How to Do API Testing Manually and Why Should You

How to Perform API Testing Manually: a Roadmap

Plans are nothing. Planning is everything. The first thing you need to do before manual API testing is to prepare for it. That includes setting up your environments, dividing tasks between relevant specialists, selecting tools, and more.

Here’s a brief step-by-step guide from our QA engineers on everything your API checks will need.

Define the Testing Scope

Start by defining the scope of your testing. Identify the key features and API endpoints that have the greatest impact on your users and business:

• Authentication.
• Payment processing.
• Product search, etc.

Basically, customers’ priorities should be your priorities. That’s why we also recommend your testing simulate real-world user interactions. You need to make sure your product can perform well in “the wild”, not just a clean, controlled environment.

Finally, keep in mind that API manual test cases aren’t just tech details for engineers. They should align with your business goals. So, pay attention to UX, performance, revenue-generating workflows, etc.

Prepare Manual API Testing Tools & Infrastructure

Choose your tools based on their features and team fit, not popularity. Before settling on a particular option, ask yourself this:

• Can the tool properly cover your testing needs?
• Is it easy to set up, scale, and maintain?
• Does it integrate with your workflows and processes?
• Can your team work with it right away, or will they have to learn it? If it’s the latter, what’s the tool’s learning curve?

If you’re using open-source software, you should also consider whether it has an active community. This will help with troubleshooting and support. Pay attention to the tool’s reporting capabilities, too. You’ll find it easier to track performance, spot issues, and debug with good documentation. Sharing data and insight with stakeholders will be simpler as well. And decision-making will be more informed and targeted.

Don’t forget to take good care of the environment. APIs in manual testing love realistic, consistent spaces. So, be sure to isolate and update them.

Select & Allocate Your Resources

Consider what specialists and how many you’ll need. But do focus on quality over quantity — your team’s skills are everything. And given that API testing in manual testing can be time-consuming, good expertise can advance your project and speed up QA.

Be mindful of the budget. You can always begin with covering critical areas first and branch out to the rest as needed\feasible. Meanwhile, you can put exploratory or ad-hoc testing on hold. But do come back to them if possible. They offer extra values that can boost your product.

If you find it hard to balance money with hiring, tools, and infrastructure, consider external API testing services. QA outsource helps you get quick access to skilled engineers, software, and hardware. And, of course, cost-effectiveness is a given.

Lastly, encourage cross-functional collaboration between developers, product managers, and business teams. It’ll help ensure that testing reflects real-world usage and business needs. Plus, insight and perspective sharing can open up new opportunities for your product.

Detail Expected Outcomes & Metrics

Track defect detection rates to keep up with manual API testing’s progress. Remember that metrics can show your strategy’s effectiveness. But they can also pinpoint issues in development.

• A high defect rate can mean poor code quality.
• It can also signify that you’re over-testing.
• And the same can mean that test rounds miss issues. That’s why they pop up everywhere at once.

You need to pay attention to your test coverage, too. Briefly, you need to keep up with what you’ve planned and what’s being done. That’s why we recommend systematic reviews so that troubles don’t snowball.

Also, don’t forget that API testing’s manual test cases shouldn’t handle functionality exclusively. Performance and security should be on your list of priorities. Though you might need separate specialists for that as well as extra time, it’s something you can’t afford to overlook.

How to Test APIs Manually: Methodologies & Approaches

Now, let’s get to the tech side of your testing. Here, we’ll discuss how you should work with your APIs and what exactly you should check. Keep in mind that this is not an exhaustive list. Many details depend on your project, requirements, and team. Still, the points mentioned are the ones you really shouldn’t miss.

Core Testing Techniques

Start with the fundamentals. Make sure your APIs behave correctly under different conditions.

• Ensure the API performs according to business and technical requirements.
• Confirm the API correctly processes inputs and produces expected outputs.
• Simulates failures to ensure the API responds appropriately.
• Test unusual or extreme conditions to identify potential weaknesses.
• Evaluate how the API handles authentication sessions and token expiration.
• Ensure API responses adhere to expected data formats.
• Test how the API enforces rate limits and handles excessive requests.

Verification Points

Check the details as well. Focus on working with critical elements that dictate API behavior.

• Ensure that requests and responses follow the correct format.
• Verify that data retrieved or modified via the API remains consistent and correct.
• Confirm that the API returns the appropriate HTTP status codes for various scenarios.
• Validate required headers, content types, encoding, and token authentication.
• Confirm that versioned endpoints function correctly and older versions remain supported.
• Ensure that third-party or internal service dependencies are correctly integrated.
• Verify that errors are logged properly and detailed information is available.

Performance & Security Checks

Be sure to validate non-functional aspects. They have one of the biggest impacts on UX.

• Evaluate the time taken for the API to process and return responses under various loads.
• Assess how the API performs when multiple requests are sent simultaneously.
• Ensure that sensitive data transmitted through the API is encrypted using industry standards.
• Test authorization mechanisms.
• Ensure that user sessions expire appropriately and prevent unauthorized access.
• Test against API misuse scenarios.

