Fettlr

A cross-platform desktop app for managing Claude Code's skills, subagents, plugins, marketplaces, and MCP servers.

→ Download page, always pointing at the latest release.

Built with Tauri. macOS 13 (Ventura) or later today, with Windows and Linux planned. Unsigned: no Apple Developer Program, no notarisation.

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For users

Claude Code keeps its skills, subagents, plugins, marketplaces, and MCP servers in config files and git clones scattered across your home folder. Fettlr reads the lot, at user level and per project, and hands you the buttons.

What it does

• Needs updating: one list of everything with an update waiting. Update an item on its own or run Update All.
• Skills: every skill Claude Code can load, with the description from its SKILL.md. Disable parks the skill's folder in Fettlr's own store so Claude Code cannot load it, and Enable puts it back untouched. Deleting moves the folder to the Trash, never rm -rf. Skills that came from a git clone can be pulled up to date in place.
• Subagents: every custom subagent from your user directory, your projects, and your plugins, with its model, tools, and permission mode; disable one without deleting it, or send it to the Trash.
• Plugins: install from any marketplace you have added, then enable, disable, update, or uninstall. Each plugin lists the skills and MCP servers it carries, and where it is installed.
• Marketplaces: add one by repo or URL, refresh the listings, and see which are behind their remote.
• MCP servers: user, project, and local scope side by side, plus the servers plugins provide. Add or edit one through a form instead of hand-writing JSON. Disabling a user-scope server keeps its full definition so enabling restores it exactly; project-scope servers use Claude Code's own enable and disable lists.
• Update tracking: marketplaces behind their remote, plugins on an older version than their marketplace offers, git-backed skills behind their upstream, and MCP servers whose pinned npm or PyPI package has a newer release. Checks run when Fettlr opens and, if you want, on an interval.
• Per project: filter skills, subagents, plugins, and MCP servers by project scope, next to your user-level setup.
• Find and jump: every list filters as you type (Cmd+F), and Cmd+K jumps straight to any skill, subagent, plugin, marketplace, or MCP server by name.
• Three languages: English (US and UK) and French, following your system language setting.
• Self-updating: Fettlr checks GitHub Releases for new versions and installs them in place, no drag-and-drop.

Screenshots

Coming once the first release ships.

Install

The app is unsigned, deliberately: no Apple Developer Program, no signing. macOS therefore blocks it on first launch. To allow it:

1. Open the downloaded DMG and drag Fettlr to your Applications folder.
2. Double-click Fettlr; when macOS warns it "can't verify the developer", click Done (not "Move to Trash"). Right-click the app and choose Open if your macOS version still offers that shortcut.
3. Open System Settings → Privacy & Security, scroll to the Security section, and click Open Anyway next to "Fettlr" was blocked to protect your Mac.
4. Authenticate and click Open.

macOS only asks once. After that it launches normally.

Using Claude Code? Point it at bootstrap/fettlr-launcher/SKILL.md and it installs and launches Fettlr for you, verifying the download against Fettlr's release key first.

Using it

1. Launch the app. Fettlr looks for the claude binary itself; if it cannot find it, point it at one in Settings.
2. Needs updating lists everything with an update waiting. Check for Updates re-runs the checks, Update All works through the list.
3. Skills, Plugins, Marketplaces, and MCP Servers each list what you have, filtered by scope, with the details and the actions in the panel that opens when you select a row.
4. Settings holds the path to the claude binary, how often to check for updates, and Fettlr's own update checks.

Every change is followed by a full re-read of the real state, so what Fettlr shows is what is on disk, not its own bookkeeping. Changes apply to new Claude Code sessions.

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For developers

Requirements

• Rust (stable) and Node.js with pnpm
• macOS: Xcode Command Line Tools (xcode-select --install)
• Tauri's own platform prerequisites; see the Tauri prerequisites guide

Build

pnpm install

# Core crate (no Tauri needed)
cargo test --workspace

# App: dev server with hot reload
pnpm tauri dev

# App: production bundle
pnpm tauri build

Gates

cargo test --workspace
cargo clippy --workspace --all-targets -- -D warnings
cargo fmt --check
pnpm run gate   # typecheck, lint, contrast check, localisation sync

All must pass before a commit.

App icon

swift scripts/make-icon.swift
pnpm --dir app tauri icon ../assets/icon-1024.png

The first command redraws assets/icon-1024.png, a 1024×1024 master, from assets/fettlr-glyph.svg and the fill constant at the top of the script. Deterministic, so re-running it changes nothing unless you change those constants. The second expands that master into every platform's icon set in app/src-tauri/icons/.

Localisation

Strings live in i18next JSON files under app/src/locales/. After adding or changing a user-facing string:

./scripts/sync-localizations.py          # sync keys, mirror en → en-GB
./scripts/sync-localizations.py --check  # fails if anything is untranslated

Architecture

fettlr/
├── crates/
│   └── fettlr-core/     Rust domain logic: CLI bridge, discovery, stores, updates, watcher.
│                          No Tauri dependency, fully tested independently.
├── app/
│   ├── src-tauri/         thin Tauri shell: typed IPC commands, events, the updater
│   └── src/                React + TypeScript frontend, view-only
├── packages/
│   └── design-system/     tokens, Tailwind theme, restyled shadcn components
├── site/                   Astro download site, imports the design system
├── scripts/                 icon generation, localisation sync/check
└── assets/                  source icon artwork

Key invariants:

• All domain logic lives in fettlr-core, independent of Tauri and fully tested; the app shell is a thin typed IPC layer, and the frontend is view-only.
• The core crate never resolves ~; every path that depends on your machine arrives injected via a Paths struct, so tests can point the whole crate at a temporary directory. The exceptions are four documented platform constants: /opt/homebrew/bin/claude and /usr/local/bin/claude, the well-known places Claude Code installs itself; /bin/zsh, the login shell used to find it when neither is there; and /usr/bin/git. They hold until the portability milestone.
• Secrets (MCP environment variables and header values) never leave the Tauri shell unmasked and never appear in logs.
• Contrast is enforced mechanically with APCA: packages/design-system/scripts/check-contrast.mjs checks every declared foreground-on-background pair against its Lc level, in both light and dark, on every run, with a ceiling on hairlines so a rule can never reach text weight.

For the full agent and contributor guide (conventions, invariants, build and test workflow), see AGENTS.md.

Licence

MIT. © 2026 Thomas Guillot.