Review of popular AI coding tools tweaks

This is a short, practical analysis of how instruction-file formats differ, why some are more popular than others, and what you should use in real projects.

Introduction

Modern AI coding tools (Claude, Copilot, Cursor, etc.) let you add project-level instructions so the agent writes code that fits your style and rules.
Different vendors introduced different files: CLAUDE.md, AGENTS.md, .cursor/rules, .github/instructions.

Even though they look similar, adoption and usage vary a lot, please see the numbers:

Instrument Usages
CLAUDE.md 342k
AGENTS.md 194k
.cursor/rules 101k
.github/instructions 31.7k

Below is a clean breakdown of why and what you should do for each mentioned instrument.

CLAUDE.md vs AGENTS.md

What They Are

  • CLAUDE.md — Anthropic-specific instruction file. Claude auto-loads it into context.
  • AGENTS.md — Vendor-neutral file originally proposed for Codex-style agents; now increasingly supported by multiple tools.

Why CLAUDE.md Is More Popular

  1. Claude loads it automatically → zero setup friction.
  2. Claude Code promoted it heavily → became part of Claude’s workflow.
  3. AGENTS.md isn’t tied to any one product, so many developers simply didn’t know about it.

Practical Differences

Feature CLAUDE.md AGENTS.md
Vendor support Claude only Multi-vendor (Claude, Copilot, others)
Auto inclusion Yes Depends on agent
Typical use Claude coding sessions Generic project-wide AI guidance

When to Use What

  • Use CLAUDE.md if you primarily code inside Claude desktop/web.
  • Use AGENTS.md if you want one shared instruction file for multiple AI tools.
  • Many teams: Create AGENTS.md → copy/symlink it as CLAUDE.md.

'.cursor/rules' vs '.github/instructions'

What They Are

  • .cursor/rules — Cursor IDE’s project rules. Simple to add, widely shared.
  • .github/instructions — GitHub Copilot’s rules folder for file-type-specific instructions.

Why '.cursor/rules' Are More Popular

  1. Cursor launched the concept early → more repos included it publicly.
  2. Easy to use - drop simple .mdc files, no complex syntax.
  3. Huge community making rule packs for frameworks (React, Django, Rust, etc.).
  4. Copilot’s instructions arrived later, and many users don’t commit them to repos.

Practical Differences

Feature .cursor/rules .github/instructions
Maturity Older and widely adopted Newer, still growing
Complexity Very simple More structured (applyTo patterns)
Sharing Many community templates Few templates publicly available

When to Use What

  • If you use Cursor IDE, stick with .cursor/rules.
  • If you use Copilot, use .github/instructions/*.instructions.md, especially for scoped rules (SQL, tests, frontend, etc.).
  • If you use both tools - keep a single master rules file and generate both .cursor/rules and .github/instructions from it.

Does Any Approach Improve Model Performance?

Yes — but not because of file type, rather because of how well the rules are written.

  • Claude handles large rule sets well because of its big context window.
  • Copilot benefits from scoped rules so it doesn’t get overwhelmed by irrelevant info.
  • Cursor follows Claude’s strengths → global rules work fine.

The real performance boost comes from:

  • keeping rules short and clear
  • splitting instructions by domain (e.g., SQL rules separate from UI rules)
  • using actionable bullet points instead of essays

Sample Differences Observed (10–15 File Comparison Summary)

Common patterns across real repositories:

  • All files include: coding style, folder structure, testing instructions.
  • Claude.md files usually contain:
    • setup commands
    • “never do X” sections
    • short philosophy (“prefer smaller PRs”, “do not rewrite files”)
  • AGENTS.md files are more “neutral”:
    • project description
    • architecture notes
    • short rules for tools and commands

Cursor rule files typically include:

  • tech-stack-specific rules (react.mdc, fastapi.mdc)
  • “don’t touch generated files”
  • UI framework opinions (“use Tailwind”, “put hooks in /hooks”)

GitHub instructions files are often smaller because they are scoped:

  • sql.instructions.md only contains database safety rules
  • tests.instructions.md describes how to write unit tests
  • frontend.instructions.md explains style/layout conventions

Conclusion

  • CLAUDE.md wins in popularity because it’s tightly integrated with Claude.
  • AGENTS.md is better as a tool-agnostic standard, especially now that Copilot reads it.
  • .cursor/rules are more widespread than .github/instructions because Cursor users committed them earlier and shared templates widely.
  • Performance doesn't depend on the file type, only on how well instructions are written and scoped.

Best practice: Keep one clean rules file and reuse it across Claude, Cursor, Copilot, and others.

Useful links: