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1Scan for outdated or missing drivers - takes under a minute2Repair Windows errors before they cause bigger problems3Fix the driver behind crashes, sound loss and screen glitchesTo test multiple pages 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 than the page being tested.
Configure one BackstopJS scenario per URL
BackstopJS does not take a list of URLs in one scenario’s url field. Instead, each scenario describes one page or state to capture. A scenario’s url is the page used for the test capture; its optional referenceUrl can point to the corresponding page in the baseline environment.
This JSON-style example covers three pages at desktop and mobile sizes. Replace the example hostnames and paths with URLs that your capture environment can reach.
{
"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 viewport is applied across the scenarios, so this configuration requests captures for each of the three pages at both sizes. The example illustrates the documented configuration fields; it has not been run in a project. The misMatchThreshold value is an example, not a universal recommendation.
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Choose what each scenario captures
Required per-scenario values
Give every scenario a unique, meaningful label and a url. Labels identify cases in saved image names and help you filter runs. For pages with different states—such as a modal open or a logged-in view—create separate scenarios when each state needs its own capture.
Reference and test environments
If you want to compare staging against production, set each scenario’s url to its staging page and its referenceUrl to the matching production page. backstop reference uses referenceUrl when it is present; otherwise, it uses url. Check the mapping carefully so each test page is compared with the intended baseline.
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Shared defaults and page-specific overrides
Put settings that genuinely apply to every scenario in scenarioDefaults. Scenario-level values override the corresponding defaults, which lets one page use different capture settings without duplicating the common configuration. An explicit empty array, such as "selectors": [], overrides a non-empty default and leaves that scenario with no selectors.
Selectors, viewports, and comparison settings
- At least one viewport is required. Define more than one when you need coverage at different screen sizes; every additional viewport increases the amount of capture work.
- The special selector
documenttargets the whole document, whileviewporttargets only the visible viewport. Selectors can also target specific elements. - Scenario options include readiness conditions, delays, selectors, mismatch threshold, and dimension matching. Use page-level overrides when a page needs different behavior.
- Choose a mismatch threshold to fit the project’s visual noise and acceptance needs. The configuration documentation defines the option but does not prescribe one threshold for all sites.
Save and run the multiple-URL configuration
- Save the JSON as
backstop.jsonin the project directory. BackstopJS also supports a JavaScript configuration when you need comments or generated configuration. - Run
backstop referenceto capture the baseline images. This command creates references; it does not compare them with current captures. - Run
backstop testto capture the current pages and compare them with the saved references. Review the resulting browser report for detected visual differences. - After reviewing the changes, run
backstop approveonly if the new screenshots are intended to become the baseline. Approval promotes the recent test captures to reference images.
For a larger scenario list, the documented --filter option can limit execution to matching scenario labels. If you use --config to select a non-default configuration file, check the spelling against the BackstopJS release installed in your project, especially when using an older release or wrapper.
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Common configuration mistakes and fixes
- Several URLs placed in one
urlvalue: create a separate scenario object for every page or state. A scenario represents one capture target. - Duplicate labels: rename scenarios so each label is distinct and the resulting images are identifiable.
- Unexpected baseline captures: check whether
referenceUrlis set. The reference command uses it in preference tourl. - No selectors captured for one page: inspect that scenario for
selectors: []. An explicit empty array overrides a non-emptyscenarioDefaults.selectors. - Comparisons are noisy or too permissive: tune comparison settings to the pages and acceptance criteria in your project; do not treat the example threshold as a standard.
- Wrong or unsupported browser engine behavior: confirm engine options and support against the version locked in your project. BackstopJS documentation lists Puppeteer and Playwright options, and a fixture for version 6.3.25 demonstrates a Playwright configuration; that historical fixture does not establish current latest-version support.
- Approved changes cause later comparisons to shift: approval replaces the reference baseline with recent test captures. Review the report before approving, and rerun from the intended baseline if an unintended approval was made.
Run-time, reliability, and cost considerations
The number of captures grows with the number of scenarios and viewports: three scenarios at two viewports mean six page-and-viewport combinations. Add only viewport sizes and page states that matter to your coverage, and use --filter for focused runs where appropriate.
Keep URLs reachable from the environment where BackstopJS runs, and make reference-to-test URL pairs correspond page by page. The documented workflow depends on saved reference images: establish the baseline first, compare subsequent captures, and approve only intentional visual changes. No universal comparison threshold or run-time figure is established for all projects.
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Or skip the browser setup
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One GET request returns an image or PDF. For example, this cURL command saves a WebP capture of the homepage:
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