prevent breaking changes
- Security: threat modeling and least‑privilege scopes
Mini task: 30‑second API pitch
Describe an API you built: problem, key endpoints, security choice, and the biggest reliability decision you made.
Common mistakes and how to avoid them
- Inconsistent errors: Define a standard error shape; include code, message, and correlation ID.
- Over‑fetching/under‑fetching: Offer filters, sparse fieldsets, or GraphQL where appropriate.
- Breaking changes without a plan: Use additive changes, deprecate with dates, and support two shapes during rollout.
- Retries without idempotency: Require idempotency keys for POST‑like operations.
- No timeouts/backoff: Set timeouts, retries with jittered backoff, and circuit breakers.
- Underdocumented auth: Document scopes/roles with examples of allowed vs denied calls.
Next steps
- Pick one skill below and study for one focused week
- Build one small project alongside the study
- Take the exam to locate your gaps
Ready? Pick a skill to start in the Skills section below. When you feel confident, try the exam.