Quick rule -- write a rule from known patterns

You are writing a Shopify Liquid rule for a well-documented topic. This skill is the fast path: lean on Shopify's official documentation and your own knowledge rather than mining local themes.

The topic is: $ARGUMENTS

Read the reference files in this skill's directory before starting:

• references/rule-template.md -- the format every rule must follow
• references/existing-coverage.md -- what Shopify's cursor rules already cover (avoid duplicating)

When to use this skill vs /research-shopify-rule

If you discover during Phase 1 that the topic is more complex than expected, stop and suggest switching to /research-shopify-rule before investing time in a draft.

Phase 1 -- Scope

1.1 Parse the topic

Break down $ARGUMENTS:

• What Liquid objects, filters, tags, or Shopify features are involved?
• Is this a single technique or does it combine multiple concepts?
• What complexity level does this feel like: basic, intermediate, or advanced?

1.2 Check for overlap

Use the three-level overlap check:

1. Read references/existing-coverage.md -- does this overlap with Horizon's cursor rules? If so, note what the existing rules cover and focus on what they do NOT cover.
2. Check rules/INDEX.md for existing rules on the topic. If a related rule exists, determine whether to extend it or create a new one.
3. If shopify-themes/horizon/ is present, scan its .cursor/rules/ for the latest coverage. This takes priority over the static summary.

Also check rules/BACKLOG.md -- if this topic is there, note its scope and evidence.

1.3 Complexity guardrail

Evaluate whether this topic is suitable for the quick path. Flag it as too complex if any of these are true:

• The official Shopify docs do not adequately document the pattern
• The topic involves undocumented Liquid behavior or workarounds
• Multiple interacting patterns are needed (more than one rule's worth of content)
• Real-world implementations vary significantly across themes and there is no clear best practice
• The topic requires understanding Shopify platform quirks not covered in docs

If the topic is too complex, tell the user:

This topic appears more complex than a quick rule can cover well. Specifically: reason. I recommend using /research-shopify-rule $ARGUMENTS instead, which includes cross-theme research and pattern analysis phases.

Wait for the user to decide before proceeding.

1.4 Quick local scan (optional)

If the shopify-themes/ directory contains themes, do a fast scan for relevant snippets or sections -- but only to supplement web research, not as a primary source. Limit this to a few targeted greps.

If shopify-themes/ is empty or does not exist, skip this step entirely. The quick-rule workflow does not depend on local themes.

1.5 Present scope

Tell the user:

• The topic you understood from their input
• The target rule filename and category
• Any overlap with existing rules or cursor rules
• Whether you plan to create a new rule or extend an existing one
• Confirmation that the topic is suitable for the quick path

Wait for user confirmation before proceeding to Phase 2.

Phase 2 -- Draft

2.1 Web research

Research the topic using Shopify's official documentation. Focus on:

• shopify.dev -- Liquid reference, theme architecture docs, API docs
• Shopify Community forums at community.shopify.dev -- for common gotchas and edge cases
• Links the user provides as additional context

For each key aspect of the pattern, look for:

• Official syntax and parameters
• Documented limitations or caveats
• Official code examples
• Changelog entries (when was this feature added or changed?)

2.2 Write the rule

Draft the rule following the template in references/rule-template.md. Apply these principles:

Frontmatter

• Choose the most appropriate category
• Set complexity to basic or intermediate (if you need advanced, reconsider whether this should be a /research-shopify-rule)
• Include tags that an AI agent would search for when encountering the problem
• List all Liquid objects and filters the pattern uses

Problem section

• Be specific about the gap -- what would an AI agent get wrong without this rule?
• Frame it as a limitation, challenge, or non-obvious behavior

Solution section

• Provide a complete, copy-paste ready code example
• Annotate each step so an AI agent understands the why, not just the what
• Use {% liquid %} blocks for multiline logic (Shopify convention)

How it works section

• Walk through each step of the pattern
• Explain why each line exists

Variations section

• Include alternative approaches if they exist in official documentation
• Note trade-offs for each variation
• If local themes were available and showed an interesting variation, include it with a source reference

Source references section

• Link to the relevant Shopify documentation pages (use full URLs)
• If themes in shopify-themes/ were consulted, include theme file references
• If no local themes were available, state: "Pattern documented from Shopify official documentation."

Edge cases and gotchas

• Pull from documentation warnings, community forum issues, and known Liquid quirks
• Focus on things an AI would not know from reading the basic docs

Related section

• Link to related rules if they exist in rules/
• Suggest topics that could become future rules

2.3 Present draft

Show the complete draft to the user. Ask for feedback. Iterate based on their input.

Phase 3 -- Finalize

1. Write the rule to rules/<category>/<rule-name>.md
   • Use kebab-case for filenames
   • Create the category folder if it doesn't exist yet
2. Update rules/INDEX.md:
   • Add the new rule under the appropriate category heading
   • Format: - [Rule Title](category/rule-name.md) -- one-line description
3. If this topic came from rules/BACKLOG.md, update the entry:
   • Set status to done
   • Add the rule link
4. Suggest 1-2 related topics that could become future rules

Important guidelines

• Never invent Liquid filters, tags, or objects. Only use what exists in Shopify's Liquid implementation.
• When showing code examples, use the {% liquid %} tag for multiline logic blocks.
• Always test that code examples are syntactically valid Liquid.
• If a pattern involves metafields, specify the metafield namespace and type clearly.
• Cross-reference Shopify's official Liquid docs when unsure about object properties or filter behavior.
• The rules are standalone content. Do not reference project-specific paths within rule content.
• Source references should use full URLs for Shopify docs and relative theme paths for local themes (e.g., dawn/snippets/price.liquid).
• This is the fast path. If research is taking significantly longer than expected, reconsider whether /research-shopify-rule would be more appropriate.