// Penetration Testing AI guide

API security testing basics

What makes API testing different from web-page testing — understanding the contract, testing authorization on every endpoint, and why broken object-level access is so common.

APIs power most modern applications, and they fail in ways a browser-driven test often misses. Testing them well means thinking about the API's contract directly — the endpoints, the parameters, and above all who is allowed to do what.

Understand the contract first

Find the API's documentation or specification (such as an OpenAPI/Swagger definition) if it exists, and map the endpoints, methods, and expected parameters. If there is no spec, reconstruct one from observed traffic. You are testing the contract, so you need to know what it claims to be.

Authorization is the main event

The most common and impactful API issues are authorization failures. The classic is broken object-level authorization: an endpoint that returns object 123 for you will happily return object 124 belonging to someone else, because it checks that you are logged in but not that the object is yours.

  • Test every endpoint as different roles, including no authentication at all.
  • Change identifiers to reference objects that belong to other users.
  • Check that write and delete operations enforce the same ownership as reads.

Don't forget the basics

Rate limiting, input validation, and information leakage in verbose errors all matter for APIs too. But if you only have time for one thing, test authorization on every endpoint.

Related guides

A web application testing workflowA structured methodology for authorized web application testing — mapping the app, testing by vulnerability class, verifying findings, and documenting results a team can act on.

Terms used here

Penetration testingAn authorized, scoped assessment that simulates real attacks against a system so its owner can find and fix weaknesses first. A legitimate penetration test always has defined scope, rules of engagement, and written permission before any testing begins.VulnerabilityA flaw or weakness in a system that could be exploited to compromise its confidentiality, integrity, or availability. Not every vulnerability is equally serious; severity depends on how easily it can be exploited and what the impact would be.Attack surfaceThe full set of points where an attacker could attempt to interact with a system — every exposed domain, endpoint, service, and input. Mapping the attack surface is a core goal of reconnaissance because you can only assess what you know exists.