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 — with automatic snapshots of the whole library, so you can roll back anytime.
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.
One canonical file, every agent covered
Cursor, Copilot, Devin (Windsurf), and Codex read the open AGENTS.md standard directly; Claude Code and Gemini CLI get link files that point to it.
Keystone keeps AGENTS.md as the canonical project file. Modern tools read it directly; the ones that still want their own file get a link back to it. Leftover legacy formats are imported into the canonical file and cleaned up.
AGENTS.md stays the readable source each project can keep even if you stop using Keystone.
Cursor, Copilot, Devin (Windsurf), and Codex read AGENTS.md natively; Claude and Gemini get link files that point to it.
Claude
CLAUDE.md
Symlink or @AGENTS.md import file.
Gemini
GEMINI.md
Symlink or @AGENTS.md import file.
Cursor
AGENTS.md
Reads it natively; legacy .cursor/rules is imported and removed.
Copilot
AGENTS.md
Reads it natively; legacy copilot-instructions.md is imported and removed.
Devin (Windsurf)
AGENTS.md
Reads it natively; legacy .windsurf/rules is imported and removed.
Codex
AGENTS.md
Reads the canonical project instructions directly.
Most repos already carry a CLAUDE.md for Claude and an AGENTS.md for everything else — half-duplicated and quietly drifting apart. Link the project and Keystone reads both, deduplicates what they share, and turns the rest into one rule set every agent understands.
Sections both files share are recognized and imported once — no copy-paste archaeology.
Where the files disagree, Keystone shows the difference and lets you keep either side, merge them, or write the final wording yourself.
After adoption, AGENTS.md is the canonical file and Claude reads the same rules through it — every agent works from one set instead of two.
Agent instructions are easy to create. They are harder to keep current across projects, machines, and tools after real work starts changing them.
A real pass through Keystone: review incoming changes, inspect the diff, check rules and Skills, switch profiles, then open Global Skills for reusable playbooks.
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, link files for Claude and Gemini, and Skill folders — and offers to clean up legacy per-tool rule files.
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 imports its existing AGENTS.md and CLAUDE.md — merging both into one rule set and resolving their conflicts when a repo has the pair. Migration is a review, not an afternoon.
Accepted a change and regret it? One click undoes it. Keystone also snapshots your library automatically — see how any rule or Skill evolved, diff versions, and restore one item or everything, like Time Machine for your rules.
Send a profile, rule, or Skill as a .keystone file — a teammate double-clicks it and Keystone imports it for them. Everything written to your repo stays plain markdown; 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, link files for Claude and Gemini, 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, nothing more: a readable AGENTS.md, symlinks or import stubs for Claude and Gemini, and Skill folders. Cursor, Copilot, Devin (Windsurf), and Codex read AGENTS.md directly, and Keystone offers to import and remove their legacy rule files. 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.
Yes, at whatever scale you need. An accepted review can be undone with one click — that's free for everyone. Each rule and Skill has a History button in its editor showing how it changed over time, with a diff for every version — restore just that item without touching anything else. And Library History in the profile menu rolls the whole library back to any snapshot. Restoring is a Pro feature, but snapshots are always being saved, so your history is already there when you unlock. The current state is saved first, so a restore is itself reversible.
Export any profile, rule, or Skill as a .keystone file — via AirDrop, the share sheet, or a plain file save. Your teammate double-clicks it and Keystone offers to add a shared profile as their own or merge it into what they already have. Plain markdown export works too, if they don't use Keystone.
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, Skills, and automatic library snapshots. Pro removes the limits and adds iCloud sync across Macs plus Library History restore — 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