---
 app.go         |  1 +
 completions.go | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/app.go b/app.go
index 1144560..4706536 100644
--- a/app.go
+++ b/app.go
@@ -938,6 +938,7 @@ func (app *App) completions(cursorIdx int, text []rune) []ui.Completion {
 		cs = app.completionsChannelMembers(cs, cursorIdx, text)
 	}
 	cs = app.completionsMsg(cs, cursorIdx, text)
+	cs = app.completionsCommands(cs, cursorIdx, text)
 
 	if cs != nil {
 		cs = append(cs, ui.Completion{
diff --git a/completions.go b/completions.go
index 3e4a516..6f99a60 100644
--- a/completions.go
+++ b/completions.go
@@ -99,6 +99,26 @@ func (app *App) completionsMsg(cs []ui.Completion, cursorIdx int, text []rune) [
 	return cs
 }
 
+func (app *App) completionsCommands(cs []ui.Completion, cursorIdx int, text []rune) []ui.Completion {
+	if !hasPrefix(text, []rune("/")) {
+		return cs
+	}
+	uText := strings.ToUpper(string(text[1:]))
+	for name, _ := range commands {
+		if strings.HasPrefix(name, uText) {
+			c := make([]rune, 1+len(name))
+			copy(c[:1], []rune("/"))
+			copy(c[1:], []rune(name))
+
+			cs = append(cs, ui.Completion{
+				Text:      c,
+				CursorIdx: 1 + len(name),
+			})
+		}
+	}
+	return cs
+}
+
 func hasPrefix(s, prefix []rune) bool {
 	return len(prefix) <= len(s) && equal(prefix, s[:len(prefix)])
 }
-- 
2.34.1

Thanks for the patch. It works well, just an edge case that needs to be 
handled:

1. type "/m #channel +b"
2. place cursor after "/m"
3. press tab

You'll need to take the first word of "text" only, and append the rest 
of "text" to each completion.