30 REST API Interview Questions for 2026

Practice 30 REST API interview questions on HTTP methods, status codes, auth, caching, pagination, versioning, and real design scenarios for 2026.

REST API interview questions: what interviewers are really testing

A REST API interview is not really a quiz about acronyms. It is a check on whether you understand how APIs behave in production.

At the basic level, interviewers want to know if you can explain REST, HTTP, and common status codes without wandering off. At the next level, they want to see whether you understand why choices like pagination style, auth method, caching strategy, or versioning scheme matter when real clients depend on your API.

That is why the best Rest Api Interview Questions in 2026 are rarely just definitions. They usually ask about real decisions: how you would design an endpoint, how you would avoid breaking clients, how you would handle retries safely, or how you would keep errors consistent.

If you keep that frame in mind, your answers will sound a lot less memorized.

REST API basics you should be able to answer cold

What REST is and what makes an API RESTful

REST stands for Representational State Transfer. In practice, interviewers care about a few core ideas:

Resources matter more than verbs in the URL.
The server should be stateless between requests.
Clients interact with resources through standard HTTP methods.
Responses should use standard HTTP semantics instead of inventing everything from scratch.

A RESTful API is usually organized around resources such as users, orders, or bookings, and each request carries enough context for the server to process it on its own.

A strong interview answer here is short. Define REST, mention statelessness, mention resources, and give a concrete example.

HTTP methods and when to use them

You should know the common HTTP methods and what they are for:

GET: read data
POST: create a new resource or trigger a non-idempotent action
PUT: replace a resource, or create it if the client supplies the identifier
PATCH: partially update a resource
DELETE: remove a resource
HEAD: like GET, but without the body
OPTIONS: ask what methods are supported, often useful for CORS

Two concepts matter here:

Safe methods do not change server state. GET and HEAD are the classic examples.
Idempotent methods can be repeated without changing the result after the first call. PUT and DELETE are idempotent. GET is also idempotent. POST usually is not.

If you mix up safe and idempotent, interviewers notice. It is an easy way to lose points for no good reason.

Status codes and request/response basics

Know the common families:

2xx: success
200 OK
201 Created
204 No Content
4xx: client-side problem
400 Bad Request
401 Unauthorized
403 Forbidden
404 Not Found
409 Conflict
422 Unprocessable Entity
429 Too Many Requests
5xx: server-side problem
500 Internal Server Error
502 Bad Gateway
503 Service Unavailable

Also know the difference between a resource and an endpoint:

A resource is the thing you are modeling.
An endpoint is the URL surface used to access it.

And remember the difference between path parameters and query parameters:

Path parameters usually identify a specific resource.
Query parameters usually filter, sort, or paginate results.

PUT vs POST, PUT vs PATCH

This comes up all the time.

POST is usually used to create a new resource or submit data to a collection endpoint.
PUT is used when the client knows the full target resource identity and wants to replace it.
PATCH is used for partial updates.

A clean way to answer:

Use POST to create a new booking under `/bookings`. Use PUT if the client already knows the booking ID and wants to replace the booking resource. Use PATCH if only one field, like status or date, changes.

If the interviewer pushes further, mention idempotency. PUT is generally idempotent. POST usually is not.

Authentication, authorization, and security questions

401 vs 403

This one is simple, but it trips people up.

401 Unauthorized means the client is not authenticated, or the credentials are missing or invalid.
403 Forbidden means the client is authenticated, but does not have permission.

A good shorthand: 401 is "who are you?" and 403 is "I know who you are, but you cannot do that."

Authentication methods for REST APIs

You should be able to explain the common options at a high level:

Basic Auth: simple username/password over HTTPS; fine for limited cases, not ideal for modern production APIs
JWT: a token format commonly used in stateless auth flows
OAuth 2.0 / OAuth 2.1: used when one service needs delegated access or third-party authorization flows

Interviewers do not usually want a full spec lecture. They want to know whether you understand the purpose of each one and where it fits.

JWT basics and common mistakes

JWT stands for JSON Web Token. It is often used to carry claims between client and server in a signed token.

What matters in interviews:

It is not encryption by default.
It is usually signed, not hidden.
The server should still validate it properly.
You should not treat it like a magic security feature.

