DevTools Assertions - LambdaTest

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DevTools assertions let you verify data that isn’t visible on the page: HTTP network traffic, browser console output, performance metrics, cookies, localStorage, and clipboard. KaneAI captures this data automatically in the background; you just write what to check.

Available Domains

Domain	What It Captures	Documentation
Network	HTTP requests and responses	Status codes, headers, response bodies, timing
Console	Browser console messages	Errors, warnings, log messages, JS exceptions
Performance	Core Web Vitals	LCP, CLS, INP, FCP, TTFB
Cookies	Browser cookies	Names, values, flags (httpOnly, secure, sameSite)
localStorage	Browser localStorage	Key-value pairs stored in the browser
Clipboard	Browser clipboard	Copied text, HTML, image, and formats present

How It Works

Each DevTools domain follows the same pattern:

Capture: KaneAI captures the data automatically during your test run
Generate: When a checkpoint triggers, the AI generates code to query the captured data
Execute: The code runs in an isolated sandbox and returns a result
Assert: The result is compared against your expected value

You don’t write code. You write natural language objectives, and KaneAI handles the rest.

Examples

Assert: no API calls returned 5xx
Assert: no console errors on the page
Assert: page LCP is under 2500ms
Assert: session cookie exists and is httpOnly
Assert: auth_token is stored in localStorage

All Checkpoint Types Work

DevTools assertions support all three checkpoint types:

Assert: “Assert: no console errors”, fails the test if there are errors
Extract: “Store all cookies”, saves the data for later steps
If/Else: “If the API returned 200 then proceed, else retry”, branch on the result

Important Notes

DevTools data is not visible in a screenshot. KaneAI will never try to open the browser DevTools panel
Each domain captures data differently. See individual pages for details on timing and scope
All assertions run in an isolated sandbox. Generated code cannot access the file system or network

⌘I

​Available Domains

​How It Works

​Examples

​All Checkpoint Types Work

​Important Notes

Available Domains

How It Works

Examples

All Checkpoint Types Work

Important Notes