Use BackstopJS’s comparison workflow to update references safely: run backstop test, inspect the visual report, then run backstop approve to promote only the reviewed captures. Avoid using backstop reference for routine updates: it creates references without comparison and deletes existing reference images by default.
Safest workflow: test, review, approve
- Run a comparison. From your project directory, run
backstop test. BackstopJS captures test screenshots and compares them with the existing references, then produces a report. If you only need to capture particular scenarios, use the scenario-label filter supported by your project’s configuration and installed BackstopJS version. - Inspect the report before accepting anything. Compare the reference, test, and difference views. Check that each difference reflects the intended application change—not an incorrect URL or environment, a page captured before it finished loading, or inconsistent rendering.
- Approve only reviewed changes. When the captures are correct, run
backstop approve. Approval promotes images from the most recent test batch to the reference collection; subsequent tests compare against those approved images. - Check the resulting files. Review the changed reference images and keep a recoverable copy of the prior baselines, such as in version control. This is a prudent safeguard, not a documented BackstopJS requirement.
The project README describes approval as the route for accepting a test batch that looks good. It also says that when the test used a custom configuration path, pass that same path when approving.
Approve only a subset of captures
To limit which images are promoted, use the approval filename filter: backstop approve --filter=<image_filename_regex>. Select a pattern that matches only the captures you have reviewed. This filter applies to approval; it is distinct from a scenario-label filter used to limit which scenarios are captured during testing.
If you ran the test with a custom config, continue with that config when approving, for example: backstop approve --config=path/to/backstop.json. Use the actual path and options supported by the BackstopJS version installed in your project.
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Why backstop reference is riskier
backstop reference generates references directly without first running the comparison workflow. The BackstopJS npm documentation says it deletes existing reference images by default before creating new ones. That makes it unsuitable as a casual substitute for reviewing and approving a test batch.
The npm documentation describes --i as an incremental option that avoids first deleting files in the reference directory. Since CLI behavior can vary by installed version, verify the option against your project’s version before relying on it. Incremental generation is not a replacement for checking that the newly generated images are the intended baselines.
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Keep comparisons meaningful
- Keep the environment consistent. The BackstopJS README recommends Docker rendering to help consistency across environments; it does not guarantee identical results in every setup.
- Use the same configuration. Pass the custom config used for the test when continuing to approval.
- Review the page state, not just the diff. Confirm the right URL, viewport, content, and loaded state before accepting visual changes.
- Do not assume a universal pass threshold. The cited workflow documentation does not establish a generally acceptable mismatch percentage; judge each change against the intended UI change.
- Preserve prior baselines. Keep references recoverable and inspect the repository changes after approval, particularly before committing broad updates.
Troubleshooting reference updates
The report shows unexpected differences
Check whether the test used the intended URL, environment, viewport, and page state. A wrong deployment or incomplete load can create misleading differences. Correct the cause and rerun backstop test rather than approving uncertain screenshots.
Approval changed more images than intended
Approval promotes images from the most recent test batch. Use --filter=<image_filename_regex> to restrict approval to matching filenames, then inspect the resulting changes. For future runs, limit test capture with a scenario-label filter when appropriate; capture filters and approval filters operate at different stages.
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The command cannot find the expected configuration
If the preceding test used a custom config path, provide that same path to the approval command. Check the path relative to the directory where you run BackstopJS and consult the installed version’s CLI help if its option syntax differs.
Existing references disappeared after generation
The documented default for backstop reference is to delete existing reference images before creating new ones. Restore the prior files from version control or another backup if available. For an intended incremental generation, check whether your installed version supports --i and confirm its behavior before running it.
Rank #4
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Results differ between machines
Use a consistent rendering environment; the README recommends Docker to help with cross-environment consistency. Review captures in the report before approval, since Docker does not promise identical output in every setup.
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If your goal is to capture a current page rather than maintain BackstopJS comparison baselines, ScreenshotNeo can return a screenshot with one GET request. It removes cookie banners, popups, and chat widgets before capture; bot checks, blank pages, and failed loads are never billed; its MCP server lets AI agents take screenshots; and 1,000 screenshots per month are free with no card, with paid plans starting at $5 for 3,000.
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For example, this cURL request saves a WebP screenshot of the target page:
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curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webp
See the ScreenshotNeo API documentation for setup and options. ScreenshotNeo is a screenshot API, not a replacement for BackstopJS’s reference comparison and approval workflow. Sign up for the free plan to get 1,000 screenshots a month with no card.
Quick Recap
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