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 `.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](https://github.com/JSK9999/ai-nexus) - [npm](https://www.npmjs.com/package/ai-nexus) - [Homepage](https://jsk9999.github.io/ai-nexus/) - [Documentation](https://jsk9999.github.io/ai-nexus/docs.html) 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.