fusion-rule-author

Rule Author

Canonical workflow, templates, and references for authoring AI coding assistant rules. Supports GitHub Copilot, Cursor, and Claude Code.

Internal skill. Users interact via the fusion-rules gateway, which routes to editor-specific agents that follow the workflow defined here.

Scope

This skill provides:

• Workflow (Steps 1–7 below) — the guided authoring process
• Templates (assets/) — starter files for each editor format
• References (references/) — tech-stack examples

It does not provide agents. Agents live in fusion-rules/agents/ and reference this skill's assets and workflow.

Required inputs

Mandatory

• Repository context (working directory or repo URL)

Gathered during interview

• Tech stack (languages, frameworks, build tools)
• Code conventions (naming, formatting, patterns)
• Testing expectations (framework, coverage, style)
• Documentation preferences (comments, TSDoc/JSDoc, README standards)
• Commit and PR conventions
• Error handling patterns
• Security or compliance constraints
• File/path-specific conventions that need scoped rules

Instructions

Step 1 — Assess current state

Check the repository for existing rule files:

.github/copilot-instructions.md
.github/instructions/*.instructions.md
.cursor/rules/*.md
.cursor/rules/*.mdc
.cursor/rules/**/*.md
.cursor/rules/**/*.mdc
CLAUDE.md
.claude/CLAUDE.md
.claude/rules/*.md
.claude/rules/**/*.md

Report what exists, what is missing, and whether updates or new files are needed.

Step 2 — Scan repository

Before interviewing, scan for existing documentation and configuration that encodes conventions. Extract actionable directives from:

Documentation files:

• README.md — project overview, setup, tech stack
• CONTRIBUTING.md — code style, PR workflow, commit conventions
• AGENTS.md, CLAUDE.md — existing AI instructions
• docs/adr/**, adr/**, docs/decisions/** — Architecture Decision Records
• docs/**/*.md — developer guides, onboarding docs, style guides
• SECURITY.md — security policies
• CODE_OF_CONDUCT.md — collaboration guidelines (rarely rule-relevant)

Configuration files:

• package.json / pyproject.toml / *.csproj — tech stack, scripts, dependencies
• tsconfig.json / jsconfig.json — language settings, strictness
• biome.json / .eslintrc* / .prettierrc* / ruff.toml / .editorconfig — formatting and linting
• .github/workflows/*.yml — CI checks, required validations, test commands
• Dockerfile / docker-compose.yml — runtime environment
• Makefile / Justfile / Taskfile.yml — build and task commands

Code patterns (sample, don't exhaustively read):

• Entry points (src/index.*, src/main.*, app.*) — architecture patterns
• Test files — testing framework, naming conventions, file placement
• Directory structure — architectural boundaries, feature organization

For each source, extract:

1. Concrete conventions that can become imperative directives
2. Build/test/lint commands the AI should know
3. Architecture boundaries or patterns to follow
4. Explicit "do this / don't do that" rules

Skip:

• Implementation details that change frequently
• Content that restates language/framework defaults
• Aspirational rules not enforced by CI or team practice

Present summary of discovered conventions to the developer, organized by area, before proceeding to the interview.

Step 3 — Interview (fill gaps)

Use scan results to skip areas already well-documented. Ask focused questions only for gaps. Cover these areas one at a time:

1. Tech stack — languages, frameworks, runtime, package manager
2. Code style — naming conventions, formatting rules, import ordering
3. Architecture — project structure, key patterns (MVC, hexagonal, etc.)
4. Testing — framework, conventions, coverage expectations
5. Documentation — inline comments style, doc generation, README standards
6. Git workflow — branch naming, commit message format, PR expectations
7. Security — sensitive data handling, auth patterns, compliance rules
8. Path-specific concerns — directories or file types needing specialized guidance

For each area, present what the scan found and ask: "Is this accurate? Anything to add or correct?" Don't re-ask for information already captured.

For each convention needing deeper context, use follow-up questions in assets/creation-follow-up.md — purpose, exceptions, boundaries, voice.

