A terminal client for the Mattermost chat system
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This release supports server version 4.4.

New features:

  • The active color theme can be customized by creating a theme customization file and setting the new themeCustomizationFile option. This setting lets you override any foreground color, background color, or style of any aspect of the Matterhorn interface. For details on the format of the customization file, please see the “Themes” help in Matterhorn with the /help themes command.
  • Edited posts are now displayed with a trailling “edited” marker. This change includes some new behavior and a new configuration option:
    • When you visit a post that has recent edits, the “edited” marker will be highlighted. This highlight can be dismissed in the same way as the “New Messages” cutoff, using the M-l keybinding.
    • This feature can be turned off using by setting the showOlderEdits configuration option to False.
  • New commands:
    • The /remove-user command removes a user from a channel.
    • The /group-msg command creates a new private group channel including several users.
    • The /search [term] command searches the chat history for posts that include the provided text and displays those posts in an overlay. Thanks to @abhin4v for this change!
  • Matterhorn now includes embedded hyperlinks using terminal escape sequences in terminals that support them. For more information on terminal support for hyperlink escape sequences, please see this gist and its associated discussion.
  • The width of the channel list (in columns) is now configurable with channelListWidth, which defaults to 20.
  • The urlOpenCommand can now be an interactive terminal-based program (such as a terminal-based web browser) but this requires the configuration option urlOpenCommandIsInteractive to be set to True. This defaults to False and should not be changed if the urlOpenCommand is not a terminal-based program.
  • The current selection in channel select mode can be moved forward and backward with C-n and C-p. (fixes #139)
  • Quotation blocks now include visible characters in addition to indentation.
  • We now honor the server’s notification settings for channels.

Bug fixes:

  • New direct-message channels are properly added to running sessions (fixes #264)
  • No more reporting of “resource vanished” exceptions (fixes #116)
  • Missing editing keybindings now included in edit binding list (fixes #139)
  • Websocket message parse failures no longer result in crashes (fixes


  • The sidebar no longer shows deleted users (fixes #316)

  • Tab-completion no longer includes deleted users (fixes #320)

  • User status updates are now rate-limited (fixes #282)

  • Private channels can be deleted successfully (fixes #304)

  • External commands now run in the background in their own thread and do not block the main UI (fixes #270)

  • Channel renaming is honored at runtime and does not require a restart (fixes #324)

  • Group channel show/hide preferences are observed, which in practice means a user can now ‘leave’ a several-user group channel

  • New channels will not appear twice in the sidebar (fixes #327)

  • New messages to previously-hidden group channels will cause the group channel to be shown again (fixes #326)

Package changes:

  • PRACTICES.md is now listed in extra-doc-files.
  • Three scripts usable with the /sh command are now listed in extra-doc-files:
    • cowsay runs the message text through the cowsay shell command and formats the output as a verbatim block. This command requires the cowsay command-line program to be installed externally.
    • figlet runs the message text through the figlet shell command and formats the output as a verbatim block. This command requires the figlet command-line program to be installed externally.
    • rot13 runs the trivial ROT13 subsitution cipher over the message text and otherwise passes it through unchanged.


New features:

  • Messages that start with a block-level element now get laid out so that the block level element appears underneath, rather than to the right of, the user name. This helps with long usernames such as bots. Thanks to @kellymclaughlin for this change.
  • Code blocks with fencing now display the language when syntax highlighting is active.
  • In channel scroll mode, Up/Down arrow keys scroll by just one row
  • All channel and user data are now fetched more efficiently on startup for greatly improved startup time.

Bug fixes:

  • The /members command now only shows active users (fixes #315)
  • Reset edit mode after handling commands and message input, provide reply context when running commands (fixes #305)
  • Allow all unknown client commands to fall through to server (fixes


  • Improve uniqueness comparisons for URL lists


Bug fixes:

  • Attachments no longer appear in duplicate for edited messages.

Package changes:

  • CHANGELOG.md is now listed in extra-doc-files.


Package changes:

  • Upgraded mattermost-api to 40000.0.1.
  • Upgraded mattermost-api-qc to 40000.0.1.

Bug fixes:

  • Ignore emoji_added websocket events rather than crashing due to JSON decode failures (#296)
  • channel_viewed websocket events from 4.0 servers lacking a channel_id value no longer cause a client crash (https://mattermost.atlassian.net/browse/PLT-7252)
  • mkrelease.sh: use correct bindist file extension (#295)


This release supports server version 4.0.

Package changes:

  • Upgraded mattermost-api to 40000.0.0.
  • Upgraded mattermost-api-qc to 40000.0.0.

