Pattern Documentation

Pattern documentation

A skill for writing documentation for design system patterns. Patterns are distinct from components: a component is a discrete, reusable UI element; a pattern is a recurring solution composed from multiple components that addresses a specific user or product problem. Form validation, empty states, error handling, progressive disclosure — these are patterns.

Before you begin: verify references

Confirm that every path in this skill's frontmatter references: exists relative to this SKILL.md. If any is missing, stop: the install is incomplete, usually because a flattening installer (for example npx skills install) dropped the repo-root knowledge-notes/ directory. Tell the user to reinstall by a method in 1-INSTALL.md and run verify-install.sh from the install root. Proceed without the references only if the user explicitly says to, and then say in the output that it was produced without the pack's reference material.

Context

Pattern documentation is systematically underdone in most design systems. Teams document components in detail and leave patterns as implicit knowledge — accumulated through convention, absorbed during onboarding, and lost when people leave. The result is parallel local solutions that drift apart over time, and product teams that rebuild the same interaction in slightly different ways because no one wrote down the shared answer.

Good pattern documentation does two things. It explains the pattern clearly enough that a designer or developer encountering it for the first time can apply it correctly. And it explains the edges: when this pattern is not the right choice, what alternatives exist, and how to handle the cases that do not fit neatly.

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Step 0: Pattern discovery guide

Before documenting a pattern, confirm it is worth documenting. Not every recurring UI solution is a pattern — some are conventions, some are coincidences, and some are too specific to generalise.

A UI solution is a documentable pattern if:

• It appears in three or more distinct product contexts (not just three instances in the same product), each located in code or Figma and cited by path or URL, or named by the user
• It solves a user-facing problem, not just a layout convenience
• It composes two or more design system components in a specific relationship
• Teams have independently arrived at similar solutions (convergent evolution is the strongest signal)
• Getting it wrong has real consequences (accessibility, usability, consistency)

A UI solution is NOT a documentable pattern if:

• It appears in only one product context (it is a local convention)
• It is a single component used in a standard way (that belongs in the component's usage guidelines)
• It varies so much between instances that no shared structure can be extracted

If the bar isn't met, say which criteria failed and what to write instead: a single component used in a standard way belongs in usage-guidelines; a one-product solution is a local convention note in that product's docs; instances too varied to share a structure need a conversation, not a page. Then stop; don't write a pattern page for something that isn't one.

Where to find undocumented patterns:

1. Look at drift-detection findings classified as E (system gap) — these often reveal patterns teams are building independently
2. Review support channel questions — recurring "how do I..." questions about multi-component interactions signal undocumented patterns
3. Ask product teams: "What do you build most often that is not a single component?" The answers are pattern candidates
4. Review design file reuse — Figma frames that appear across multiple files without being components are likely patterns

Provenance rule. Product contexts, instances, states and accessibility behaviour in the documentation come from code, Figma, the team's docs or the user, and are cited by path or URL where they come from files. If you can't locate instances, ask the user; never invent product or team names. Rules you propose rather than observe are marked "proposed". See "Every figure and fact needs a source" in the output-discipline knowledge note.

Step 1: Establish the pattern scope

Ask for or confirm:

• Pattern name (clear, descriptive, not jargon)
• The user problem or product need this pattern addresses
• Which components from the design system are involved
• Product contexts where this pattern is already in use: search the codebase and Figma for instances first, then ask the user to confirm or add to them
• Any known edge cases or exceptions the documentation should address

If the pattern does not yet have a name, propose one before writing the documentation. Pattern names should describe the interaction or function, not the visual treatment: "confirmation dialog" not "modal with two buttons."

Step 2: Write the pattern documentation

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[Pattern name]

Category: [navigation / forms / feedback / layout / data display / other] Components used: [list the design system components this pattern draws on] Last updated: [date]

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What this pattern does

One to two sentences. Describe the pattern in terms of what it accomplishes for the user, not how it looks or which components it uses.

Example (form validation): Communicates the status of user input during and after form interaction, surfacing specific errors in the context where they occur so users can correct them without losing their progress.

Example (empty state): Guides users when a view has no content to display — whether because data does not exist yet, a search returned no results, or content was removed — and offers a clear path to the next action.

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When to use this pattern

Describe the conditions under which this pattern is the right choice. Be specific about the context. Avoid "use this when you need to show an error" — that is not a usage condition, it is a circular definition.

Good format: "Use this pattern when [user or product situation]. It is appropriate when [specific conditions that make this the right choice over alternatives]."

Include the most important conditions, not an exhaustive list. Three to five is usually right.

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When not to use this pattern

As important as the above. Describe the conditions where a different pattern or approach is more appropriate.

For each exclusion, name the alternative: "If [condition], use [pattern or component name] instead."

This section prevents misapplication more than any amount of positive guidance.

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Composition

Describe how the pattern is assembled from its component parts. This is not a code implementation guide — it is a structural description that works for designers and developers alike.

Cover:

• Which components are required vs optional
• The structural relationship between components (which wraps which, what order, what dependencies)
• Any layout or spacing rules that are part of the pattern
• Responsive behaviour: does the pattern change structure at different breakpoints?

If the pattern has multiple variants (e.g. an inline form validation and a summary form validation are both valid sub-patterns), document each variant's composition separately.

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How it works

The interaction, step by step, from the user's side: what they see first, what they do, what the system does in response, where it ends. Five to eight numbered steps. This is the section a new designer reads to understand the pattern before the composition or the states make sense; the public pattern libraries that people trust (GOV.UK, USWDS) all have one.

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State coverage

Document every state the pattern can be in. Patterns fail most often at state boundaries — the transitions between states, not the states themselves — and a reader (or an agent) building from the page needs each transition spelled out.

For each state the pattern can occupy:

• Name the state clearly (e.g. Empty, Loading, Populated, Error, Submitting, Success)
• Describe what the user sees and can do in this state
• Describe the transition to the next state (what triggers it, what changes)
• Identify which components are visible, hidden, or change variant in this state

Common states to check for: default/resting, loading/pending, empty/no data, populated/active, error/invalid, success/complete, disabled/locked, partially complete.

Put the transitions in a table so nothing is implied:

If a state is not applicable, say so explicitly — "This pattern does not have an error state because [reason]." Silence is ambiguity. Ambiguity is drift.

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