Git commit-msg hook to verify commit message convention => https://datree.io/blog/git-commit-message-conventions-for-readable-git-log/

commit-msg-hook.py

#!/usr/bin/env python
"""
Git commit hook:
 .git/hooks/commit-msg
 Check commit message according to guidelines
"""

import sys
import re

REGEX = '' 
# e.g. ^(feat|fix|docs|style|refactor|test|build|ci|perf)(\(.+\))?\:\s(.{3,})

GUIDELINE_LINK = '<link to relvent commit mesage guideline>' 
# e.g. https://github.com/angular/angular/blob/master/CONTRIBUTING.md#commit

with open(sys.argv[1]) as commit:
    lines = commit.readlines()
    if len(lines) == 0:
        sys.stderr.write("\nEmpty commit message\n")
        sys.stderr.write("\n - Refer commit guide: {}\n\n".format(help_address))
        sys.exit(1)

    match_regex = re.match('({})'.format(REGEX), lines[0])

    if match_regex is None:
        sys.stderr.write("\nYour commit message subject line does not follow the guideline\n")
        sys.stderr.write("\n - Refer commit guideline: {}\n\n".format(GUIDELINE_LINK))
        sys.exit(1)

    sys.stderr.write("\nYour commit message looks good! \n\n")
sys.exit(0)

If you need more RegEx's, I have in my blog post the following best practices:

• Have a commit message
• Keep a short subject line
• Don’t end the subject line with a period
• Start with a capital letter
• Link to a planning system – Jira
• Angular Git commit message guidelines
• Emoji-Log commit message convention

Is it pre-commit or commit-msg hook?

You are right! I was using the wrong git hook name 😱
The right git hook is commit-msg so I updated the text accordingly.
Thank you for noticing :)