Bug fixes:

  • Attempts to /focus your own DM channel no longer trigger a server error (fixes #294)
  • Message edits now properly restore message reactions and attachments (fixes #292)
  • DM channels with topics now display those topics in addition to the DM channel user identification.
  • Rendering of attachments regressed in 31000.0.0 and is now fixed so that attachments are displayed beneath, not to the right of, their messages.

New features:

  • Markdown image alt text is now rendered when available and Markdown images are now available in the C-o URL list (fixes #285)
  • Added a new configuration setting, showBackgroundActivity, which determines whether the status of Matterhorn’s asynchronous work queue is displayed in the interface. This setting is mostly for developers but can be a helpful diagnostic tool. When enabled, the setting causes the async queue length to appear in the lower-right corner of the interface.
  • Added a new configuration setting, unsafeUseUnauthenticatedConnection, which causes Matterhorn to use a non-HTTPS connection when connecting to the configured host and port. As the sample configuration file says, use this only if you know what you are doing.

Internal changes:

  • Added support for 4.0’s channel_viewed and channel_updated websocket events.


This release supports server version 3.10.0.

Package changes:

  • Upgraded mattermost-api to 31000.0.0.
  • Upgraded mattermost-api-qc to 31000.0.0.

New features and keybindings:

  • Matterhorn now supports Flagged Posts. To use this feature:
    • Press M-8 or use the /flags command to show a list of your flagged posts. Within that view, ‘f’ will unflag a selected message.
    • In message selection mode in channels (C-s), ‘f’ will flag/unflag the selected message.
    • Flagged posts appear with a flag marker “[!]” next to the author’s username.
  • Syntax highlighting of fenced code blocks is now supported in 256-color terminals. Code blocks must provide the langauge hint using the same syntax as supported by the web client.
  • Spell checking of user input is now supported using Aspell. To use this feature:
    • Install the Aspell binary and dictionaries on your system.
    • Set enableAspell = true in your Matterhorn configuration.
    • Optionally, set aspellDictionary to the name of the Aspell dictionary you want to use (this is only necessary if you want to override your LANG setting, which is typically sufficient)
    • Once user input is entered into the input area, a short delay after typing stops, a spell check will highlight any misspelled words.
  • Home and End now move the cursor as usual in editor while in normal mode, and also navigate the message list while scrolling.
  • Matterhorn now displays the mention count in the channel sidebar to mimic the web client behavior and highlights channels with at least one mention in magenta in the sidebar.

Bug fixes and improvements:

  • Configuration file values can now use quoted string syntax (fixes


  • The channel switch mode prompt now mentions anchors.

  • The URL opening command is now run asynchronously.

  • Input history files are now saved with an appropriate file mode (fixes #218)

  • Fixed a bug that caused users created after a session began not to appear in the sidebar.

  • Help topics (valid arguments to /help) are now displayed in the main help UI (fixes #225)

  • Message deletion now also deletes replies to the deleted message (fixes #257)

  • On channel deletion, leave before deleting to avoid a server error.

  • URLs in the URL list are now displayed in the same order in which they appear in messages (fixes #250)

  • User identification now appears in DM channel headers.

  • Numbered lists now render starting at first specified number (fixes


  • The login screen now displays validation errors for hostname and port inputs when appropriate (fixes #242)

  • Channel select inputs that have an exact match no longer require ^/$ anchors.


This release supports server version 3.8.2. This release is our first official public release.

Package changes:

  • Removed stale array and data-default dependencies
  • Increased lower bound on base dependency to 4.8 to relect our GHC testing.


  • Subprocess error logs are now only created on demand. Previously we created them on startup before any subprocess errors had occurred.
  • We now provide a QuickCheck test for some infrastructure.

Bug fixes:

  • Fixed a bug whereby some resize operations would cause a program crash by triggering an unsafe mutable vector operation in Vty.
  • New user creation is now handled successfully and no longer requires a client restart to function reliably. Previously bad behavior included not coloring new users’ names and not showing new users’ names at all on their messages.
  • Message selection mode is no longer blocked by errors and other non-post content.
  • Subprocesses that fail to run are now consistently mentioned in the subprocess error log.


This release supports server version 3.8.2.

Package changes:

  • Relax constraint on containers to allow 0.5.7 or greater.
  • Upgraded mattermost-api to 30802.0.0.

