Modular Code Enforcement Agent Skill

Modular Code Architecture — Zero Tolerance Policy

This rule is NON-NEGOTIABLE. Violations BLOCK all further work until resolved.

Rule 1: index files are ENTRY POINTS, NOT dumping grounds

index files (index.ts, __init__.py, index.js, etc.) MUST ONLY contain:

• Re-exports (export { ... } from "./module")
• Factory function calls that compose modules
• Top-level wiring/registration (hook registration, plugin setup)

index files MUST NEVER contain:

• Business logic implementation
• Helper/utility functions
• Type definitions beyond simple re-exports
• Multiple unrelated responsibilities mixed together

If you find mixed logic in an index file: Extract each responsibility into its own dedicated file BEFORE making any other changes. This is not optional.

Rule 2: No Catch-All Files — utils/helpers/service are CODE SMELLS

A single utils, helpers, service, or common file is a gravity well — every unrelated function gets tossed in, and it grows into an untestable, unreviewable blob.

These file names are BANNED as top-level catch-alls. Instead:

| Anti-Pattern | Refactor To |

|--------------|-------------|

| utils with formatDate(), slugify(), retry() | date-formatter, slugify, retry |

| service handling auth + billing + notifications | auth-service, billing-service, notification-service |

| helpers with 15 unrelated exports | One file per logical domain |

Design for reusability from the start. Each module should be:

• Independently importable — no consumer should need to pull in unrelated code
• Self-contained — its dependencies are explicit, not buried in a shared grab-bag
• Nameable by purpose — the filename alone tells you what it does

If you catch yourself typing utils or service, STOP and name the file after what it actually does.

Rule 3: Single Responsibility Principle — ABSOLUTE

Every source file MUST have exactly ONE clear, nameable responsibility.

Self-test: If you cannot describe the file's purpose in ONE short phrase (e.g., "parses YAML frontmatter", "matches rules against file paths"), the file does too much. Split it.

| Signal | Action |

|--------|--------|

| File has 2+ unrelated exported functions | SPLIT NOW — each into its own module |

| File mixes I/O with pure logic | SPLIT NOW — separate side effects from computation |

| File has both types and implementation | SPLIT NOW — types file + implementation file |

| You need to scroll to understand the file | SPLIT NOW — it's too large |

Rule 4: 200 LOC Hard Limit — CODE SMELL DETECTOR

Any source file exceeding 200 lines of code (excluding prompt strings, template literals containing prompts, and markdown content) is an immediate code smell.

When you detect a file > 200 LOC:

• STOP current work
• Identify the multiple responsibilities hiding in the file
• Extract each responsibility into a focused module
• Verify each resulting file is < 200 LOC and has a single purpose
• Resume original work

Prompt-heavy files (agent definitions, skill definitions) where the bulk of content is template literal prompt text are EXEMPT from the LOC count — but their non-prompt logic must still be < 200 LOC.

How to Count LOC

Count these (= actual logic):

• Import statements
• Variable/constant declarations
• Function/class/interface/type definitions
• Control flow (if, for, while, switch, try/catch)
• Expressions, assignments, return statements
• Closing braces } that belong to logic blocks

Exclude these (= not logic):

• Blank lines
• Comment-only lines (//, /* */, /** */)
• Lines inside template literals that are prompt/instruction text
• Lines inside multi-line strings used as documentation/prompt content

Quick method: Read the file → subtract blank lines, comment-only lines, and prompt string content → remaining count = LOC.

Example:

// 1  import { foo } from "./foo";          ← COUNT
// 2                                         ← SKIP (blank)
// 3  // Helper for bar                      ← SKIP (comment)
// 4  export function bar(x: number) {       ← COUNT
// 5    const prompt = `                     ← COUNT (declaration)
// 6      You are an assistant.              ← SKIP (prompt text)
// 7      Follow these rules:                ← SKIP (prompt text)
// 8    `;                                   ← COUNT (closing)
// 9    return process(prompt, x);           ← COUNT
// 10 }                                      ← COUNT

→ LOC = 5 (lines 1, 4, 5, 9, 10). Not 10.

When in doubt, round up — err on the side of splitting.

How to Apply

When reading, writing, or editing ANY source file:

• Check the file you're touching — does it violate any rule above?
• If YES — refactor FIRST, then proceed with your task
• If creating a new file — ensure it has exactly one responsibility and stays under 200 LOC
• If adding code to an existing file — verify the addition doesn't push the file past 200 LOC or add a second responsibility. If it does, extract into a new module.

Inspired by: oh-my-opencode modular-code-enforcement rule