> ## Documentation Index
> Fetch the complete documentation index at: https://www.testmuai.com/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# DevTools Assertions

> Verify data that is not visible on the page: HTTP network traffic, console output, performance metrics, cookies, localStorage, and clipboard.

***

<Note>
  **Using Claude Code, Cursor, or another coding agent?** Paste this into your prompt to run cross-browser and real-device tests, debug sessions, and wire up CI on the TestMu AI cloud:

  ```
  Read https://www.testmuai.com/support/docs/SKILL.md to set up TestMu AI (formerly LambdaTest) cloud testing.
  ```
</Note>

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](/docs/docs/kane-cli-checkpoint-devtools-network/)           | HTTP requests and responses | Status codes, headers, response bodies, timing    |
| [Console](/docs/docs/kane-cli-checkpoint-devtools-console/)           | Browser console messages    | Errors, warnings, log messages, JS exceptions     |
| [Performance](/docs/docs/kane-cli-checkpoint-devtools-performance/)   | Core Web Vitals             | LCP, CLS, INP, FCP, TTFB                          |
| [Cookies](/docs/docs/kane-cli-checkpoint-devtools-cookies/)           | Browser cookies             | Names, values, flags (httpOnly, secure, sameSite) |
| [localStorage](/docs/docs/kane-cli-checkpoint-devtools-localstorage/) | Browser localStorage        | Key-value pairs stored in the browser             |
| [Clipboard](/docs/docs/kane-cli-checkpoint-devtools-clipboard/)       | Browser clipboard           | Copied text, HTML, image, and formats present     |

## How It Works

Each DevTools domain follows the same pattern:

1. **Capture**: KaneAI captures the data automatically during your test run
2. **Generate**: When a checkpoint triggers, the AI generates code to query the captured data
3. **Execute**: The code runs in an isolated sandbox and returns a result
4. **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