Hiring API Engineers: The Complete Guide

What API Engineers Actually Do

API Engineers are responsible for creating the "contracts" between software systems. When a mobile app fetches user data, when a partner integrates with your platform, or when microservices communicate—API Engineers design and maintain those interfaces. Their work determines whether developers love or hate working with your platform.

Unlike general backend engineers who might build APIs as part of broader system work, API Engineers focus specifically on the interface layer. They think about consistency across endpoints, backward compatibility, error message clarity, and how easy it is for someone to integrate without reading extensive documentation.

API Engineer vs Backend Engineer

A common question: when do you need an API Engineer versus a Backend Engineer with API experience?

When API Engineers Are Essential

• API-first companies: If your API IS the product (Stripe, Twilio, Plaid), you need specialists who obsess over developer experience.
• Platform teams: Building internal platforms that other teams consume requires API design expertise.
• Partner ecosystems: Extensive third-party integrations demand consistent, well-documented APIs.
• Developer tools: SDKs, CLI tools, and developer portals need dedicated API ownership.
• Public APIs: Any externally-facing API that will be consumed by unknown developers.

When Backend Engineers Suffice

• Internal microservices: Service-to-service APIs where you control both sides don't need the same polish.
• Application backends: Mobile/web app backends where the API serves a single frontend.
• Small teams: When you can't justify specialization, backend engineers can handle API work.
• Early-stage products: Before product-market fit, over-investing in API design may be premature.

REST vs GraphQL: Understanding the Landscape

API Engineers need deep expertise in multiple API paradigms. Understanding when to use each approach is crucial.

REST (Representational State Transfer)

REST remains the dominant API paradigm for good reason—it's simple, cacheable, and widely understood. Most API Engineers will work primarily with REST APIs.

REST strengths:

• HTTP semantics are universally understood
• Excellent caching at every layer (CDN, proxy, browser)
• Simple to debug with standard HTTP tools
• Mature tooling ecosystem (OpenAPI, Postman, curl)
• Clear resource-based mental model

REST challenges:

• Over-fetching (getting more data than needed)
• Under-fetching (requiring multiple requests)
• Versioning complexity as APIs evolve
• No standard query language

GraphQL

GraphQL solves specific problems REST struggles with, particularly for complex client applications with varied data needs.

GraphQL strengths:

• Clients request exactly the data they need
• Single endpoint reduces complexity
• Strong typing and introspection
• Excellent for mobile (bandwidth-sensitive)
• Real-time subscriptions built-in

GraphQL challenges:

• Caching is more complex
• Steeper learning curve
• Potential for expensive queries (N+1, deep nesting)
• Requires additional tooling
• Not as widely understood

What to Look For

Strong API Engineers understand both paradigms and can articulate when each is appropriate. They don't have religious preferences—they choose based on use case, team expertise, and client requirements.

Skills by Experience Level

Junior API Engineer (0-2 years)

Capabilities:

• Implement endpoints following established patterns
• Write API documentation with guidance
• Understand REST principles and HTTP semantics
• Handle authentication integration
• Write basic API tests

Learning areas:

• API design patterns and best practices
• Versioning and deprecation strategies
• Performance optimization
• Developer experience principles
• SDK development

Mid-Level API Engineer (2-5 years)

Capabilities:

• Design new APIs with minimal guidance
• Own documentation and developer guides
• Implement rate limiting and throttling
• Handle backward compatibility
• Create OpenAPI specifications
• Debug integration issues

Growing toward:

• API strategy and governance
• SDK architecture
• Developer relations
• Platform-wide consistency
• Complex versioning scenarios

Senior API Engineer (5+ years)

Capabilities:

• Define API strategy and standards
• Lead API design reviews
• Architect API gateway solutions
• Manage API lifecycle and deprecation
• Build SDK frameworks
• Drive developer experience initiatives

Demonstrates:

• Developer empathy and advocacy
• Cross-functional leadership
• Technical writing excellence
• Strategic thinking about platforms
• Incident management for API issues

Core Technical Skills

Must Evaluate

1. API Design Principles

• Resource modeling and naming conventions
• HTTP method semantics (idempotency, safety)
• Error handling and status codes
• Pagination strategies (cursor vs offset)
• Query parameters vs path parameters
• Request/response payload design

