Claude Code How-To Guide
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Skills

name: claude-md description: Create or update CLAUDE.md files following best practices for optimal AI agent onboarding

User Input

$ARGUMENTS

You MUST consider the user input before proceeding (if not empty). User may specify: - create - Create new CLAUDE.md from scratch - update - Improve existing CLAUDE.md - audit - Analyze and report on current CLAUDE.md quality - A specific path to create/update (e.g., src/api/CLAUDE.md for directory-specific instructions)

Core Principles

LLMs are stateless: CLAUDE.md is the only file automatically included in every conversation. It serves as the primary onboarding document for AI agents into your codebase.

The Golden Rules

  1. Less is More: Frontier LLMs can follow ~150-200 instructions. Claude Code's system prompt already uses ~50. Keep your CLAUDE.md focused and concise.

  2. Universal Applicability: Only include information relevant to EVERY session. Task-specific instructions belong in separate files.

  3. Don't Use Claude as a Linter: Style guidelines bloat context and degrade instruction-following. Use deterministic tools (prettier, eslint, etc.) instead.

  4. Never Auto-Generate: CLAUDE.md is the highest leverage point of the AI harness. Craft it manually with careful consideration.

Execution Flow

1. Project Analysis

First, analyze the current project state:

  1. Check for existing CLAUDE.md files:
  2. Root level: ./CLAUDE.md or .claude/CLAUDE.md
  3. Directory-specific: **/CLAUDE.md

  4. Global user config: ~/.claude/CLAUDE.md

  5. Identify the project structure:

  6. Technology stack (languages, frameworks)
  7. Project type (monorepo, single app, library)

  8. Development tools (package manager, build system, test runner)

  9. Review existing documentation:

  10. README.md
  11. CONTRIBUTING.md
  12. package.json, pyproject.toml, Cargo.toml, etc.

2. Content Strategy (WHAT, WHY, HOW)

Structure CLAUDE.md around three dimensions:

WHAT - Technology & Structure

  • Technology stack overview
  • Project organization (especially important for monorepos)
  • Key directories and their purposes

WHY - Purpose & Context

  • What the project does
  • Why certain architectural decisions were made
  • What each major component is responsible for

HOW - Workflow & Conventions

  • Development workflow (bun vs node, pip vs uv, etc.)
  • Testing procedures and commands
  • Verification and build methods
  • Critical "gotchas" or non-obvious requirements

3. Progressive Disclosure Strategy

For larger projects, recommend creating an agent_docs/ folder:

agent_docs/
  |- building_the_project.md
  |- running_tests.md
  |- code_conventions.md
  |- architecture_decisions.md

In CLAUDE.md, reference these files with instructions like:

For detailed build instructions, refer to `agent_docs/building_the_project.md`

Important: Use file:line references instead of code snippets to avoid outdated context.

4. Quality Constraints

When creating or updating CLAUDE.md:

  1. Target Length: Keep it under a few hundred lines; shorter is better
  2. No Style Rules: Remove any linting/formatting instructions
  3. No Task-Specific Instructions: Move to separate files
  4. No Code Snippets: Use file references instead
  5. No Redundant Information: Don't repeat what's in package.json or README

5. Essential Sections

A well-structured CLAUDE.md should include:

# Project Name

Brief one-line description.

## Tech Stack
- Primary language and version
- Key frameworks/libraries
- Database/storage (if any)

## Project Structure
[Only for monorepos or complex structures]
- `apps/` - Application entry points
- `packages/` - Shared libraries

## Development Commands
- Install: `command`
- Test: `command`
- Build: `command`

## Critical Conventions
[Only non-obvious, high-impact conventions]
- Convention 1 with brief explanation
- Convention 2 with brief explanation

## Known Issues / Gotchas
[Things that consistently trip up developers]
- Issue 1
- Issue 2

6. Anti-Patterns to Avoid

DO NOT include: - Code style guidelines (use linters) - Documentation on how to use Claude - Long explanations of obvious patterns - Copy-pasted code examples - Generic best practices ("write clean code") - Instructions for specific tasks - Auto-generated content - Extensive TODO lists

7. Validation Checklist

Before finalizing, verify:

  • [ ] Kept under a few hundred lines; shorter is better
  • [ ] Every line applies to ALL sessions
  • [ ] No style/formatting rules
  • [ ] No code snippets (use file references)
  • [ ] Commands are verified to work
  • [ ] Progressive disclosure used for complex projects
  • [ ] Critical gotchas are documented
  • [ ] No redundancy with README.md

Output Format

For create or default:

  1. Analyze the project
  2. Draft a CLAUDE.md following the structure above
  3. Present the draft for review
  4. Write to the appropriate location after approval

For update:

  1. Read existing CLAUDE.md
  2. Audit against best practices
  3. Identify:
  4. Content to remove (style rules, code snippets, task-specific)
  5. Content to condense
  6. Missing essential information
  7. Present changes for review
  8. Apply changes after approval

For audit:

  1. Read existing CLAUDE.md
  2. Generate a report with:
  3. Current line count vs target
  4. Percentage of universally-applicable content
  5. List of anti-patterns found
  6. Recommendations for improvement
  7. Do NOT modify the file, only report

AGENTS.md Handling

If the user requests AGENTS.md creation/update:

Since v2.1.277, Claude Code reads AGENTS.md directly as project instructions β€” but only when the working directory and every directory above it contain no CLAUDE.md, .claude/CLAUDE.md, or CLAUDE.local.md. ~/.claude/CLAUDE.md, managed CLAUDE.md, and .claude/rules/ do not count for that check and keep loading alongside. Which files are read is controlled by Project instructions in /config: claude-md-or-agents-md (default), claude-md-and-agents-md, claude-md, or managed-only. Where direct reading is unavailable β€” versions before v2.1.277 (before v2.1.281 on Bedrock/Vertex/Foundry, LLM gateways, or with telemetry disabled), or the first session after upgrading β€” fall back to importing it from CLAUDE.md with @AGENTS.md, or symlinking CLAUDE.md to it.

AGENTS.md is a cross-tool project-context file β€” the same category of document as CLAUDE.md, not an agent-definition format. It exists so several coding agents can share one set of project conventions: - Build, test, and lint commands - Code style and architectural conventions - Repository layout and where things live

Subagents are defined separately, in .claude/agents/*.md β€” not in AGENTS.md.

Apply similar principles: - Keep focused and concise - Use progressive disclosure - Reference external docs instead of embedding content

Notes

  • Always verify commands work before including them
  • When in doubt, leave it out - less is more
  • The system reminder tells Claude that CLAUDE.md "may or may not be relevant" - the more noise, the more it gets ignored
  • Monorepos benefit most from clear WHAT/WHY/HOW structure
  • Directory-specific CLAUDE.md files should be even more focused

Last Updated: September 26, 2026 Claude Code Version: 2.1.283 Sources: - https://code.claude.com/docs/en/skills - https://code.claude.com/docs/en/memory#agents-md - https://code.claude.com/docs/en/memory#when-agents-md-support-is-unavailable Compatible Models: Claude Fable 5, Claude Opus 5, Claude Sonnet 5, Claude Sonnet 4.6, Claude Opus 4.8, Claude Haiku 4.5

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