quality-engineering-visual-baseline
Captures, masks, compares, and updates screenshot baselines for web and mobile suites, with per-region thresholds and a reviewed-diff rule for every baseline change. Use when a screenshot assertion fails, a baseline needs updating, or visual checks are being added; not for deciding what to verify.
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Static analysis is a first line of defense, not a guarantee. Read the source
SKILL.md
Quality Engineering: Visual Baseline
Priority: P1 (HIGH)
Capture
- One baseline per scenario, viewport, theme, and locale that the plan names; never one baseline per developer machine. Capture in the CI image only; a locally captured baseline is a draft.
- Freeze animations and the clock before capture; wait for network idle and fonts loaded.
- Name baselines
<screen>-<state>-<viewport>[-dark][-<locale>].pngnext to the spec in the tool's snapshot folder.
Mask, Then Threshold
- Mask every dynamic region before comparing: clocks, counters, avatars, ads, maps, third-party embeds, randomised ids. A masked region is compared as a solid block, so a layout shift inside it still fails.
- Thresholds are per region and small: text and controls
0.1%max diff pixels, images and charts1%. A suite-wide threshold above1%is a disabled check. - Full detail in Masking and Thresholds.
Classify a Failure
A screenshot diff is VISUAL_DIFF. It is REAL_REGRESSION unless the whole diff lies inside a region that should have been masked or thresholded (then fix the mask, not the baseline). Layout shift, missing element, wrong color, or clipped text is a product change until the product owner says otherwise.
Update a Baseline
- A baseline changes only through a reviewed diff: before and after images in the PR, the intended product change linked, and an approver named in the commit. See Baseline Update Review.
- Never blind
--update-snapshots: it approves every diff in the run, including the regression you have not seen yet. - Update only the baselines whose diff was reviewed, scoped with
--grepand the spec path; regenerate the rest from the same commit so unrelated drift stays visible.
Red Flags
"just update the snapshots" · "bump the threshold to 5%" · "mask the whole header" · "it looks the same to me" — each accepts a regression sight unseen. Stop; review the diff image, name the intended change, then update the one baseline.
Anti-Patterns
- No blind snapshot update:
--update-snapshotswithout a reviewed diff approves an unreviewed visual regression. - No threshold inflation: raising the threshold to make a diff pass disables the check for every future diff.
- No mask as fix: masking the region that regressed hides the regression; mask only genuinely dynamic content.
- No local baselines: a baseline captured outside the CI image fails on the next runner.
References
Files
5- SKILL.md
52c3ed0b3b3.3 KB - evals/evals.json
60a59551e13.0 KB - references/baseline-update-review.md
2da9f2035b1.4 KB - references/masking-and-thresholds.md
e23b00024b1.8 KB - references/tool-matrix.md
c8793022291.6 KB
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