• Why my git tags cannot be pushed sometimes?
• What’s the difference between git push --follow-tags and git push --tag?

There are concepts beneath the questions. Firstly, We will talk about lightweight tag and annotated tag.

Lightweight Tag And Annotated Tag.

Quote from Git - Tagging

Git supports two types of tags: lightweight and annotated.

A lightweight tag is very much like a branch that doesn’t change — it’s just a pointer to a specific commit.

Annotated tags, however, are stored as full objects in the Git database. They’re checksummed; contain the tagger name, email, and date; have a tagging message; and can be signed and verified with GNU Privacy Guard (GPG). It’s generally recommended that you create annotated tags so you can have all this information; but if you want a temporary tag or for some reason don’t want to keep the other information, lightweight tags are available too.

As we can see, annotated tags are the tags that matter. They should be taking good care of.

How To Tag?

git tag <tagname>                 => lightweight tag
git tag -a <tagname>              => annotated tag, will prompt for mesage
git tag -a -m <msg> <tagname>     => annotated tag
git tag -m <msg> <tagname>        => annotated tag

What Does npm version Do?

npm version will tag package versions like this:

Quote from cli/version.js · npm/cli

// ...
const flagForTag = signTag ? '-sm' : '-m'
// ...
stagePackageFiles(localData, options).then(() => {
  return git.exec(commitArgs, options)
}).then(() => {
  if (!localData.existingTag) {
    return git.exec([
      'tag', npm.config.get('tag-version-prefix') + version,
      flagForTag, message
    ], options)
  }
}).nodeify(cb)
// ...

It is an annotated tag.

So How Do We Push Tags?

There are two ways of pushing tags:

• git push --follow-tags
• git push --tags

Quote from How do you push a tag to a remote repository using Git? - Stack Overflow

git push --follow-tags

It pushes both commits and only tags that are both:

• annotated
• reachable (an ancestor) from the pushed commits

This is sane because:

• you should only push annotated tags to the remote, and keep lightweight tags for local development to avoid tag clashes. See also: What is the difference between an annotated and unannotated tag?
• it won’t push annotated tags on unrelated branches

It is for those reasons that –tags should be avoided.

How do we push tags? git push --follow-tags!

In Conclusion

When you can’t push tags, you probably:

• are using a lightweight tag, and git push --follow-tags.

While you can push tags, you probably:

• are using a lightweight tag, and git push --tags. (Not recommended!)
• are using an annotated tag, and git push --follow-tags.

Reference

• How do you push a tag to a remote repository using Git? - Stack Overflow
• Git - Tagging
• cli/version.js · npm/cli
• Git - git-push Documentation