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12 March 2024

7 Min. Read

API Failures

Top Reasons for API Failures

Top Reasons for API Failures

Key Highlights

In this blog, we cover following key highlights

  1. Correct API key assignments enhance user access authorization and functionality.

  2. Secure key management systems protect against unauthorized data access.

  3. Token authentication and encrypted session management bolster data security.

  4. Proxy APIs for data caching and regular updates prevent access issues due to expiring APIs.

It's hard, expensive, and time-consuming to build your own API test suite. This whitepaper shows how to create a rigorous, no-code API testing suite that catches all major bugs before release.

Application Programming Interfaces (APIs) are the backbone of modern software development, facilitating seamless interactions between different systems and services. However, APIs can sometimes fail, leading to disruptions in service and impacting both developers and end-users.

Understanding API Failures

An API failure is not just a technical error; it's a break in the contract between the API and its consumers.

  • When developers integrate an API into their applications, they rely on it to behave as documented.

  • Failures disrupt this expectation, potentially causing cascading effects in the applications that depend on the API.

For instance, consider a weather forecasting app that relies on an external API to fetch weather data. If this API fails to respond or returns inaccurate weather information, the app might display incorrect forecasts to its users, undermining its reliability and user trust.

What Are the Common API Error Codes?

When working with APIs, encountering error codes is inevitable. These error codes are standardized responses that indicate to the client what kind of issue the API has encountered.

Understanding these error codes is essential for both API developers and consumers to effectively diagnose and handle errors.

1. 4xx Client Errors

  • 400 Bad Request: The server cannot process the request due to a client error (e.g., malformed request syntax).

  • 401 Unauthorized: The request has not been applied because it lacks valid authentication credentials for the target resource.

  • 403 Forbidden: The server understood the request but refuses to authorize it.

  • 404 Not Found: The server can't find the requested resource. This is often used when the endpoint is valid but the resource itself does not exist.

  • 429 Too Many Requests: The user has sent too many requests in a given amount of time ("rate limiting").

2. 5xx Server Errors

  • 500 Internal Server Error: The server encountered an unexpected condition that prevented it from fulfilling the request.

  • 502 Bad Gateway: The server, while acting as a gateway or proxy, received an invalid response from the upstream server.

  • 503 Service Unavailable: The server is not ready to handle the request, often due to maintenance or overload.

  • 504 Gateway Timeout: The server, while acting as a gateway or proxy, did not receive a timely response from the upstream server.

💡 Get free access on our comprehensive guide on “Application Errors that will happen because of API Failures”

Understanding these common API error codes and their implications can significantly improve the debugging process, making it easier to identify where the issue lies and how to resolve it. It's also important for API providers to use these status codes correctly and consistently, providing more detailed error messages when possible to facilitate easier troubleshooting.

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Reasons for API Failures

At its core, an API is a set of rules and protocols for building and interacting with software applications. APIs enable different software systems to communicate with each other, allowing them to share data and functionalities. An API failure can be caused by a range of issues, including:

  • Network Problems

  • Server Issues

  • Client-Side Errors

  • Security and Authorization Issues

  • Dependency Failures

  • Code Bugs

We now superficially understand the reasons on why APIs can fail, let’s dive deeper to understand these points better.

1. Poor API Design and Documentation

A well-designed API ensures ease of use, scalability, and maintainability. Poorly designed APIs with inadequate documentation can lead to misunderstandings, misuse, and integration difficulties.

Example: Consider an API endpoint that retrieves user details but requires a complex, undocumented JSON structure as input. This lack of clarity can lead to incorrect API calls.

// Poorly documented request structure
    "user_info": {
        "id": "123",
        "detail": "full"

How to fix this issue?

Follow industry standards like RESTful principles, use clear and consistent naming conventions, and provide comprehensive documentation using tools like Swagger (OpenAPI).

2. Authentication and Authorization Errors

APIs often fail due to incorrect handling of authentication and authorization processes, leading to unauthorized access or denial of legitimate requests.

Example: A common mistake is not validating JWT tokens properly in a Node.js application, leading to security vulnerabilities.

// Incorrect JWT validation
const jwt = require('jsonwebtoken');
const token = req.headers.authorization.split(' ')[1];
jwt.verify(token, process.env.SECRET_KEY, (err, decoded) => {
    if (err) {
        return res.status(401).send("Unauthorized");

How to fix this issue?

Implement robust authentication and authorization mechanisms, such as OAuth 2.0, and rigorously test these systems to prevent security breaches.

3. Dependency Failures

APIs often depend on other services or databases to work properly. However, these dependencies can sometimes cause problems. For example, if an external service or a database goes down or starts working slowly, it can lead to bottlenecks or even cause the API itself to fail. This means your app might not work as expected, or it might stop working altogether until these issues are fixed.

How to fix this issue?

