How to Test Any API Without Documentation with Liudas Jankauskas • TestGuild

About This Episode:

Most API testing stops at the happy path. The problem is that the bugs that actually hurt you in production are sitting in everything many testers skip, like the boundary values, the oversized payloads, the missing tokens, the security headers, the inputs that make no sense at all.

In this episode, Joe sits down with Liudas Jankauskas, who has spent almost twenty years breaking software and testing APIs since 2008.

Liudas demonstrates Rentgen, his free and open-source API testing tool, live on screen. You’ll watch him take a single request from a real app, map it in seconds, and generate dozens of tests covering security, boundaries, performance, and load—all from one click.

You’ll learn:

How to discover APIs hiding under the hood of any application, even when there is zero documentation
Why happy path testing leaves you exposed
How to run a fast hygiene check before your real automation ever starts

Liudas also explains why Rentgen runs completely locally with no server and no data leaving your machine, making it safe for banking, healthcare, and other regulated environments.

Plus, he demonstrates the killer Copy Bug Report feature that drops a standards-based ticket straight into Jira or Trello.

In This Episode You’ll Discover

How to find and test undocumented internal APIs using the browser DevTools Network tab
Why happy path-only testing misses the bugs that matter most
How Rentgen turns one request into security, boundary, performance, and load tests automatically
Where Rentgen fits in your workflow as a pre-automation hygiene layer—not a Postman replacement
How to use it for regression by comparing results across environments
The one piece of advice Liudas gives every tester to level up their API testing

Try Rentgen, free and open source, at Rentgen.io.

Connect with Liudas Jankauskas on LinkedIn:
https://www.linkedin.com/in/liudas-jankauskas/

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About Liudas Jankauskas

Liudas Jankauskas has been breaking software for a living for nearly twenty years. He focuses on API behavior, the boring bugs nobody wants to chase, and the kind of problems that cost real money when they slip into production. He is the creator of Rentgen, a free and open source API testing tool that runs entirely on your machine and finds problems before automation and CI ever touch them.

Connect with Liudas Jankauskas

- Company: rentgen.io
- Blog: www.qaontime
- LinkedIn: www.liudas-jankauskas

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