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ScreenshotAPI’s POST /v1/compare endpoint compares a freshly rendered page with either a second URL or a saved, named baseline. It returns a changed-pixel percentage, boxes around changed regions, and a diff image. Use the result to find visual changes—not as automatic proof that a page is broken.
Choose what to compare
The endpoint offers two reference modes. Send exactly one: against for a second URL to render now, or baseline for a saved image identified by name. Do not send both.
| Mode | Best for | What is rendered |
|---|---|---|
against |
Comparing two current pages, such as a preview deployment and production | Both URLs are rendered for the comparison |
baseline |
Checking one page over time in visual regression tests | The current URL is rendered and compared with the stored image |
ScreenshotAPI says the same capture parameters apply to both sides, helping the images line up. Keep viewport dimensions and any other relevant capture settings consistent between runs so differences are less likely to come from mismatched capture conditions.
Read the comparison result
The documented response includes three useful forms of evidence:
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- Changed-pixel percentage: a compact measure of how much of the image differs.
- Changed-region boxes: locations of detected changes, useful for narrowing review.
- Diff image: changed areas are tinted and unchanged areas are faded.
These outputs identify visual differences, not their cause or importance. A changed pixel may reflect an intended design update or a rendering variation; the documentation does not establish a universal acceptable threshold. Have a person or project-specific review process decide whether the change is expected.
Run a comparison with the API
Call POST /v1/compare with the current page and one reference mode. Use the authentication and request format specified in ScreenshotAPI’s comparison documentation; the endpoint is documented there alongside its parameters and response. The supplied documentation does not establish a stable response schema or a specific authentication header here, so avoid hard-coding assumptions about response field names without checking the current endpoint reference.
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Compare two URLs now
Use against when both pages should be rendered at comparison time, for example a preview URL against the production URL. Keep the viewport and other capture parameters fixed for a meaningful side-by-side comparison.
Compare against a saved baseline
Use baseline with the baseline name to compare one current render with a previously saved image. For repeated CI checks, store the baseline persistently; ScreenshotAPI’s integration guide advises keeping baseline images with the repository because CI artifacts can be temporary.
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The endpoint documents update_baseline, which defaults to false. Set it when an observed change is intentional and should become the new reference. Avoid updating the baseline automatically on every run: doing so can replace a useful reference with an unreviewed regression.
Build a visual-regression check into CI
- Store the API key as a CI secret. Do not hard-code it in a pipeline file or commit it with the code.
- Capture the preview or staging page. Use the intended viewport and capture settings for the test.
- Compare with a persistent baseline. Use the named-baseline mode and ensure the baseline survives between pipeline runs.
- Make the result actionable. Report the percentage, changed-region boxes, and diff image. Use a threshold selected for your project, or require review; ScreenshotAPI does not prescribe a universally correct threshold.
- Accept expected changes deliberately. Review the diff first, then update the named baseline when the change is approved.
ScreenshotAPI names GitHub Actions, GitLab CI, and Bitbucket Pipelines as integration targets, and says the API can be called from CI/CD with curl or a script. Follow your platform’s secret-management and artifact-retention practices to keep credentials private and comparison images available for review.
Account for quota and hosted-rendering limits
Each rendered side consumes one quota unit; the comparison operation itself is free. A URL-to-URL comparison therefore uses two renders, while a comparison against an existing baseline renders the current page. Failed renders receive their reserved unit back. The documentation’s current plan table lists monthly quotas of 100 renders on Free, 2,000 on Starter, 10,000 on Pro, 25,000 on Team, and 100,000 on Business, resetting at the start of each UTC calendar month. These are changeable plan figures, so confirm the current table before estimating usage.
The hosted renderer rejects some destinations and URL forms. In particular, the docs list schemes other than HTTP/HTTPS, loopback, RFC1918, link-local, carrier-grade NAT and cloud metadata addresses, hostnames resolving to those ranges, embedded URL credentials, and ports other than 80, 443, 8080, and 8443. A staging page available only on a private network may therefore be unreachable under the service’s rules.
Troubleshoot common comparison failures
- The request is rejected for its reference parameters: provide one of
againstorbaseline, not both, and check the current endpoint docs for required fields and request formatting. - The hosted service cannot reach staging: check the scheme, resolved destination address, embedded credentials, and port against the documented URL restrictions. A private-only destination may not be capturable through the hosted endpoint.
- The diff shows widespread changes: verify that both sides use the same viewport and capture parameters, and inspect whether the page content itself changed. The endpoint’s matching-parameter behavior helps align captures, but it cannot make distinct pages or states identical.
- The build fails on a small percentage change: review the diff and changed-region boxes, then adjust the project’s threshold or add a human review step. No universal threshold is documented.
- A baseline comparison has no useful persistent reference: confirm that the named baseline was saved and remains available across CI runs; do not depend on temporary CI artifacts as the sole copy.
- Quota estimates are higher than expected: count each rendered page, not each comparison operation. A two-URL comparison renders two sides.
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ScreenshotNeo can return a screenshot with one GET request, without setting up a browser capture script. Its clean-shot workflow accepts cookie or consent banners and removes more than 60 known consent platforms, newsletter popups, and chat widgets before capture; each step can be turned off. Bot checks, blank pages, timeouts, failed loads, and cache hits cost nothing, with response headers identifying the page verdict and billing status. Its MCP server provides screenshot tools for AI agents, and the free plan includes 1,000 screenshots a month with no card; paid plans start at $5 for 3,000.
Example request (replace YOUR_API_KEY and the target URL):
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webpSee the ScreenshotNeo API documentation for request options. ScreenshotNeo is a screenshot API and MCP server by Yorker Media; learn more at screenshotneo.com. Sign up free for 1,000 screenshots a month, with no card required.
Frequently Asked Questions
Can ScreenshotAPI tell whether a visual change is a bug?
No. The comparison reports image differences; a reviewer or project-specific rule must determine whether a difference is a defect or an expected change.
How often do ScreenshotAPI’s monthly render quotas reset?
The documentation says they reset at the start of each UTC calendar month; check the current plan table because quota figures can change.
Quick Recap
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