visual-regression-storybook-review

Visual Regression (Storybook) Review

Purpose

Storybook can run three different kinds of automated checks -- the generic test-runner, hosted Chromatic visual/interaction diffing, and the a11y addon's axe-core accessibility checks -- and teams frequently conflate them or wire only one when they need two. This skill reviews which checks are actually wired, whether they gate merge or are advisory-only, and whether visually-critical components and all theme variants are in scope, grounded in current, version-specific Storybook API behavior rather than remembered config shapes that may be stale across majors.

When to use

Use this skill when the user asks to:

• review or configure Storybook's test-runner, Chromatic, or a11y addon setup,
• diagnose why a visual or accessibility regression shipped despite Storybook tests passing,
• decide whether a check should run locally, in the test-runner, or via Chromatic,
• audit whether dark mode/RTL/reduced-motion story variants have visual and a11y coverage.

Context7 Documentation Protocol

Storybook's addon config shape (preVisit/postVisit hooks, parameters.a11y.*, chromatic.config.json fields) has changed across Storybook 8/9/10 and is documented, not folklore -- never assert a hook signature, parameter name, or default value from memory.

1. Call ToolSearch with query "context7" (or "select:mcp__Context7__resolve-library-id,mcp__Context7__query-docs") to load the Context7 tools if not already loaded in this session.
2. Call mcp__Context7__resolve-library-id with library name Storybook to obtain the current Context7-compatible ID (/storybookjs/storybook); prefer the resolved ID over guessing.
3. Call mcp__Context7__query-docs for the specific claim in question -- e.g. "test-runner preVisit postVisit hooks configuration", "a11y addon parameters.a11y.test values", "Chromatic config.json fields and CI wiring" -- before stating it as fact. Do this per review, not once from a prior session's memory.
4. Prefer the official docs URLs in official_docs for primary normative statements (exact parameter names, exact config shape); use Context7 to ground and cross-check the claim before writing it into a finding.
5. If Context7 is unavailable or returns no relevant match, fall back to the official_docs URLs and mark the claim documentation-based (Context7 unavailable) rather than presenting it as freshly verified.
6. Never invent a config key, addon parameter, hook name, or axe-core rule ID that no queried source confirms.

Lean operating rules

• Distinguish the three tools explicitly: test-runner (generic CI test harness, runs locally or in CI via Playwright-driven preVisit/postVisit hooks), Chromatic (hosted visual + interaction diffing with a reviewer UI and git-provider sync), and the a11y addon (axe-core checks configured through parameters.a11y.*) -- do not treat them as interchangeable or assume one subsumes the others.
• Confirm whether parameters.a11y.test is set to 'error' (fails the build on violations) rather than left unset or at 'todo' (warns only) before crediting a project with enforced accessibility gating; 'off' disables the check entirely except for manual panel review.
• Require that visually-critical stories include dark mode, RTL, and prefers-reduced-motion variants in the checked set, not just the default light theme -- a diff/a11y suite that only ever renders the default theme systematically misses regressions in every other supported mode.
• Verify the exact addon/config API shape (e.g., preVisit/postVisit hook signatures, injectAxe/configureAxe/checkA11y from axe-playwright, or parameters.a11y.context/config/options) against the installed Storybook major version before recommending a .storybook/test-runner.ts or preview.ts diff, since these shapes have changed across Storybook 8/9/10.
• Recommend masking or mocking non-deterministic content (timestamps, animations, randomized data, live network responses) before recommending a looser pixel-diff tolerance -- widening tolerance first hides the actual source of visual noise rather than fixing it.
• Treat the test-runner and Chromatic as complementary, not redundant: the test-runner can run custom assertions locally and in any CI, while Chromatic adds hosted visual/interaction diffing with reviewer approval and git sync; a project that has only one may still have a real coverage gap depending on what it needs.
• Load the design-token-governance skill instead of this one when the root cause is a token/contrast issue rather than a Storybook wiring gap; load wcag-22-accessibility-audit when the question is about accessibility compliance strategy broader than what the a11y addon checks.

References

Load these only when needed:

• Test-runner and Chromatic wiring -- use when reviewing or configuring the test-runner's preVisit/postVisit hooks, CI invocation, or Chromatic project setup and the distinction between the two.
• Accessibility addon gating -- use when reviewing or configuring the a11y addon's parameters.a11y.test gating behavior, axe-core rule configuration, or diagnosing why violations aren't failing CI.
• Theme and variant coverage -- use when auditing whether dark mode, RTL, and reduced-motion story variants have visual/a11y coverage, or when non-deterministic content needs masking before diffing.

Response minimum

Return, at minimum:

• which of the three tools (test-runner/Chromatic/a11y addon) is in scope and whether it currently gates merge,
• theme/variant coverage gap (dark mode, RTL, reduced-motion) if any,
• evidence level and the Storybook major version the guidance targets,
• proposed config diff (not applied),
• security caveat on any Chromatic/Percy token or PII-bearing baseline reviewed.