One of the side projects I’ve been working on lately is helping to shepherd the Semantic Versioning specification (SemVer) along to its 2.0.0 release. I want to thank everyone who sent pull requests and engaged in thoughtful, critical, spirited feedback about the spec. Your involvement has made it better!

I also want to thank Tom for creating SemVer in the first place and trusting me to help move it along.

I’ve mentioned SemVer in the past as it relates to NuGet. The 2.0.0 release of SemVer addresses some of the issues I raised.

What’s Changed?

Not too much has changed. Most of the changes focus around clarifications.

Build metadata

Perhaps the biggest change is the addition of optional build metadata (what we used to call a build number). This simply allows you to add a bit of metadata to a version in a manner that’s compliant with SemVer.

The metadata does not affect version precedence. It’s analogous to a code comment.

It’s useful for internal package feeds and for being able to tie a specific version to some mechanism that generated it.

For existing package managers that choose to be SemVer 2.0 compliant, the logic change needed is minimal. Instead of reporting an error when encountering a version with build metadata, all they need to do is ignore or strip the build metadata. That’s pretty much it.

Some package managers may choose to do more with it (for internal feeds for example) but that’s up to them.

Pre-release identifiers

Pre-release labels have a little more structure to them now. For example, they can be separated into identifiers using the “.” delimiter and identifiers that only contain digits are compared numerically instead of lexically. That way, 1.0.0-rc.1 < 1.0.0-rc.11 as you might expect. See the specification for full details.


The rest of the changes to the specification are concerned with clarifications and resolving ambiguities. For example, we clarified that leading zeroes are not allowed in the Major, Minor, or Patch version nor in pre-release identifiers that only contain digits. This makes a canonical form for a version possible.

If you find an ambiguity, feel free to report it.

What’s Next?

As SemVer matures, we expect the specification to become a little more formal in nature as a means of removing ambiguities. One such effort underway is to include a BNF grammar for the structure of a version number in the spec. This should hopefully be part of SemVer 2.1.