Keystone keeps reusable rules and Skills in profiles, writes the right files into each project, and turns outside edits into a review queue before they become shared truth.
Native macOS 14+ · Local-first · Free to download
One library
Reusable rules and Skills live in a profile — not scattered across one-off markdown files.
Linked, not copied
Projects stay connected. Each one gets the agent files it needs, in the format each tool expects.
Profiles, not piles
Switch between iOS, web, client, or personal setups without rewriting everything.
Materializes each agent's format
Claude Code, Cursor, Copilot, Windsurf, Gemini CLI, Codex — plus any tool that reads the open AGENTS.md standard.
Keystone does not just copy the same text everywhere. It keeps AGENTS.md as the canonical project file, then writes mirrors, imports, generated copies, or rule directories where each tool expects them.
AGENTS.md stays the readable source each project can keep even if you stop using Keystone.
Cursor, Copilot, Windsurf, Claude, Gemini, and Codex each get the path they actually read.
Claude
CLAUDE.md
Symlink or @AGENTS.md import file.
Gemini
GEMINI.md
Symlink or @AGENTS.md import file.
Cursor
.cursor/rules/*.mdc
Generated rule files with Cursor-friendly frontmatter.
Copilot
.github/copilot-instructions.md
A generated copy in the path GitHub expects.
Windsurf
.windsurf/rules/*.md
Directory-style rules instead of one giant file.
Codex
AGENTS.md
Reads the canonical project instructions directly.
Agent instructions are easy to create. They are harder to keep current across projects, machines, and tools after real work starts changing them.
Most sync tools export files once. Keystone stays connected to your projects: it writes the right files, watches for outside edits, and keeps your profile as the source that evolves.
Edit a project file outside Keystone, review the detected change, then pull it into the profile and propagate it everywhere else.
Link a folder and choose which agents it should support. Keystone writes AGENTS.md, symlinks, generated rule files, and Skill folders.
Keep separate libraries for iOS, web, work, personal, or clients. Each linked project belongs to exactly one profile.
Profiles sync across your Macs with no Keystone account. Linked project folders stay local to each device.
Manage Skills once in your home directory and mirror them to Skills-capable agents, available across every project.
Sandboxed and careful with existing files. Keystone adopts what it can, preserves unmanaged content, and never silently clobbers your work.
Link a project and Keystone offers to import its existing AGENTS.md or CLAUDE.md into your library. Migration is one click, not an afternoon.
Accepted a project change into your profile and regret it? One click restores the previous state — the review flow is never a one-way door.
Everything Keystone writes is plain markdown in your repo. Export a profile as a standalone AGENTS.md, copy it, or share it — delete the app and your files still work.
Local-first by default: Keystone works with folders you explicitly link, stores profiles on your Mac, uses your private iCloud when sync is enabled, and does not require a Keystone account.
When a rule or Skill changes outside Keystone, the project shows an incoming-change badge. Open the review sheet, compare the project version with the profile version, choose what to keep, then accept and sync.
Keystone classifies new sections, edited rules, changed Skills, and removals so you can pull only the useful edits into the profile.
If both the profile and project changed since the last sync, Keystone shows both versions instead of guessing. Pick the project version when it should become the new shared truth.
Keystone watches linked files for edits made by you, an agent, or another editor.
A three-way diff separates added, edited, removed, and conflicting changes.
Accepted changes update the profile, then Keystone syncs them back to every linked project.
Keystone is not asking you to hand-edit six tool-specific files. You work in profiles, add reusable rules and Skills, then let Keystone materialize the right files per project.
Use iOS, web, personal, or client profiles so each project gets the right rule set.
Start from templates, import existing markdown, or paste a Skill link.
Choose which agents the project uses; Keystone writes only those targets.
Push profile updates out, and pull useful project edits back into the shared library.
Rules are named markdown sections. Toggle which linked projects receive each one, then push the profile when you are ready.
Turn agent targets on or off project by project: canonical AGENTS.md, symlinks, generated rule files, and Skill folders.
These are the parts that make Keystone more than a markdown editor: separate libraries for different work, cloud-synced profiles, and reusable Skills that can be global or project-scoped.
Profiles keep rules, Skills, and linked projects separate. Use a tight iOS profile for native apps, a web profile for TypeScript, and a personal profile for everything else.
Global Skills live once in your home directory and are mirrored to each supported agent, so commands like review-diff and write-tests follow every project.
Free to download from the Mac App Store. Unlock Pro when Keystone becomes the rule library for all your projects — a one-time lifetime purchase is available.
Everything you need to try Keystone on a project or two.
For managing your rules across everything you build.
No. When you link a folder, Keystone offers to import the rules it finds into your library first. It never replaces a real file it didn't create — if a conflicting file exists, Keystone leaves it alone and tells you.
Plain files, exactly where each tool expects them: a readable AGENTS.md, symlinks or import stubs for Claude and Gemini, generated rule files for Cursor, Copilot, and Windsurf, and Skill folders. No hidden metadata, no proprietary format. Commit them like any other file.
Nothing breaks. Every project keeps its working AGENTS.md and tool files. You can also export any profile as a standalone markdown file at any time.
That's the point of Keystone. It detects outside edits, classifies them with a three-way diff — added, edited, removed, or conflicting — and queues them for review. You choose what gets promoted into the shared library, and you can undo an accepted change afterward.
No. Keystone has no account system and no telemetry-driven backend. Profiles are stored on your Mac; optional sync across your Macs uses your private iCloud.
Free includes one profile, two linked projects, every agent format, and Skills. Pro removes the limits and adds iCloud sync across Macs — with a one-time lifetime unlock if you dislike subscriptions.
Built for macOS 14 and later. Free to download — link your first project in under a minute.
Download on the Mac App Store