diff --git a/.github/workflows/completion.yml b/.github/workflows/completion.yml
new file mode 100644
index 0000000..e3de9b6
--- /dev/null
+++ b/.github/workflows/completion.yml
@@ -0,0 +1,34 @@
+name: completion
+
+# The completion scripts run inside shells no unit test starts: check each one for real.
+on:
+  pull_request:
+    paths: ['src/completion.ts', 'src/cli.tsx', 'scripts/check-completion.sh', '.github/workflows/completion.yml']
+  push:
+    branches: [main]
+    paths: ['src/completion.ts', 'src/cli.tsx', 'scripts/check-completion.sh', '.github/workflows/completion.yml']
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+jobs:
+  shells:
+    runs-on: ubuntu-latest
+    timeout-minutes: 10
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-node@v4
+        with:
+          node-version: 22
+          cache: npm
+      # bash and PowerShell come with the runner image.
+      - run: sudo apt-get update -q && sudo apt-get install -y -q zsh fish
+      - run: npm ci && npm run build && npm link
+      - name: Shell versions
+        run: |
+          bash --version | head -1
+          zsh --version
+          fish --version
+          pwsh -NoProfile -Command '$PSVersionTable.PSVersion.ToString()'
+      - run: bash scripts/check-completion.sh
diff --git a/scripts/check-completion.sh b/scripts/check-completion.sh
new file mode 100755
index 0000000..8ecc6a5
--- /dev/null
+++ b/scripts/check-completion.sh
@@ -0,0 +1,45 @@
+#!/usr/bin/env bash
+# Checks the shell completion scripts: syntax, then a real completion in each shell.
+# Needs skills-atlas on PATH (npm run build && npm link) and bash, zsh, fish, pwsh.
+# Usage: scripts/check-completion.sh [shell...]   (default: all four)
+set -u
+dir=$(mktemp -d)
+failed=0
+pass() { echo "ok   $1"; }
+fail() { echo "FAIL $1"; failed=1; }
+# `skills-atlas ins` must offer `install`.
+expect_install() { grep -qx 'install' && pass "$1" || fail "$1"; }
+
+for shell in "${@:-bash zsh fish powershell}"; do
+  for sh in $shell; do
+    file="$dir/completion.$sh"
+    skills-atlas completion "$sh" > "$file" || { fail "$sh: script not generated"; continue; }
+    case "$sh" in
+      bash)
+        bash -n "$file" && pass "bash: syntax" || fail "bash: syntax"
+        bash -c "source '$file'; COMP_LINE='skills-atlas ins'; COMP_POINT=\${#COMP_LINE}; _skills_atlas; printf '%s\n' \"\${COMPREPLY[@]}\"" \
+          | expect_install "bash: completes 'skills-atlas ins'"
+        ;;
+      zsh)
+        zsh -n "$file" && pass "zsh: syntax" || fail "zsh: syntax"
+        # compdef and compadd belong to the completion system: stand-ins print what would be offered.
+        zsh -c "compdef() { :; }; compadd() { [[ \$1 == -- ]] && shift; print -l -- \"\$@\"; }; source '$file'; words=(skills-atlas ins); CURRENT=2; _skills_atlas" \
+          | expect_install "zsh: completes 'skills-atlas ins'"
+        ;;
+      fish)
+        fish -n "$file" && pass "fish: syntax" || fail "fish: syntax"
+        fish -c "source '$file'; complete -C 'skills-atlas ins'" | cut -f1 \
+          | expect_install "fish: completes 'skills-atlas ins'"
+        ;;
+      powershell)
+        pwsh -NoProfile -Command "\$e = \$null; [void][System.Management.Automation.Language.Parser]::ParseFile('$file', [ref]\$null, [ref]\$e); if (\$e.Count) { \$e; exit 1 }" \
+          && pass "powershell: syntax" || fail "powershell: syntax"
+        pwsh -NoProfile -Command ". '$file'; (TabExpansion2 -inputScript 'skills-atlas ins' -cursorColumn 16).CompletionMatches | ForEach-Object CompletionText" \
+          | tr -d '\r' | expect_install "powershell: completes 'skills-atlas ins'"
+        ;;
+      *) fail "$sh: unknown shell" ;;
+    esac
+  done
+done
+rm -rf "$dir"
+exit $failed