Keystone
Native macOS app

One source of truth for
every AI coding agent.

Write your rules and skills once in a canonical AGENTS.md. Keystone materializes the right file for Claude, Cursor, Copilot, Windsurf, Gemini and Codex — in every project, kept in sync across every Mac.

Download on the Mac App Store See how it works

macOS 14 Sonoma or later · Free with an optional Pro upgrade

my-app — one edit, every agent

You edit once

AGENTS.md source of truth 
# Architecture
- Use MVVM, inject dependencies
- Prefer async/await over Combine

# Skills
- release-notes
- localize-check

Keystone materializes

  • CLAUDE.md→ AGENTS.md
  • GEMINI.md→ AGENTS.md
  • .cursor/rules/*.mdcgenerated
  • .github/copilot-instructions.mdgenerated
  • .windsurf/rules/*.mdgenerated
  • .agents/skills/2 skills mirrored

Speaks every agent's format

AGENTS.md CLAUDE.md .cursor/rules copilot-instructions.md .windsurf/rules GEMINI.md Codex

Stop copy-pasting rules between six different files.

Keystone treats AGENTS.md as the keystone that holds every agent together — everything else is a mirror it keeps honest.

One canonical file

Your rules live in a single AGENTS.md. Edit it once — Keystone never scatters conflicting copies across your repo.

Every agent, its own format

Claude and Gemini get a symlink or @AGENTS.md import. Cursor, Copilot and Windsurf get correctly-formatted generated files with frontmatter.

Agent Skills, managed

Author reusable Skills once and mirror them into each agent's skills folder — globally in your home directory or scoped to a single project.

Switchable profiles

Keep a work profile, a personal profile, a client profile — each a full library of rules and skills. Switch the whole set with one click.

Synced across your Macs

Your profiles follow you over iCloud. Change a rule on your laptop and it's already there on your desktop — both directions, no accounts, no server.

Safe by design

Sandboxed, on-device, and non-destructive. Edit a generated CLAUDE.md by hand and Keystone promotes the change back to your source — it never silently clobbers your work.

From one file to every agent, automatically.

Three steps between a wall of duplicated config and a single library that keeps itself honest.

1

Link a project

Point Keystone at any folder. It reads whatever agent files already exist and adopts them — nothing is overwritten.

2

Edit rules & skills once

Manage your canonical rules and Skills in a clean native editor with live Markdown preview.

3

Materialize everywhere

Keystone writes the right file for each agent you've enabled and keeps them in sync as you work.

Keystone's arch: pale voussoir stones held together by a single blue keystone at the apex, standing in an open landscape.

A living library, not a one-time export.

Most tools generate agent files once and forget them. Keystone keeps the relationship alive: edit the source or any mirror, on any Mac, and the change propagates everywhere it belongs.

  • Bidirectional. A hand-edit in a generated file is promoted back to your profile, then pushed to the others.
  • Project-centric. Each project keeps its own targets and its own included rules and skills.
  • Yours to keep. Everything is a plain file on disk. Stop using Keystone and your rules stay exactly where they are.

Profiles

Work
active
Personal
12 rules · 4 skills
Open source
8 rules · 2 skills
Synced across your Macs over iCloud

Simple, honest pricing

Every agent format is free, forever. Pro lifts the limits when you're managing your whole setup.

Free

Everything you need to try Keystone on a project or two.

  • Up to 1 profile and 2 linked projects
  • All agent formats and Skills
  • Symlink or import link styles
Pro

Keystone Pro

For managing your rules across everything you build.

  • Unlimited profiles and projects
  • iCloud sync across all your Macs
  • Monthly subscription or one-time lifetime
Upgrade in the app
Keystone

Give your agents one source of truth.

Download Keystone from the Mac App Store. Built for macOS 14 and later.

Download on the Mac App Store