If the interviewer asks about JWT security, stay practical. Mention token expiry, signing algorithms, revocation strategy, and storage concerns.

CORS and browser behavior

If your API is used by browsers, expect CORS questions.

Know this much:

Browsers enforce same-origin policy.
CORS lets a server tell the browser which cross-origin requests are allowed.
A preflight request happens before some cross-origin requests, usually when the method or headers are not simple.

A strong answer should mention that CORS is a browser enforcement issue, not an API authentication mechanism.

Token storage on the client

This question usually asks whether you understand trade-offs, not whether you memorized one "correct" answer.

Practical framing:

Avoid exposing tokens unnecessarily.
Be careful with XSS if storing tokens in browser-accessible storage.
Use HTTPS.
If the app design requires client storage, explain the trade-offs clearly.

The interviewer is usually checking whether you understand security risk, not whether you can repeat a blog post.

Design and implementation trade offs interviewers ask about

Pagination, filtering, sorting

This is one of the most common practical areas in REST interviews.

You should be ready to discuss:

Offset pagination
Easy to implement
Can get slower as offsets grow
Can behave poorly when the dataset changes during paging
Cursor-based pagination
Better for large or changing datasets
More stable for infinite scroll and feed-like experiences
Slightly more complex to implement and explain

Filtering and sorting usually belong in query parameters.

Example:

`/orders?status=paid&sort=-createdAt&limit=20`
`/users?role=admin&country=US`

If the data set is large, mention indexing and performance. If the data is mutable, mention consistency concerns.

API versioning

Interviewers like this topic because it shows whether you think about backward compatibility.

Common strategies include:

URL versioning, such as `/v1/users`
Header-based versioning
Query parameter versioning, though this is less elegant in many systems

What matters most is not the syntax. It is how you migrate from one version to another without breaking clients.

A strong answer should mention:

deprecation windows
backward compatibility
communication with consumers
gradual rollout instead of hard breaks

Caching and ETags

Caching is a classic interview topic because it touches both performance and correctness.

Know the basic ideas:

HTTP caching can reduce repeated work and improve latency.
`ETag` helps with conditional requests.
`If-None-Match` lets the server return `304 Not Modified` when content has not changed.

If you want to sound practical, explain that caching is not just about speed. It also reduces load and improves reliability when used correctly.

Rate limiting

This is a high-signal interview topic because it shows whether you think about abuse, fairness, and system stability.

What to mention:

Rate limiting protects APIs from overload and abuse.
Limits can be based on user, IP, token, tier, or route.
Responses often use 429 Too Many Requests.
`Retry-After` helps clients know when to try again.

If the interviewer asks how to design it, talk about policy, storage, distributed enforcement, and how you keep it fair across users.

Error handling

Good APIs do not just fail. They fail consistently.

A strong answer includes:

predictable status codes
stable error payloads
machine-readable error fields
human-readable message fields
enough context for debugging without leaking sensitive data

If you mention RFC 7807, keep it simple. Problem Details is a standard format for structured error responses. The point is consistency.

Idempotency in real systems

This matters a lot for payment-like APIs and retry-heavy workflows.

You should know:

Idempotent operations can be safely repeated.
Retries happen in the real world.
Network timeouts do not mean the action did not happen.

A classic example is an idempotency key for a payment endpoint. If the client retries, the server should not create duplicate charges.

That is the kind of answer experienced interviewers like because it connects HTTP theory to production behavior.

Scenario based REST API interview questions

Design a REST API for a hotel booking system

This is a very common design prompt because it is simple to state and rich enough to test judgment.

A good approach:

identify core resources: hotels, rooms, bookings, users, payments
define clear endpoints
think about availability and conflict handling
use proper status codes
consider idempotency for booking creation
think through cancellation and modification flows

One good follow-up is conflict handling. If two users try to book the same room, what happens? A thoughtful answer might use `409 Conflict` or a similar response depending on the workflow.

How would you design a search API with complex filtering?

This question tests whether you can design for usability and performance.

Good things to cover:

query parameters for filters
sorting fields
pagination
clear defaults
constraints to avoid overloading the API with too much freedom
relevance and performance trade-offs for search

If filters become deeply nested or highly expressive, it is fair to mention that REST may start to feel awkward and that you need to balance flexibility with simplicity.