To prevent these kinds of problems, one solution is to use tools that can simulate or "mock" these external dependencies. This includes mocking all the outbound calls whether it it to a third-party service, message systems like Kafka, or even a database.

By doing this, your application can be tested in a controlled environment without needing to rely on these external services being up and running. This helps ensure your app runs smoothly, even if there are issues with those external services.

💡 This allows for the autonomous testing of your application, without the necessity for external services to be online. Check this approach working here.

4. Rate Limiting and Throttling

Without proper rate limiting, APIs can be overwhelmed by too many requests, leading to failures and degraded performance.


An API without rate limiting can be easily overwhelmed by repeated requests, leading to server overload.

How to fix this issue?

Implement rate limiting using middleware in frameworks like Express.js to protect your API.

const rateLimit = require('express-rate-limit');

const apiLimiter = rateLimit({
    windowMs: 15 * 60 * 1000, // 15 minutes
    max: 100

app.use('/api/', apiLimiter);

5. Network Issues

Network problems, such as DNS failures, timeouts, and intermittent connectivity, can cause API calls to fail unpredictably.

How to fix this issue?

Implement retry mechanisms with exponential backoff and circuit breaker patterns to handle transient network issues gracefully.

6. Inefficient Data Handling

Inefficient handling of data, such as large payloads or unoptimized queries, can lead to slow response times and timeouts.

Example: Returning large, unpaginated data sets can cause performance issues.

How to fix this issue?

Implement pagination and data filtering to minimize the data transferred in each request.

app.get('/api/users', (req, res) => {
    const { page, limit } = req.query;
    // Implement pagination logic here

7. Versioning Issues

API versioning issues can arise when updates are made without backward compatibility, potentially breaking existing integrations.

How to fix this issue?

Use API versioning strategies (URL, header, or media type versioning) to manage changes and deprecations gracefully, ensuring backward compatibility.

8. Lack of Monitoring and Logging

Without proper monitoring and logging, diagnosing API failures can be challenging, leading to prolonged downtimes.

How to fix this issue?

Implement comprehensive logging and use monitoring tools to track API health, usage patterns, and error rates in real time.

Identifying and Handling API Failures

Effective error handling is crucial for mitigating the impact of API failures. Applications should implement strategies to detect and respond to failures gracefully, such as:

  • Timeouts: Setting timeouts ensures that an application does not wait indefinitely for an API to respond, allowing it to recover from temporary network or server issues.

  • Retries: Implementing retry logic, with exponential backoff, can help overcome transient errors or temporary unavailability of the API.

  • Error Handling: Properly handling HTTP status codes and parsing error messages returned by the API can help diagnose issues and take appropriate action.

  • Fallbacks: Where possible, applications should have fallback mechanisms, such as using cached data or default values, to maintain functionality even when an API is unavailable.

  • Monitoring and Alerts: Continuously monitoring API health and performance, and setting up alerts for failures, can help detect and address issues proactively.

  • Proper API Testing in place: This involves a comprehensive approach to testing APIs to anticipate and mitigate potential failures effectively. Doing so not only improves the reliability and performance of APIs but also safeguards the user experience by minimizing disruptions caused by unforeseen issues.

How can HyperTest help in identifying potential API failures?

In line with this, our tool, HyperTest, can help you catch all the critical bugs before it slips away into production. It is designed to deeply integrate with your application through a SDK, allowing it to carefully capture both incoming and outgoing interactions.

  • This level of integration facilitates a detailed understanding of how your application communicates and interacts with various components and external services.

  • HyperTest operates in two primary modes: RECORD and REPLAY.

    • The RECORD mode is instrumental in the initial phase of the testing lifecycle. It captures real interactions, which can then be used to automatically generate test cases. This not only streamlines the test case creation process but also ensures that the tests are reflective of real-world scenarios, thereby enhancing their effectiveness.

    • The REPLAY mode, is essential for isolation testing of applications. It allows the application to be tested in a controlled environment by replaying the interactions captured during the RECORD phase. This mode is particularly useful for identifying and handling API failures, as it enables developers to simulate various scenarios and observe how the application behaves in response to specific conditions without the need for external services to be active.

This comprehensive testing approach is key to identifying potential API failures early and implementing the necessary measures to handle them effectively, thereby enhancing the overall reliability and performance of your software applications.

Frequently Asked Questions (FAQs)

1. What is a API failure?

An API failure occurs when the intended software interface malfunctions, disrupting data exchange between applications due to issues like server errors or connectivity problems.

2. How do you handle API failures?

In the event of API failures, implementing robust error handling is crucial. This involves using appropriate status codes, logging detailed error messages, and implementing retry mechanisms to ensure resilience.

3. What is an example of an API error?

An example of an API error is receiving a 404 status code, indicating that the requested resource was not found on the server.
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