the agent edits, you decide.
Above: a real session, captured live. An agent connected over MCP applies three edits to the open buffer (a grammar fix, a typo, a missing section); each lands selected and unsaved. Then plain undo, the same step Cmd+Z triggers, peels the agent's edits off one at a time until the original text is back and the buffer is clean. One agent edit, one undo step; disk is never touched until you save.
A quoin (pronounced "coin") is the letterpress wedge that locks loose type into the frame so it can print. That is this editor's job in the agent era: hold the text steady while agents work on it; nothing is committed until you lock it in.
Quoin is a macOS text editor where AI agents are first-class users. An agent connected over MCP reads and edits the live buffer, unsaved changes included. Every agent edit lands as one undoable step on the normal undo stack, and nothing touches disk until you press Cmd+S: the agent proposes, you dispose.
Beyond the agent surface, it is a Sublime-class editor: native tabs, tree-sitter highlighting, Goto Anything, command palette, split panes, multi-cursor, hot exit. Swift + AppKit, pure SwiftPM, macOS 14+, no Xcode.app required.
Quoin ships no model, no API keys, no chat pane. It is the instrument: you bring whatever agent you want, over MCP, and swap it the day a better one exists. Editors that embed a single vendor's agent make the editor the gatekeeper; here the editor's whole job is to give any agent honest access to the buffer and give you the only save button. It is one of a pair of agent-native instruments built on the same principle (bounded verbs for the agent, commit rights for the human); the other is a CBCT viewer for medical imaging, at rezamotaghi.com.
swift test # 79 unit tests
Scripts/bundle-app.sh # -> build/Quoin.app
open build/Quoin.appFull guide: QUICKSTART.md, also in-app via Help > Quickstart Guide. Architecture and invariants: ARCHITECTURE.md.
The running app listens on a local unix socket (no network listener, local-only by construction). The bundled shim exposes that socket as an MCP server:
claude mcp add quoin -- "$(pwd)/build/Quoin.app/Contents/MacOS/QuoinMCP"Read tools: quoin_list_open_documents, quoin_read_buffer (live
buffer, including unsaved edits), quoin_get_selection,
quoin_open_file (path + line), quoin_list_commands,
quoin_run_command. Write tools: quoin_replace_selection,
quoin_apply_edit (offset range), quoin_set_text.
Each write is registered as its own inverse on the document's undo manager, so
Cmd+Z peels agent edits off one at a time, back to a pristine buffer. Edits
mark the document dirty like typing does; the file on disk changes only when
you save. Turn the whole surface off with "agent_server": false in settings.
ln -s "$(pwd)/Scripts/quoin" /usr/local/bin/quoin # once, from the repo root
quoin notes.md # open a file
quoin src/main.swift:42 # open at line 42quoin drives the quoin://open?file=...&line=... URL scheme; anything
else on the machine can use those links directly.
| Key | Action |
|---|---|
| Cmd+P | Goto Anything (fuzzy file open in the project folder) |
| Cmd+Shift+P | Command Palette |
| Cmd+D | Select word, then add next occurrence (multi-cursor) |
| Ctrl+Cmd+G | Select all occurrences |
| Escape | Collapse to one caret |
| Cmd+Alt+2 | Toggle split editor (two views, one buffer) |
| Cmd+F | Find; Cmd+Alt+F find and replace |
| Cmd+Shift+M | Markdown preview |
| Cmd+Shift+[ / ] | Previous / next tab |
Tree-sitter highlighting ships for Swift, Python, JSON, and Markdown; JSONC uses a hand-rolled lexer, and other file types open unhighlighted as plain text. Hot exit is on by default: quit and relaunch restores every tab, including unsaved buffers (graceful quit; a force-kill loses them). If anything rewrites a file you have unsaved edits in, a banner offers Reload From Disk / Keep My Edits.
Sublime key names, JSONC, hot-reloaded on save:
- Defaults (documented):
Settings/default-settings.jsonc(ships in the app) - Your overrides:
~/Library/Application Support/Quoin/settings.jsonc - Color schemes:
Settings/schemes/*.jsonc(marianadark,breakerslight,"theme": "auto"follows macOS)
Small, tested, one-concern PRs are welcome: CONTRIBUTING.md has the build steps and conventions. Security reports go through private advisories, not issues: SECURITY.md. Release history: CHANGELOG.md.
MIT, see LICENSE.
Built by Dr. Reza Motaghi. More at rezamotaghi.com.