> ## Documentation Index > Fetch the complete documentation index at: https://docs.mobster.dev/llms.txt > Use this file to discover all available pages before exploring further. # Screenshots that must not change > Compare the screen a check ends on to a baseline image in every appearance, text size and language. A SwiftUI view can compile clean and still clip at a larger text size or lose its contrast in the dark appearance. A `snapshot` in a check's `expect` compares the screen the check ends on to a baseline image, with no model. ## Add a snapshot to a check Add these keys to an existing [check file](https://docs.mobster.dev/checks.md#the-check-file): ```yaml theme={"theme":"css-variables"} conditions: appearance: [light, dark] content_size: [large, accessibility-extra-large] expect: - snapshot: settings mask: [{ id: last_synced }] ``` Run the checks: ```sh theme={"theme":"css-variables"} mobster test ``` A missing baseline is recorded and ends `needs_review`. Inspect the image before you commit it. Later runs compare against that baseline. Baselines are PNGs in `.mobster/snapshots//@---.png`, for example `.mobster/snapshots/settings/settings@iphone-17-pro-dark-accessibility-extra-large-default.png`. A condition the check doesn't set reads `default`. `` is the check file's path under `.mobster/checks`, without the suffix. Commit them: they are the expected screens. ## Read a changed snapshot * **No baseline for this device and these conditions.** Mobster saves the screen as the baseline and the check ends `needs_review` with "baseline recorded". It never fails a check for a missing baseline. Look at the PNG, commit it, and the next run compares to it. * **A baseline.** Mobster takes a full-size PNG after the screen settles and compares it to the baseline. * **The same size, within the threshold.** The snapshot passes. * **Over the threshold.** The check fails with class `finding`, the message says how much of the screen changed, and the run folder holds `snapshots/-diff.png`: the screen faded, with the changed pixels red. * **A different size.** The check fails and says both sizes. A baseline belongs to one device, so another device gets its own baseline. * **`--update-snapshots`.** Mobster writes the baseline whatever the screen shows, and the snapshot passes. With `--check NAME` it updates only the checks with that name or file name. Read the diff of the PNGs in your pull request before you commit. Mobster blurs both images by 2 px, then counts a pixel as changed when any color channel differs by more than 24 of 255. Antialiasing and subpixel text rendering stay under that, so they never fail a check. The check fails when more than `threshold` percent of the unmasked pixels changed (default 0.1). Mobster leaves out: * **Your masks.** An `id` or `label` mask covers every shown element it matches. A `rect` is in points. Masked pixels count in neither the changed pixels nor the total. * **The keyboard.** While the keyboard shows, Mobster masks it and the text fields on screen, because a caret blinks. * **The status bar.** On a simulator, Mobster sets 9:41, full battery, full signal and Wi-Fi for the run (a `status_bar` condition of yours wins) and puts it back afterwards. On a real iPhone it can't, so it masks the status bar. A person reads the diff and decides whether a change is a bug. Mobster doesn't compare one baseline across two devices or check contrast ratios. A baseline file names the device but not the iOS version, so update the baselines when you move to a new simulator runtime. ## Accept an intended change After you inspect the diff, update only the check whose screen you meant to change. For a check named `settings`: ```sh theme={"theme":"css-variables"} mobster test --update-snapshots --check settings ``` This replaces its baselines with the screens from this run. Review the PNG changes before you commit them. ## Clean up old baselines `mobster test snapshots` marks each baseline `current`, `stale` (its check still has the snapshot, but not for this appearance, text size or locale) or `orphaned` (no check has that snapshot). Mobster lists them and deletes nothing: remove them with `git rm`. In `results.json`, a result with a snapshot has `snapshot` with `name`, `status` (`matched`, `changed`, `size_changed`, `recorded` or `updated`), `changedPercent`, `thresholdPercent`, `regions` and `masks` as `[x, y, width, height]` in pixels, `size`, `diffMs`, and the absolute paths of the `baseline`, `current` and `diff` images. `junit.xml` lists the same paths in the case's ``, so a CI system can attach the diff. The run's own report shows the three images side by side. This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.