Quality Assurance Criteria

Finally, move on to high-level checks. These will tell you how effective your manual API testing is overall and whether you’re production-ready.

• Check adherence to OpenAPI, REST, GraphQL, or other relevant API standards.
• Ensure the API behaves the same across development, testing, staging, and production.
• Verify that updates to the API do not break existing integrations or clients.
• Assess how well the API handles increased load and whether it can scale effectively.
• Confirm that API documentation is up-to-date and correctly describes all available info.
• Examine API usability from a developer’s perspective.

Keep in mind that the key to productive testing, and decision-making… and knowledge sharing… Well, a lot of things. The key is structured test case writing. And that’s the focus of the next part.

How to Write Manual Test Cases for API Testing

We’ll skip the basics of test case writing. This you can read up in our blog, including the basics — API testing introduction. There’s nothing fundamentally different you should worry about. But there are some details that might need your attention.

API test cases rely heavily on requests and responses. This means that your test cases should:

• Include a clear input-output structure.
• Be parameterized, letting you check multiple variations (e.g., different user roles and data inputs).
• Cover edge cases (like missing headers or malformed payloads).

APIs interact with multiple systems. So don’t overlook negative test cases, and make sure failure handling is polished.

• Every test should verify both status codes and error messages.
• Check whether error messages are meaningful (not just “Something went wrong”).

Many APIs follow the stateless principle, meaning each request is independent (it doesn’t “remember” past interactions).

• Test cases must be self-contained. They shouldn’t rely on the outcome of previous tests.
• If a test creates data (e.g., adding a user), another test must clean up the data to avoid clutter.
• For stateful APIs, test cases must handle session tokens and multi-step workflows.

In manual API testing, validation is technical. It ensures the backend logic and data handling are correct. Hence, your tests should ensure:

• Correct HTTP status codes (200 OK, 400 Bad Request, etc.).
• Response payload structure (JSON fields, XML elements).
• Data integrity (values match expectations).
• Headers (CORS, authentication, caching directives).

You can use schema validation to check the overall structure against a predefined schema.

Given that APIs don’t change frequently, and there are many of them, you want to plan for potential automation:

• Use variables instead of hardcoded values.
• Support parameterization (testing different inputs easily).
• Avoid dependencies between tests.

You can also hire a general QA engineer for the above. That’s a specialist proficient in both manual testing services and automated testing. They can handle manual QA for as long as you need. And if you decide to automate, they can quickly switch.

Practical Considerations for Manual API Testing

At last, we need to talk about your long game. In any project, you need to plan for the future and long-term success. And every decision you make shouldn’t focus on momentary achievements or goals. So, here are some strategic tips from our team.

Avoid overwork or under-resourcing and attain better deadline management by:

• Ensuring sufficient time and team members are available to cover the full testing cycle.
• Reviewing whether the time and resources spent on manual testing will save more in the long run.
• Considering outsourcing if you need specialized skills or work under tight timelines.
• Exploring the possibility of using automation testing services.
• Investing in tools and training for long-term efficiency.

Reduce manual errors and ensure faster, more accurate test execution by:

• Balancing cost and functionality when choosing between open-source and commercial tools, considering support and scalability.
• Making sure your tools integrate with other systems.
• Picking API manual testing tools that can scale with your needs and adapt to future requirements.
• Accounting for ongoing maintenance, updates, and training when evaluating the total cost of testing tools.

Secure reliable results, productive testing, and refined product quality by:

• Ensuring your team understands API structure, protocols, and data formats to perform thorough testing.
• Investing in continuous training and certifications to keep the team up-to-date with best practices and tools.
• Encouraging engineers to work closely with developers and product managers to create relevant test cases.
• Attracting and retaining skilled specialists by offering growth opportunities and fostering a positive team culture.

Prevent testing delays, cost overruns, and product failures by:

• Taking a proactive approach by testing edge cases and potential failure points.
• Having contingency plans in place to ensure quick recovery.
• Learning the legal implications of testing and having insurance or SLAs to protect yourself.
• Ensuring thorough testing to maintain API quality and safeguard your company’s reputation.

And yes. We’re completely aware that all of the above practices are a lot. But you don’t have to use each point to start getting good results. Stick with what you think is more important for your project. Or see what you can handle better. And if you need help — our team is here to share our expertise and assist your project.

To Sum Up

So, can API testing be done manually? Yes. Should it be done manually? Big yes. Should you automate it? Another big yes. APIs are a handful. That’s why teams automate their checks so often. But that’s also why they can benefit from manual QA the most. It can reveal tiny mishaps or introduce small improvements. And with software development of today, details matter most — they’re what transform good products into remarkable ones.

Manual software testing shouldn’t be viewed as a “cheaper alternative” or automation’s stepping stone. It’s always an opportunity. An opportunity to make something greater.