Bug fixes:

  • The help interface now updates properly when showing either the main help window or the scripts help window.
  • Attachments are now saved asynchronously.
  • Attachments are now opened without using the browser, thus removing our dependency on a valid browser session with the server (fixes #128)
  • Editing state is now saved before switching history entries (fixes


  • Messages with unknown authors trigger a user metadata fetch (fixes #205)

New keybindings:

  • C-o now opens the URL list while scrolling through channel messages.
  • C-c now cancels channel selection in C-g mode

UI changes:

  • Channel scroll mode keybindings were added to the help page.
  • We no longer perform string highlighting on the contents of Markdown code spans in messages.
  • On startup, only the scrollback for Town Square is fetched to improve performance. Scrollback for other channels is fetched on demand.
  • We now use the channel sigil “~” rather than “#” to match the web client behavior, and highlight ~-prefixed channel names (fixes #204).


This release supports server version 3.7.1.

New features:

  • Matterhorn now has basic support for 3.7’s new “group channel” feature. If other users add you to a group channel, it will appear in the sidebar with the member usernames listed (e.g. “#bob, sue, …”). Creation of group channels will be supported in a future release.
  • When the urlOpenCommand program produces output on standard output or standard error, this output is now logged and a message is posted in the current channel with the path to the log file. This feature prevents the URL open command from poisoning the terminal state with unexpected output.
  • Added a /members command to show current channel membership.
  • Channel header changes from other users will now cause the channel topic string to update.
  • Added a /delete-channel command to delete the current channel.
  • Markdown rendering now puts empty lines between adjacent block elements of the same variety to improve readability.

Bug fixes:

  • Message selection now only supports reply/edit/delete on normal posts (fixes #174)
  • C-n/p now only change channels when a non-DM channel is selected (fixes #82)
  • We now handle new user events (fixed #111)
  • On channel change we now always reset the channel list to scroll to the top (fixes #138)
  • When a draft message is left in the editor when changing channels, a new sigil (“»”) appears for the previous channel instead of the usual “#” to indicate this.
  • The help interface now resizes properly all the time.

Performance improvements:

  • On startup, all channel contents are fetched asynchronously. Town Square fetches are prioritized. These changes drastically improve startup time, even on fast connections.

Documentation changes:

  • The README now includes a feature list, a brief feature overview for new users, and a section on how to contribute.

Package changes:

  • Upgraded mattermost-api to 30701.0.0.
  • Binary releases now include the copyright and licensing information for all dependencies.

Internal changes:

  • Added preemption support for asynchronous work queue processing. doAsync(With) now both take an AsyncPriority.


New editing keybindings:

  • C-w, M-Backspace now delete the word to the left of the cursor.
  • M-d deletes the word to the right of the cursor.
  • C-k now kills text from the cursor to the end of the line and copies to an internal buffer; C-y pastes from said buffer.
  • C-b, C-f move back and forward by one word, respectively.

  • Many editing keybindings are now present in their own Help page section.

Package changes:

  • Upgraded text-zipper to 0.10.
  • Upgraded mattermost-api to 30600.2.2.


Bug fixes:

  • Message-yanking failures due to missing programs (e.g. xclip) no longer trigger an unhandled exception (fixes #170)
  • Users that are not members of the current team are now hidden from the user list (fixes #161)
  • User statuses in the sidebar are now periodically refreshed
  • Supported server commands now appear on the help screen (fixes #162)
  • Files containing non-UTF-8 content no longer trigger unhandled exceptions when being read by matterhorn (fixes #168)
  • Updated repository URL in error message about reporting problems (thanks @tommd)


  • Improved formatting of message attachments so that their filenames are shown. Previously only their hash identifiers were displayed. This change also entails asynchronous fetching of attachment metadata.
  • Upgraded to mattermost-api 30600.2.1.


  • Fixed a bug that caused message selection mode to trigger a Vty crash when a message being rendered was larger than half of the area available for the message list.


  • Added a new message selection mode. This mode provides access to four new features: replies, edits, deletion, and verbatim text yanking. To enter this mode, use the default binding of C-s (and cancel with Esc). The resulting cursor can be used to select messages in the current channel and perform the following actions on them:

    • y: for messages with any verbatim text, yank the verbatim text to the first verbatim block in the message to the system clipboard (works on Linux and OSX)
    • r: reply to the selected message. To cancel a reply, press C-c or Esc.
    • e: for messages written by the current user, edit the selected message. To cancel an edit, press C-c or Esc.
    • d: for messages written by the current user, delete the selected message (with a confirmation).
    • o: for messages containing URLs, open all URLs in the selected message.
    • j/k/up/down/pgup/pgdown: change the selected message cursor position.
  • Added a C-r binding to begin a reply to the most recently posted message in the current channel.

  • M-e now toggles multiline editing mode rather than just enabling it. Previously, Esc toggled it off.

  • Upgraded to mattermost-api 30600.2.0.


  • Upgraded to mattermost-api 30600.1.0. This fixed /me and /shrug server-side command execution failures.


Initial versioned release for server version 3.6.0.