I built a CLI that writes AI rules once for Claude Code, Cursor, and Codex

Every AI coding tool has its own rule format. Claude Code uses .claude/rules/*.md. Cursor uses...

Every AI coding tool has its own rule format.

Claude Code uses .claude/rules/*.md. Cursor uses .cursor/rules/*.mdc. Codex uses .codex/AGENTS.md.

If you use more than one tool, you end up copy-pasting rules between formats, and they inevitably drift apart. On top of that, every prompt loads ALL your rules — even when most of them are irrelevant — wasting tokens and degrading response quality.

I built ai-nexus to fix both problems.

What is ai-nexus?

ai-nexus is a CLI tool that lets you write AI coding rules once in plain Markdown and deploy them across Claude Code, Cursor, and Codex automatically.

• Claude Code → .claude/rules/ with semantic routing (only relevant rules loaded per prompt)
• Cursor → .cursor/rules/*.mdc with auto-converted frontmatter
• Codex → .codex/AGENTS.md aggregated from all your rules

One source of truth. Every tool stays in sync.

Quick start

The interactive wizard asks which tools you use, which rule categories you want, and sets everything up — hooks, settings, symlinks, format conversion. Done in 30 seconds.

npx ai-nexus install

Or quick install with defaults:

npx ai-nexus install -q

Or use your team's rules:

npx ai-nexus install --rules github.com/your-org/team-rules

Key features

Semantic Router — load only what you need

Most setups load every rule file on every prompt. If you have 30+ rules, that's a lot of wasted context.

ai-nexus includes a Semantic Router that runs as a Claude Code hook on each prompt. It analyzes your prompt and picks only the 2-3 rules you actually need.

• With AI routing (recommended): GPT-4o-mini or Claude Haiku selects rules. Cost: ~$0.50/month.
• Without AI (free fallback): Keyword matching activates rules based on words in your prompt.

Result: better AI responses + lower token costs.

Example output:

$ npx ai-nexus test "write a react component with hooks"

Selected rules (3):

• rules/essential.md
• rules/react.md
• skills/react.md

Write once, deploy everywhere

Write a single .md rule file with a description in the frontmatter. ai-nexus automatically converts it to:

• .mdc format for Cursor (with description and alwaysApply frontmatter)
• Aggregated AGENTS.md for Codex
• Semantic-routed .md for Claude Code

No more copy-pasting between formats.

Team rules via Git

Share rules across your entire team with a Git repository:

npx ai-nexus install --rules github.com/acme/team-rules

When rules are updated:

npx ai-nexus update

Updates are non-destructive — your local customizations are never overwritten. Only new files from the source are added.

Community marketplace

Browse, search, install, and remove community-contributed rules — from your browser or CLI:

npx ai-nexus browse

Search and download from the CLI:

npx ai-nexus search react

npx ai-nexus get react.md

Anyone can contribute rules via PR. They become available immediately after merge — no npm publish needed.

How each tool integration works

Claude Code — Semantic Router A hook runs on every prompt. It moves relevant rules into .claude/rules/ (active) and parks the rest in rules-inactive/. Only active rules are loaded into context.

Cursor — Rule Converter ai-nexus converts your .md rules to Cursor's .mdc format, automatically adding frontmatter. After that, Cursor's own built-in semantic search handles the filtering.

Codex — Aggregated Rules All individual rule files are merged into a single AGENTS.md file, loaded at session start.

All commands

• install — Interactive setup wizard
• install -q — Quick install with defaults
• init — Install in current project
• update — Sync latest rules (respects local changes)
• list — Show installed rules
• test — Preview which rules would load
• search — Search community registry
• get — Download a community rule
• add — Add rules from a Git repo
• remove — Remove a rule source
• browse — Open marketplace in browser
• doctor — Diagnose installation issues
• uninstall — Remove ai-nexus

Links

• GitHub
• npm
• Homepage
• Documentation

If you use multiple AI coding tools and are tired of managing rules separately, give it a try:

npx ai-nexus install

Feedback, issues, and rule contributions are all welcome!

What about you? How do you manage your AI coding rules across different tools? Do you copy-paste between formats, or have you found a better workflow? I'd love to hear what's working (or not working) for you.