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To test multiple URLs with BackstopJS, add one object per page or page state to the top-level scenarios array. Give each scenario a unique label and its own url; use referenceUrl when the baseline should come from a different environment, such as production while the test capture comes from staging.
Example: configure several pages and viewports
Save this JSON as backstop.json in your project directory. Replace the example hostnames and paths with your own. The configuration fields follow the BackstopJS README; this example has not been run in a project.
{
"id": "site-visual-checks",
"viewports": [
{ "label": "desktop", "width": 1440, "height": 900 },
{ "label": "mobile", "width": 390, "height": 844 }
],
"scenarioDefaults": {
"selectors": ["document"],
"misMatchThreshold": 0.1,
"requireSameDimensions": true
},
"scenarios": [
{
"label": "home",
"url": "https://staging.example.com/",
"referenceUrl": "https://www.example.com/"
},
{
"label": "pricing",
"url": "https://staging.example.com/pricing",
"referenceUrl": "https://www.example.com/pricing"
},
{
"label": "contact",
"url": "https://staging.example.com/contact",
"referenceUrl": "https://www.example.com/contact"
}
],
"paths": {
"bitmaps_reference": "backstop_data/bitmaps_reference",
"bitmaps_test": "backstop_data/bitmaps_test",
"engine_scripts": "backstop_data/engine_scripts",
"html_report": "backstop_data/html_report",
"ci_report": "backstop_data/ci_report"
},
"report": ["browser"]
}Each scenario is one page/state case. BackstopJS describes url as the endpoint or document to test. A list of URLs does not belong inside one url string: create another scenario object for each additional page or distinct state.
How to set shared defaults and per-page behavior
scenarioDefaults is for scenario settings that genuinely apply to every entry. Scenario-level values override shared defaults, so a page that needs different capture behavior can specify its own option without duplicating the common configuration. An explicit empty array such as "selectors": [] overrides a non-empty default and leaves the scenario with no selectors.
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The example uses selectors, misMatchThreshold, and requireSameDimensions as shared settings. Treat the threshold value as an example, not a universal acceptance rule: tune visual comparison to the noise and change tolerance in your own pages.
URLs, baselines, and page selection
url is used for the test capture. referenceUrl is optional; when present, backstop reference uses it to create the baseline, otherwise the reference capture uses url. This lets you compare, for example, the staging test page with the production page at the same route. Confirm the reference endpoint is the environment you intend to keep as the baseline.
Use a distinct, meaningful label for every scenario. Labels help identify the case in reports and saved screenshot names. To rerun only matching labels, the documented CLI supports --filter.
Capture scope and viewport coverage
At least one viewport is required; you can configure multiple sizes, and BackstopJS captures each scenario at each configured viewport. In selectors, the special value document targets the whole document, while viewport targets only the visible viewport. Other selectors can target specific elements.
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More viewports and scenarios mean more captures and a longer run. Choose sizes that represent the layouts you need to protect rather than multiplying viewport cases without a testing need.
Run the baseline and comparison workflow
-
Install and configure BackstopJS for your project, then save
backstop.jsonin the project directory. A JavaScript config is also supported when comments or generated configuration are useful. -
Run
backstop referenceto capture baseline images. This creates references; it does not compare them. -
Run
backstop testto capture the current pages and compare them with the references. Review the report for detected visual differences.Quick wins for a faster PC:
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After inspecting the differences, run
backstop approveonly if the changed screenshots are intentional. Approval promotes the recent test captures to the references used in later comparisons.
For another configuration file, the README documents --config. Check the spelling and supported options against the BackstopJS release installed in your project, especially if an older version or wrapper is involved.
Troubleshooting multiple-URL configurations
-
Only one page is captured: Check that every page has its own object in the top-level
scenariosarray. Multiple page addresses in a singleurlvalue are not separate cases. -
Images or reports are difficult to identify: Make every scenario
labelunique and descriptive; avoid reusing a label for different pages.Do these 3 things before closing this tab:
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-
The baseline shows the wrong environment: Check each
referenceUrl. When supplied, it controls the reference capture; when absent, BackstopJS uses that scenario’surl. -
A scenario captures no elements: Check whether it overrides default selectors with
"selectors": []. An empty array takes precedence over selectors inscenarioDefaults. -
Comparisons are noisy or too permissive: Adjust mismatch and capture settings for the page and acceptance criteria. The documentation defines the threshold option but does not prescribe one threshold for all sites.
-
An engine option is rejected or behaves differently: BackstopJS documentation lists Puppeteer and Playwright engine options, but engine support and behavior can depend on the installed version. Confirm against the version locked in the project; a Playwright fixture in the documentation is pinned to BackstopJS 6.3.25 and does not establish what the latest release supports.
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Frequently Asked Questions
Can one BackstopJS scenario test several URLs?
No. Configure one scenario object for each URL or page state.
Does `backstop reference` compare screenshots?
No. It captures baseline images; `backstop test` performs the comparison.
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