Use Semantic Versioning and Give Your Version Numbers Meaning

It's pretty amazing that in 2017 I still find plenty of projects with no versioning, a random version scheme, or stuck perpetually at 0.1.x. Figuring out the maturity of these projects or the scope of changes between two versions can be terribly difficult. Versioning without any guidelines produces meaningless versions, so we need to follow common guidelines that can make our version numbers meaningful.

Luckily, we have a standard for versioning our software that works quite well: Semantic Versioning (SemVer for short). You've probably seen the SemVer "triple" (e.g. 2.7.0) in your software journeys.

SemVer can be summarized quite simply. Your version is composed of three components: MAJOR.MINOR.PATCH.

There are simple rules that indicate when you must increment each of these versions:

  • MAJOR is incremented when you make breaking API changes
  • MINOR is incremented when you add new functionality without breaking the existing API or functionality
  • PATCH is incremented when you make backwards-compatible bug fixes

Getting Started with SemVer

Semantic Versioning is not complicated, and you can get started by following a small number of guidelines:

  1. New projects start at version 0.1.0
    • You are starting with a set of features, not bug fixes
    • Increment the minor version for each subsequent release
  2. Start versioning at 1.0.0 if:
    • Your software is already used in production
    • Other users depend on your software and care when the API changes
    • You are worrying about backwards compatibility
  3. The initial development phase is represented by MAJOR version 0
    • Make as many breaking changes as you want before v1.0.0
  4. Once you have released v1.0.0, API adjustments or other breaking changes are not acceptable without a new MAJOR version change
  5. If you are adding new features without breaking the existing API or functionality, increment the MINOR number.
  6. If you are fixing bugs, increment the PATCH number.
  7. Avoid making frequent breaking changes unless you absolutely need to!
    • Batch major changes together on a branch until you have enough to justify a new major release

Note well: Keeping a system that's in production or being heavily used at a pre-1.0.0 version is a bad practice. You might as well not be using SemVer at all.

But what if I need additional labels, like "alpha"?

It's pretty common to want to add labels to our builds, to indicate something like a pre-release, alpha, or beta software version.

Semantic versioning supports labels and build metadata as an extension to the MAJOR.MINOR.PATCH format. Simply add a hyphen and identifier to the version number.

For example, say you have a version 1.0.0 candidate ready but want to test it before you make your release. You could label the pre-release versions as follows:

1.0.0-alpha.1
1.0.0-alpha.2

Once you are happy with the stability of 1.0.0, you can make the official release and drop the alpha.x label.

The Semantic Versioning Specification

The Semantic Versioning web page contains the complete specification and answers common questions, so I recommend taking a few minutes to read through it.

Since you're already here, I've included v2.0.0 of the SemVer specification:

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as described in RFC 2119.

  1. Software using Semantic Versioning MUST declare a public API. This API could be declared in the code itself or exist strictly in documentation. However it is done, it should be precise and comprehensive.

  2. A normal version number MUST take the form X.Y.Z where X, Y, and Z are non-negative integers, and MUST NOT contain leading zeroes. X is the major version, Y is the minor version, and Z is the patch version. Each element MUST increase numerically. For instance: 1.9.0 -> 1.10.0 -> 1.11.0.

  3. Once a versioned package has been released, the contents of that version MUST NOT be modified. Any modifications MUST be released as a new version.

  4. Major version zero (0.y.z) is for initial development. Anything may change at any time. The public API should not be considered stable.

  5. Version 1.0.0 defines the public API. The way in which the version number is incremented after this release is dependent on this public API and how it changes.

  6. Patch version Z (x.y.Z | x > 0) MUST be incremented if only backwards compatible bug fixes are introduced. A bug fix is defined as an internal change that fixes incorrect behavior.

  7. Minor version Y (x.Y.z | x > 0) MUST be incremented if new, backwards compatible functionality is introduced to the public API. It MUST be incremented if any public API functionality is marked as deprecated. It MAY be incremented if substantial new functionality or improvements are introduced within the private code. It MAY include patch level changes. Patch version MUST be reset to 0 when minor version is incremented.

  8. Major version X (X.y.z | X > 0) MUST be incremented if any backwards incompatible changes are introduced to the public API. It MAY include minor and patch level changes. Patch and minor version MUST be reset to 0 when major version is incremented.

  9. A pre-release version MAY be denoted by appending a hyphen and a series of dot separated identifiers immediately following the patch version. Identifiers MUST comprise only ASCII alphanumerics and hyphen [0-9A-Za-z-]. Identifiers MUST NOT be empty. Numeric identifiers MUST NOT include leading zeroes. Pre-release versions have a lower precedence than the associated normal version. A pre-release version indicates that the version is unstable and might not satisfy the intended compatibility requirements as denoted by its associated normal version. Examples: 1.0.0-alpha, 1.0.0-alpha.1, 1.0.0-0.3.7, 1.0.0-x.7.z.92.

  10. Build metadata MAY be denoted by appending a plus sign and a series of dot separated identifiers immediately following the patch or pre-release version. Identifiers MUST comprise only ASCII alphanumerics and hyphen [0-9A-Za-z-]. Identifiers MUST NOT be empty. Build metadata SHOULD be ignored when determining version precedence. Thus two versions that differ only in the build metadata, have the same precedence. Examples: 1.0.0-alpha+001, 1.0.0+20130313144700, 1.0.0-beta+exp.sha.5114f85.

  11. Precedence refers to how versions are compared to each other when ordered. Precedence MUST be calculated by separating the version into major, minor, patch and pre-release identifiers in that order (Build metadata does not figure into precedence). Precedence is determined by the first difference when comparing each of these identifiers from left to right as follows: Major, minor, and patch versions are always compared numerically. Example: 1.0.0 < 2.0.0 < 2.1.0 < 2.1.1. When major, minor, and patch are equal, a pre-release version has lower precedence than a normal version. Example: 1.0.0-alpha < 1.0.0. Precedence for two pre-release versions with the same major, minor, and patch version MUST be determined by comparing each dot separated identifier from left to right until a difference is found as follows: identifiers consisting of only digits are compared numerically and identifiers with letters or hyphens are compared lexically in ASCII sort order. Numeric identifiers always have lower precedence than non-numeric identifiers. A larger set of pre-release fields has a higher precedence than a smaller set, if all of the preceding identifiers are equal. Example: 1.0.0-alpha < 1.0.0-alpha.1 < 1.0.0-alpha.beta < 1.0.0-beta < 1.0.0-beta.2 < 1.0.0-beta.11 < 1.0.0-rc.1 < 1.0.0.

Further Reading