Introduction of Satatus code 4xx and 500.
API automation test cases gives the HTTP status code 400 more often. In this post I will explain what are the scenarios we get HTTP status code 4xx .
HTTP 400 series status codes are Client Error responses. Meaning the request sent by the Client (Website/Mobile App from any devices) is not valid or cannot be processed, even though the Server(Database/Files/webservers) is reachable.
Http status code 500 indicates that the server encountered an unexpected condition that prevented it from fulfilling the request.
HTTP Status 400 -Bad Request
When Invalid format is passed in JSON in request we get Error code 400.
Common Reasons :
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Missing required fields
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Invalid JSON(Missing Commas, Double quotes or Brackets, etc
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Wrong data type-Sending string instead of Number, Sending Null instead of Required type.
HTTP Status 401 – Unauthorized
401 code means Authentication is required or token is invalid.
Common Reasons :
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Token is missing – When user forgets or miss to give the token is Authorization we get 401 in the Response
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Token is expired – When the user is unaware that the token got expired and uses the same token he gets 401 code
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Wrong credentials-When extra quotation or trim happened by mistake
HTTP Status 403 – Forbidden
403 code means you are authenticated, but not allowed to access the resource.
For a user who is allowed to use the system/application but when he tries to use a restricted page or functions like Delete then 403 code will be thrown
HTTP Status 404 – Not Found
Meaning the requested resource does not exist.
When the wrong URL or non-existing id is used in the request we get 404 user Not found
HTTP Status 500 – Internal Server Error
Client sends valid request but the Server crashed or failed while Processing .
Common causes of Error code 500 :
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Database connection failures
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Incorrect server configuration
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Timeout while processing a request
Common causes of Error code 500 :
1.Improper Server configuration.
2.out-of-memory (OOM) issues.
3.Unhandled exceptions.
4.Improper file permissions,
Hope you find this post useful and you can guide your API developers to implement them and make it industry standards compliant.
Sinduja works as Director of Quality Assurance at Knowillence, responsible for ensuring software quality across diverse IT projects. She focuses on building robust testing processes, identifying risks early, and enabling reliable, scalable releases. With a keen eye for detail and a process-driven approach, she helps project teams deliver stable, high-quality solutions. Her work plays a key role in strengthening execution discipline and customer confidence.