The Top 25 HTTP POST Request Interview Questions for Aspiring Developers

As a developer, having a strong grasp of HTTP and RESTful APIs is crucial for building effective web applications. One of the most common HTTP methods used in APIs is the POST request, which submits data to a server. Nailing questions about POST requests during a technical interview demonstrates your understanding of core development concepts.

In this comprehensive guide, we’ll explore the top 25 POST request interview questions frequently asked of developers. Mastering these questions will help you stand out in the recruiting process and land your dream dev job!

1. What is the difference between GET and POST requests?

GET and POST represent the two main HTTP methods for sending data between clients and servers.

• GET requests retrieve data from the server. The parameters are appended to the URL, so they are visible to users and limited in length. GET is used for idempotent operations with no side effects.

• POST submits data to the server for processing. The data is encapsulated in the request body rather than the URL. This allows sensitive information to be sent securely. POST is used for non-idempotent create update or delete operations that change server state.

2. When should developers use POST instead of GET?

Use POST when

• Submitting sensitive data like passwords that should not appear in URLs
• Sending large amounts of data exceeding maximum URL length
• Creating resources or modifying data which changes server state
• Supporting complex data structures beyond simple key-value pairs
• Data should be obscured from users for privacy

GET should only be used for read-only idempotent data retrieval.

3. What are some common POST request headers?

Some frequently used request headers for POST methods:

• Content-Type – Specifies the media type of request body
• Content-Length – Defines body length in bytes
• Authorization – Contains credentials for HTTP authentication
• User-Agent – Identifies client details like browser and OS
• Accept – Specifies acceptable response formats

Headers provide critical metadata about the request.

4. How are parameters sent in a POST request?

POST parameters are sent in the body of the HTTP request. The body accepts various formats like JSON, XML, or www-url-form-encoded. The Content-Type header signals the format.

Sending parameters in the body keeps the URL clean and allows complex data structures beyond name-value pairs. There is also no size limit.

5. What status codes should POST return?

Common status code responses to POST requests:

• 201 Created – Resource successfully created
• 200 OK – Request succeeded (non-idempotent)
• 204 No Content – Request processed but no info to return
• 400 Bad Request – Malformed syntax or invalid data
• 401 Unauthorized – Authentication required
• 403 Forbidden – Server refuses to authorize
• 404 Not Found – Invalid resource URI

2XX = success, 4XX = client error, 5XX = server error

6. How do you handle file uploads via POST?

To handle file uploads in POST:

1. Set form encoding type to multipart/form-data
2. Check and validate files on server before saving
3. Accept only required file types and size
4. Save file to appropriate directory on server
5. Store file metadata like path in database
6. Return URL of uploaded file to client

Follow security best practices when accepting files.

7. What are some advantages of POST over GET?

Advantages of using POST instead of GET:

• POST hides parameters in body, keeping sensitive data secure
• No limits on data length or types
• Ideal for non-idempotent create, update, delete operations
• Avoid placing large data loads in URLs
• More extensible for complex operations and data
• Enables web APIs that alter server state

8. How do cookies work with POST?

Cookies store session data on the client side and get automatically attached to subsequent requests made to the same server.

For POST methods, the client sends cookies previously set by the server via the Cookie request header. The server can then read the cookies to maintain user state.

It is important to protect against cross-site scripting by setting the HttpOnly cookie flag on sensitive cookies.

9. How does CORS affect POST requests?

CORS (Cross-Origin Resource Sharing) allows POST requests from foreign domains provided the server grants permission.

For “non-simple” requests like POST, an OPTIONS preflight request is made to check access. If permitted, the actual POST is sent.

Using CORS properly ensures security while enabling cross-domain AJAX requests needed for modern web apps.

10. What are best practices for POST security?

To secure POST requests:

• Use HTTPS – Encrypts traffic against sniffing
• Hash/salt passwords – Protects sensitive data
• Validate user input – Prevents injection attacks
• Use authentication tokens – Verifies user identity
• Limit payload size – Avoids overload attacks
• Implement CORS if needed – Enables safe cross-domain requests

Defense in depth is key for robust POST security.

11. How does a frontend JavaScript app make POST AJAX requests?

Common ways for JavaScript apps to send POST AJAX requests:

• XMLHttpRequest object – Low level API for AJAX
• jQuery AJAX methods – Helper methods like $.post()
• Fetch API – Modern alternative using Promises
• Axios – Popular third-party library for AJAX

These allow async requests without full page refreshes.

12. What are some tools to test POST endpoints?

Useful tools for testing POST API endpoints:

• Postman – Allows easily sending arbitrary POST requests
• cURL – Sends POST from command line for automation
• Chrome DevTools – Network tab monitors requests directly
• JMeter – Open source load testing tool for performance
• Swagger – Auto-generates UI for testing API endpoints

Automated testing ensures POST endpoints function properly.

13. Should POST requests be idempotent? Why?

POST requests should generally NOT be idempotent, meaning repeated identical requests should produce new results each time. This is because POST is most commonly used for create operations that modify data.

For example, submitting the same POST request to create a new user should generate distinct new users per request. Non-idempotency is a desired behavior.

Making POST idempotent requires additional effort and limits use cases.

14. What are some scenarios to use synchronous vs asynchronous POST?

Use cases for synchronous and asynchronous POST:

Synchronous

• User login – Require immediate server response
• Real-time transactions – Must wait for server confirmation
• Initial page load – May need data before rendering

Asynchronous

• Non-critical updates – Email/logging after main response
• Analytics pings – Doesn’t need immediate response
• Background data sync – Improve user experience

Evaluate requirements to pick appropriate approach.

15. How can you improve POST performance?

Strategies for improving POST API performance:

• Use HTTP/2 – Multiplexing and header compression
• Compress request data – Faster transmission
• Decrease payload size – Avoid overhead
• Cache requests – Avoid repeat processing
• Scale horizontally – Distribute load across servers
• Implement queues – Smooth traffic spikes

Benchmark and load test to identify bottlenecks.

16. What are conditional POST requests?

Conditional POSTs allow creating resources only if certain conditions are met, usually based on ETags or timestamps.

For example, POST /users with If-Match: “234abc” would only create the user if “234abc” matches the current ETag. This prevents duplicate simultaneous posts.

Conditional requests enable more robust, concurrent API design.

17. How are duplicate POST requests handled?

Duplicate POST requests that create the same resource should be handled gracefully:

• Check for unique constraint violations like duplicate usernames
• Return error response like 409 Conflict
• Implement “idempotency keys” to maintain consistency
• Consider making endpoint idempotent if appropriate
• Clear and document expected behavior for clients

Ideally duplicates would be prevented, but robust handling is needed.

18. When is HTTP PATCH preferable to POST?

PATCH allows partially updating resources while POST replaces resources completely.

Use PATCH when:

• Updating a subset of properties
• Making frequent updates to existing data
• Optimizing performance by reducing payload size

PATCH reduces bandwidth usage compared to POST for partial updates.

19. What are the pros and cons of using JSON for POST bodies?

Pros:

• Wide programming language support
• Easy for humans to read
• Fast parsing compared to XML
• Can represent complex hierarchical data

Cons:

• Limited data types compared to XML
• No built-in validation mechanisms
• Less self-documenting than XML
• Security vulnerabilities if improperly handled

JSON provides a simple yet powerful transport format.

20. How can you use Postman to craft POST requests?

Postman makes it easy to manually test POST endpoints:

1. Define URL, headers, and body
2. Generate code