How to Test Any API Without Documentation

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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Automation Testing with Joe Colantonio

A podcast interview with Ludis, a 20-year software testing veteran who built Rentgen, a free open-source API testing tool. The conversation covers how to discover undocumented internal APIs using browser DevTools, and how Rentgen automates the tedious parts of API testing — edge cases, boundary tests, security header checks, and basic performance insights — by taking a single API request, mapping its fields, and auto-generating dozens of test cases. The tool is fully local (no cloud calls), complements existing Postman/Playwright automation rather than replacing it, and is intended as a first-pass sanity check before deeper automation begins. CI/CD integration is on the roadmap.

How to Test Any API Without Documentation

<p>One API request can reveal a lot more than most teams expect. That’s the idea behind Rentgen—start with real traffic, then automatically explore everything around it before writing a single test.</p>