How do you handle long running operations?

Not every operation should finish synchronously.

A practical design usually includes:

a job resource
an accepted response, often `202 Accepted`
a polling endpoint
status fields like queued, running, succeeded, failed
optional callbacks or webhooks if the system supports them

This is a good place to show that you understand asynchronous design without drifting away from REST.

How do you migrate an existing API without breaking clients?

This is one of the best experienced-candidate questions because it tests production judgment.

A good answer should mention:

versioning
backwards-compatible changes first
deprecation notices
dual support during transition
telemetry on old-client usage
clear documentation

The interviewer wants to know whether you can evolve an API without forcing every consumer to coordinate at once.

How would you implement rate limiting for different user tiers?

This is where theory meets business logic.

You can explain:

free users get lower limits
paid tiers get higher limits
enterprise tiers may get custom rules
per-route limits may differ from global limits
abuse detection should still apply across tiers

If you mention fairness, you sound grounded. If you mention only "just add a limiter," you sound like you have not thought about production traffic.

Fresher vs experienced candidate: how to level your answers

For fresher candidates

If you are early in your career, keep the answers tight and correct.

Focus on:

what REST is
HTTP methods
status codes
statelessness
basic auth concepts
clear examples

Do not try to fake deep production experience if you do not have it. A clean, accurate answer is better than a flashy one.

For experienced candidates

If you have real backend or platform experience, go deeper.

Focus on:

trade-offs
failure modes
scaling concerns
backward compatibility
retries and idempotency
operational concerns like caching, rate limiting, and monitoring

You are being evaluated on judgment as much as knowledge.

How to answer without sounding memorized

A simple structure works well:

Define the concept.
Explain why it matters.
Give a real-world example.

That structure works for almost every REST interview question and keeps you from sounding like you are reading from a glossary.

Common mistakes to avoid in REST API interviews

A few mistakes show up again and again:

giving definitions without examples
mixing up safe and idempotent methods
ignoring auth, caching, versioning, or error handling
using vague answers for scenario questions
treating REST as a religion instead of a set of practical trade-offs
forgetting that browsers, retries, and real clients create edge cases

If you can explain a trade-off clearly, you are already ahead of most candidates.

Quick practice: 30 most asked REST API interview questions

Here is a compact list to use as a drill sheet.

Fundamentals

What is REST?
What makes an API RESTful?
What is a resource in REST?
What is the difference between a resource and an endpoint?
What does stateless mean in REST?
What is the difference between REST and SOAP?

HTTP and status codes

When do you use GET, POST, PUT, PATCH, and DELETE?
What is the difference between PUT and POST?
What is the difference between PUT and PATCH?
What are safe methods?
What are idempotent methods?
What is the difference between 401 and 403?
When would you return 409 Conflict?
When would you return 422 Unprocessable Entity?
What does 429 Too Many Requests mean?

Security

What authentication methods are used for REST APIs?
What is JWT?
What is the difference between OAuth 2.0 and OAuth 2.1 at a high level?
What is CORS?
What is a CORS preflight request?
Where should tokens be stored on the client?

Design and scenario questions

How would you design pagination for a large dataset?
When would you use cursor-based pagination?
How do you design filtering and sorting?
How would you version an API?
How do you migrate from v1 to v2 without breaking clients?
How do you handle long-running operations?
How do you design error responses consistently?
How do you implement rate limiting?
How would you design a hotel booking API?
How would you implement idempotency for a payment endpoint?

Final thoughts

The best way to prepare for Rest Api Interview Questions is not to memorize 30 definitions. It is to practice explaining the same concepts in different contexts: basic, practical, and scenario-based.

If you want to tighten your answers before the interview, Verve AI can help you rehearse them live. Use the mock interview flow or the interview copilot to practice answering REST questions out loud, then refine the parts that feel fuzzy. That is usually more useful than staring at another cheat sheet.

If you can answer the basics cleanly and handle the trade-offs without drifting, you will be in good shape.

Verve AI

Interview Report

Top REST API Interview Questions: 30 Most Asked for 2026