Step 4 — Classify guidance

Separate the gathered conventions into buckets:

GitHub Copilot:

Bucket	Target file	When it activates
Always-on conventions	.github/copilot-instructions.md	Every Copilot interaction
Scoped conventions	.github/instructions/<name>.instructions.md	Only when matching files are open/referenced

Cursor:

Bucket	Target file	When it activates
Always-on conventions	.cursor/rules/<name>.mdc with alwaysApply: true	Every Cursor Agent session
Auto-attached conventions	.cursor/rules/<name>.mdc with globs	When matching files are in context
Agent-selected conventions	.cursor/rules/<name>.mdc with description only	When the Agent decides it is relevant
Manual conventions	.cursor/rules/<name>.mdc (no alwaysApply, no globs)	Only when @-mentioned in chat

Claude Code:

Bucket	Target file	When it activates
Always-on conventions	CLAUDE.md or .claude/CLAUDE.md	Every Claude Code session
Scoped conventions	.claude/rules/<name>.md with paths frontmatter	When Claude reads matching files
Unconditional rule	.claude/rules/<name>.md (no paths)	Every session (like always-on)

Decision rule: If a convention applies to all files in the repo, it belongs in root / always-on instructions. If it applies only to specific paths or file types, create a scoped rule.

When targeting multiple editors, generate parallel files with equivalent content — do not duplicate guidance within a single editor's files.

Step 5 — Draft rule files

Generate files using templates in assets/:

GitHub Copilot:

• Root instructions: use assets/copilot-instructions-template.md
• Scoped instructions: use assets/scoped-rule-template.md with correct applyTo glob

Cursor:

• Use assets/cursor-rule-template.mdc and set frontmatter accordingly

Claude Code:

• Project instructions: use assets/claude-rule-template.md
• Scoped rules: place in .claude/rules/ with paths frontmatter

Quality rules (enforced during drafting):

• Keep instructions concise — actionable directives, not explanations
• Use imperative voice ("Use camelCase for variables", not "Variables should use camelCase")
• Avoid duplicating guidance between root and scoped files
• Validate applyTo / globs / paths glob patterns match intended files
• Warn if total root instructions exceed ~80 lines (risk of context dilution)
• Warn if scoped instruction file exceeds ~50 lines (GitHub Copilot), ~500 lines (Cursor), ~200 lines (Claude Code CLAUDE.md)
• See references/examples.md for concrete good/bad examples
• See assets/quality-checklist.md for full checklist

Step 6 — Review and refine

Present drafted files to the developer. For each file:

1. Show full content
2. Highlight quality warnings (length, broad globs, duplication)
3. Ask for approval or edits

Step 7 — Write files

After approval, write rule files to the repository. Create .github/instructions/, .cursor/rules/, and/or .claude/rules/ directories as needed.

Confirm final file list and paths before writing.

Expected output

• .github/copilot-instructions.md — root instructions file (created or updated)
• .github/instructions/*.instructions.md — zero or more scoped instruction files
• .cursor/rules/*.mdc — zero or more Cursor rule files (when Cursor is targeted)
• CLAUDE.md or .claude/CLAUDE.md — project instructions (when Claude Code is targeted)
• .claude/rules/*.md — zero or more Claude Code scoped rule files
• Summary of what was created/updated and why

Instructions vs skills vs rules — when to use which

Need	GitHub Copilot	Cursor	Claude Code
Always-on coding conventions	copilot-instructions.md	.cursor/rules/*.mdc with alwaysApply: true	CLAUDE.md
File/path-specific guidance	.github/instructions/*.instructions.md	.cursor/rules/*.mdc with globs	.claude/rules/*.md with paths
Task-specific multi-step workflows	A skill (SKILL.md)	.cursor/rules/*.mdc (manual or agent-selected)	Skills / subagents
Agent routing and orchestration	Agent definitions (.agent.md)	.cursor/rules/*.mdc with description	Subagent configs
Simple project-wide instructions	copilot-instructions.md	AGENTS.md	CLAUDE.md

Instructions and rules shape how the AI writes code. Skills define what it can do as structured tasks.

Safety and constraints

Never:

• Embed secrets, tokens, or credentials in rule files
• Generate rules that contradict repository security policies
• Overwrite existing files without showing the diff and getting approval
• Invent conventions — only document what the developer confirms

Always:

• Show drafts before writing any files
• Validate glob patterns against actual repository paths
• Warn on overly broad globs (e.g., **/* captures everything)
• Keep instructions concise and actionable
• Preserve existing content when updating (append or merge, never replace silently)

References

• references/examples.md — concrete examples for different tech stacks
• assets/creation-follow-up.md — per-rule follow-up questions (purpose, exceptions, boundaries, voice)
• assets/frontmatter-scenarios.md — scenario-based frontmatter guide for GitHub Copilot, Cursor, and Claude Code
• assets/copilot-instructions-template.md — starter template for root instructions
• assets/scoped-rule-template.md — starter template for scoped rules
• assets/cursor-rule-template.mdc — starter template for Cursor rules
• assets/claude-rule-template.md — starter template for Claude Code rules
• assets/quality-checklist.md — quality review checklist