2. Documentation Expertise

• OpenAPI/Swagger specification
• Writing developer guides and tutorials
• Code samples in multiple languages
• Interactive documentation tools
• Changelog and migration guides

3. Authentication & Security

• OAuth 2.0 flows and best practices
• API key management and rotation
• JWT implementation and validation
• Rate limiting and abuse prevention
• CORS and security headers

4. Versioning Strategies

• URL versioning vs header versioning
• Backward compatibility maintenance
• Deprecation timelines and communication
• Breaking vs non-breaking changes
• API evolution best practices

5. Performance & Reliability

• Response time optimization
• Caching strategies (ETag, Cache-Control)
• Rate limiting implementation
• Circuit breakers and fallbacks
• Monitoring and alerting for APIs

Differentiate Mid from Senior

Senior API Engineers can:

• Define company-wide API standards and governance
• Lead design reviews and provide feedback
• Anticipate integration challenges before they occur
• Build tooling to improve API development
• Manage complex deprecation scenarios
• Create SDKs and client libraries
• Interface with external developers and partners

Where to Find API Engineers

High-Signal Sources

• API-first companies: Alumni from Stripe, Twilio, Plaid, SendGrid understand API excellence
• Platform teams: Engineers from companies with extensive partner ecosystems
• Open source: Contributors to API frameworks, documentation tools, or SDK projects
• Technical writing: Engineers who write blog posts about API design
• Developer advocates: Often have deep API design backgrounds

Companies Known for API Excellence

Communities & Events

• API The Docs (documentation conferences)
• Platform Engineering community
• GraphQL Summit
• OpenAPI Initiative
• Developer relations communities
• Technical writing communities

Interview Focus Areas

API Design Exercise

"Design an API for a notification system that supports email, SMS, and push notifications"

• Look for: resource modeling, consistent naming, versioning consideration, error handling
• Red flag: Jumps straight to implementation without discussing contracts

Developer Experience

"How would you improve the developer experience for this existing API?" (provide example)

• Look for: documentation gaps, error message clarity, consistency issues, SDK opportunities
• Red flag: Only focuses on technical implementation, ignores consumer experience

Backward Compatibility

"We need to add a breaking change to a public API. How do you handle this?"

• Look for: deprecation timeline, migration guides, version strategy, communication plan
• Red flag: "Just push the change and document it"

Error Handling Philosophy

"How do you design error responses for APIs?"

• Look for: consistent error format, helpful messages, error codes, debugging information
• Red flag: Generic errors without actionable guidance

Common Hiring Mistakes

1. Treating API Work as "Just Backend"

API engineering requires specific skills around developer experience, documentation, and interface design. Don't assume strong backend engineers automatically understand API design principles. Look for specific API experience.

2. Ignoring Documentation Skills

API Engineers must write—a lot. Technical writing is a core skill, not a nice-to-have. Evaluate their ability to explain complex concepts clearly. Review their past documentation work.

3. Over-Indexing on Framework Knowledge

Express vs FastAPI vs Spring matters less than API design fundamentals. Strong API Engineers can design excellent APIs regardless of framework. Focus on principles over specific tooling.

4. Skipping Developer Experience Questions

Ask how they think about the developers who consume their APIs. Great API Engineers advocate for external developers. If they only talk about implementation, they may be backend engineers, not API specialists.

5. Not Testing Writing Ability

Include a writing exercise in your interview process. Ask them to document an API or explain a concept. API Engineers who can't write clear documentation will create frustrating APIs.

Recruiter's Cheat Sheet

Resume Green Flags

• Experience at API-first companies (Stripe, Twilio, Plaid)
• Mentions developer experience or DX focus
• Created API documentation or developer portals
• Built SDKs or client libraries
• Worked on public or partner-facing APIs
• Contributed to OpenAPI specs
• Technical writing or blogging about APIs
• Developer advocacy or relations experience

Resume Yellow Flags

• Generic "built APIs" without context
• No mention of documentation or developer experience
• Only worked on internal microservice APIs
• No versioning or backward compatibility experience
• Focuses purely on implementation, not design
• No evidence of consuming APIs, only building them

Technical Terms to Know