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

# Writing assertions

> How to write **AI check** assertions that pass reliably and fail for the right reasons.

Momentic's AI evaluates assertions against the DOM, accessibility tree, and a
screenshot of the viewport. The same rules from
[Finding elements](/core-concepts/finding-elements) apply, plus a few specific
to assertions.

## Best practices

* **Keep assertions short and specific.** Aim for under 20 words; split compound
  assertions into multiple steps.
* **Provide context.** Point at the relevant region of the page and define any
  non-standard terminology.
* **Remove ambiguity.** The answer should be clearly true or false given the
  page state. When in doubt, use single quotes for exact text matches.

## Good assertions

| Category                        | Example                                                      |
| ------------------------------- | ------------------------------------------------------------ |
| Presence or absence of text     | A congratulations message is shown in the modal              |
| Presence or absence of elements | The page shows 3 search results                              |
| Logical statements              | The publish date of this article is more than 30 days ago    |
| Page state                      | There is no error message present on the page                |
| Color                           | The buy button is blue                                       |
| Layout                          | The 'XL' button is the largest button in the submission form |
| Images and video                | There is a LinkedIn icon on the page                         |

## Bad assertions

| Problem              | Bad                                                                                      | Better                                                |
| -------------------- | ---------------------------------------------------------------------------------------- | ----------------------------------------------------- |
| Malformed            | Search results                                                                           | There are search results displayed on the main body   |
| Ambiguous            | The order of the results is correct                                                      | The search results are sorted by date                 |
| Multiple focuses     | The logo is blue, the page shows 4 results, and the last result is more than 30 days old | Split into 3 separate assertions                      |
| Contains an action   | Wait for the results to appear                                                           | Use a **Wait** step, then assert the results appeared |
| Imperceivable detail | The color of line divider is #ff5733                                                     | The color of the divider looks red                    |
| Subjective           | The page looks well designed                                                             | No text in the table overflows its cell               |
| Time-sensitive       | The video plays a 10-second advertisement                                                | Assert on DOM state instead                           |

## Pre-trained behavior

### Typos

The agent tolerates minor typos. `john@@gmail.com` will match `john@gmail.com`.

For exact matching, wrap the expected value in single quotes and instruct the
agent explicitly:
`the username is exactly 'john@@gmail.com'. do not allow any typos`.

When generating test data programmatically, prefer long, distinct values to
avoid accidental matches.