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Disable Mattermost's "Show More" with a 30-Line Plugin

· 2 min read

Mattermost truncates any post taller than 600 pixels, hiding the rest behind a "Show More" button with a gradient fade. There's no setting to turn this off — it's hardcoded in the webapp. If you're self-hosting and your posts are routinely long (AI bot responses, log dumps, code blocks), this gets old fast.

The fix is a tiny webapp-only plugin that injects CSS to remove the truncation.

Why there's no config for this​

The ShowMore React component checks rendered post height against a hardcoded 600px constant. If it's taller, the post gets the post-message--collapsed class, a max-height: 600px on the text container, a gradient mask, and the "Show More" button. The server has no opinion about this — it's purely client-side.

There's no config toggle or feature request on the roadmap. So we'll do it ourselves.

The plugin​

Mattermost's plugin system supports webapp-only plugins — a JSON manifest and a JS bundle that runs in the browser. No server component needed. The plugin's initialize function appends a <style> tag to <head> that overrides the collapsed post styles: removes the max-height: 600px cap, kills the gradient fade mask, and hides the "Show More" button.

The source and a pre-built .tar.gz are in this gist — download and install, no building required.

Install​

Via System Console​

  1. Download com.boehs.no-show-more.tar.gz from the gist
  2. Go to System Console > Plugin Management
  3. Upload the .tar.gz and click Enable

Plugin uploads must be enabled (PluginSettings.EnableUploads: true in config.json).

Via mmctl (Docker)​

docker cp com.boehs.no-show-more.tar.gz mattermost:/tmp/
docker exec mattermost mmctl --local plugin add /tmp/com.boehs.no-show-more.tar.gz
docker exec mattermost mmctl --local plugin enable com.boehs.no-show-more

This requires ServiceSettings.EnableLocalMode: true in config.json. Restart Mattermost after changing config.

Notes​

  • Hard-refresh the browser (Cmd+Shift+R) or restart the desktop app after installing — the CSS loads at page init.
  • Survives updates — plugins installed via the API are persisted in Mattermost's filestore. They survive container restarts and image upgrades.
  • Tested on Mattermost 11.3.0. The CSS class names have been stable for years, but if a future version changes them, inspect the page and update the selectors in main.js.

This post was generated with EARL (via Opus 4.6), but reviewed by me.