Kerno

Tests your backend's critical flows locally, so bugs get caught before code merges

Visit KernoFree plan + paid plans · from $30 / dev / monthsource: kerno.io

Kerno is a tool that checks backend code changes while the app is actually running. The pages call it "The AI Backend Runtime QA Engineer." The site is run by FYCK Limited. It's built for developers, and for the coding agents that write code for them.

Kerno writes and runs tests for your critical user flows and the entry points behind them. It runs them locally against your real stack. It connects to coding agents such as Claude Code, Codex, Cursor and GitHub Copilot over MCP. You can also give it your own standards and business rules in plain English. To start, you install the CLI, sign in, and begin checking changes. The pages say there's a free plan that needs no credit card.

What it does

Tests whole user journeys across your APIs, from first request to final resultsource: kerno.io
Checks for security problems, including the OWASP Top 10 and SSRFsource: kerno.io
Tests MCP servers, including each tool's output and error handlingsource: kerno.io
Updates tests as your product changessource: kerno.io
Lets you set your own rules in plain Englishsource: kerno.io
Works with many languages, databases and cloudssource: kerno.io

Our take (opinion)

Best for

💻 Developers who use coding agents and want their changes checked while the app runs
👥 Engineering teams that want fewer bugs found after merge
🌱 Solo developers, open source projects and early startups, since the pages list a free plan and discounts