Rate limit error responses in Rest API - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the HTTP status code returned for a rate limit error?

When a REST API enforces rate limiting and a client exceeds the allowed number of requests, what HTTP status code should the server return?

A 200 OK

B 429 Too Many Requests

C 500 Internal Server Error

D 403 Forbidden

💡 Hint

Think about the standard HTTP status code specifically designed for rate limiting.

The HTTP status code 429 Too Many Requests is the standard response when a client has sent too many requests in a given amount of time.

❓ Predict Output

intermediate

What header informs the client about when to retry after rate limiting?

Which HTTP response header tells the client how many seconds to wait before making another request after hitting a rate limit?

A Retry-After

B X-RateLimit-Reset

C Content-Type

D Authorization

💡 Hint

This header is part of the HTTP standard and indicates wait time.

The Retry-After header tells the client how many seconds to wait before retrying the request.

🧠 Conceptual

advanced

Why is it important to include rate limit headers in error responses?

Why should a REST API include headers like Retry-After or X-RateLimit-Remaining in responses when rate limiting is applied?

A To help clients understand when they can safely retry requests and avoid unnecessary failures

B To increase server load by making clients send more requests

C To hide the rate limit policy from clients

D To make responses larger for better network utilization

💡 Hint

Think about how clients can behave better with more information.

Including rate limit headers helps clients know when to retry and how many requests remain, improving user experience and reducing server overload.

❓ Predict Output

advanced

What is the typical JSON body content of a rate limit error response?

Given a REST API returns a 429 status code, which JSON response body best informs the client about the rate limit error?

A {"error": "Invalid API key"}

B {"message": "Success", "data": []}

C {"status": 200, "error": null}

D {"error": "Rate limit exceeded", "retry_after": 30}

💡 Hint

Look for a message about rate limiting and a retry time.

The JSON body should clearly state the error and provide a retry time in seconds to guide the client.

🔧 Debug

expert

Identify the error in this rate limit middleware code snippet

This code snippet is intended to return a 429 error with a Retry-After header when the client exceeds the rate limit. What is the error?

Rest API

function rateLimit(req, res, next) {
  if (req.requests > 100) {
    res.status(429);
    res.set('Retry-After', '60');
    res.send({ error: 'Rate limit exceeded', retry_after: 60 });
    return;
  }
  next();
}

A The status code 429 is incorrect for rate limiting

B The Retry-After header value must be a date string, not a number

C The middleware calls next() even after sending a response, causing headers to be sent twice

D The error message should be sent as plain text, not JSON

💡 Hint

Think about what happens after res.send() is called in middleware.

Calling next() after sending a response causes the next middleware to run and may try to send another response, leading to errors.