A fast, native macOS client for your existing Mattermost servers.
100% Swift, built with SwiftUI and AppKit. No Electron and no web view.
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Note
MatterMac is an independent project, not an official Mattermost application. It is under active development: nightly builds are published every day, and there is no production release yet.
Markdown, tables, task lists, code blocks, quotes, emoji and attachment cards are all rendered natively, and threads open in a pane beside the channel. Reactions, edits, pinned and saved messages, unread lines and mentions work the way you expect from Mattermost.
Press ⌘ K to switch to any channel, direct message or person. Results are ranked by how well they match, unread conversations come first, and matching ignores accents. Server-wide message and file search is built in.
| Quick switcher | Search |
|---|---|
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Images open in an in-window viewer with zoom, keyboard navigation, copy and save. Channel Info collects the purpose, header, members, pinned messages, files and per-channel settings.
| Media viewer | Channel Info |
|---|---|
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Pick a window theme, or mix your own gradient from two to four colours. Themes tint the sidebar, conversation and Liquid Glass chrome, in light and dark mode. MatterMac reduces any tint that would make text hard to read.
| Dusk | Lagoon | Ember |
|---|---|---|
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Sign in with a password (including MFA), a personal access token, or browser-based SSO. Several servers can stay signed in at once, and sign-ins are restored from the macOS Keychain at launch.
- Native and light. A SwiftUI shell with an AppKit timeline and composer. Memory, tasks and caches are all bounded by one resource budget.
- Fast to open. An encrypted on-device cache shows your channels, profiles, images and recent messages at once, then refreshes them from the server.
- Liquid Glass on macOS 26 and later, with material fallbacks on macOS 14 and 15.
- Everyday essentials: file uploads and downloads, pasted images, custom emoji with completion, slash-command suggestions, and editing your profile and status.
- Mac integration: notifications with message previews (on by default), automatic online and away status, keyboard shortcuts for navigation, and a Dock badge.
- Nothing lost silently. Review Unsent Work lets you copy drafts or unconfirmed sends and export pasted images before you discard them.
- Keeps itself up to date from GitHub releases, on the Stable or Nightly channel.
- Download the latest DMG from Releases. Every build is signed with a Developer ID and notarized by Apple.
- Open it and drag MatterMac to Applications.
- Enter your server address and choose Continue. Check the address MatterMac will connect to, choose Connect, then sign in. Release builds require HTTPS.
MatterMac checks GitHub for updates at launch and every six hours, verifies what it downloads, and offers Restart to Update. Choose the channel in Settings ▸ General ▸ Updates.
You need Xcode 27 (Swift 6.4). The app runs on macOS 14 or later, though
macOS 14 and Intel Macs have not been verified yet. Open MatterMac.xcworkspace
and run the MatterMac scheme, or use these commands from the repository root:
swift test --package-path Packages/MatterMacKit
xcodebuild -workspace MatterMac.xcworkspace -scheme MatterMac \
-configuration Debug -derivedDataPath build build
open build/Build/Products/Debug/MatterMac.app- Local test servers: Debug builds accept
-MatterMacAllowInsecureLoopback YES. The Docker setup is in CONTRIBUTING.md. - No Developer ID certificate? See releasing for the ad-hoc signing override.
- Releases: the nightly and production pipelines, versions, in-app updates and secrets are all documented in docs/releasing.md.
MatterMac talks only to your Mattermost servers, plus GitHub to check for updates. It never sends account or message data to GitHub.
| What | Where | Details |
|---|---|---|
| Sign-ins | macOS Keychain | Bearer token and kind, server address and account ID. Passwords are never saved. |
| Content cache | Sandbox Caches, encrypted | Images, profiles, the channel list and recent messages. Encrypted with a per-account key kept in Keychain, capped at 512 MiB of images and 96 MiB of other content, and excluded from backups. Cached messages never mark a channel read. |
| Settings | MatterMac's preferences | The "On This Mac" values: notifications, previews, sound, Dock bounce, send behavior, text size, appearance and theme. |
| Drafts | Memory only | Drafts, pending sends and pasted images stay in bounded memory. They do not survive quit, a crash, or forced termination. |
Quitting keeps sign-ins and the cache; Sign Out removes that account's sign-in, cache and key. Settings ▸ Accounts shows the cache size and has Clear Cache.
- Limits: drafts and pending sends share a budget of 100 items or 4 MiB of text, and pasted images share 8 MiB. At the limit MatterMac refuses new work rather than evicting unsent work.
- Uploads start when you send; files can stay on the server if their message is never posted.
- Downloads and exports are written only when you choose to.
- Outside the app's control: macOS swap, system diagnostics and other apps. A full filesystem audit has not run yet.
Tested server versions. Live tests cover REST and WebSocket messaging, and the native conversation and attachment flows, on Mattermost 10.11.24, 11.11.1, and 11.11.1 under a URL subpath.
- Both peers in these tests are native clients.
- A separate real-app check exchanged channel and DM messages both ways with the official web client on 11.11.1, including after relaunch and sign-in again.
- Browser SSO supports the routes a server advertises, but each identity provider still needs testing on a real deployment.
See compatibility and the dated verification record.
Out of scope: Calls, arbitrary web plugins, Boards, Playbooks dashboards and administration. Interactive command dialogs and ephemeral bot posts are not supported yet.
Still open:
- Accessibility, real input methods (IMEs), running on the minimum macOS version, privacy audits and full performance gates are incomplete.
- Synthetic rendering measurements are in benchmarks.
- A two-hour soak found a row-retention defect. It is fixed and covered by a regression test that failed before the fix, but still needs a sustained foreground remeasurement.
Screenshots show synthetic people and content, generated entirely in process by an opt-in test (see asset provenance).
- CONTRIBUTING.md: local servers, opt-in tests and review expectations.
- Architecture: how the code is organised.
- SECURITY.md: how to report security issues.
Please keep credentials and private server content out of public reports.
Licensed under the MIT License.