Additional labels for pre-release and build metadata are available as extensions to the MAJOR.

In systems with many dependencies, releasing new package versions can quickly become a nightmare. If the dependency specifications are too tight, you are in danger of version lock the inability to upgrade a package without having to release new versions of every dependent package.

If dependencies are specified too loosely, you will inevitably be bitten by version promiscuity assuming compatibility with more future versions than is reasonable. As a solution to this problem, I propose a simple set of rules and requirements that dictate how version numbers are assigned and incremented. These rules are based on but not necessarily limited to pre-existing widespread common practices in use in both closed and open-source software. For this system to work, you first need to declare a public API.

This may consist of documentation or be enforced by the code itself. Regardless, it is important that this API be clear and precise. Once you identify your public API, you communicate changes to it with specific increments to your version number. Consider a version format of X. Software using Semantic Versioning MUST declare a public API. This API could be declared in the code itself or exist strictly in documentation.

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However it is done, it should be precise and comprehensive. A normal version number MUST take the form X. 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.

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. Major version zero 0. Anything may change at any time.

The public API should not be considered stable. The way in which the version number is incremented after this release is dependent on this public API and how it changes. Patch version Z x. A bug fix is defined as an internal change that fixes incorrect behavior. Minor version Y x.

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. Major version X X. It MAY include minor and patch level changes.

Patch and minor version MUST be reset to 0 when major version is incremented. 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 [A-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.

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. Build metadata SHOULD be ignored when determining version precedence. Thus two versions that differ only in the build metadata, have the same precedence. 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.

When major, minor, and patch are equal, a pre-release version has lower precedence than a normal version. 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: 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.

This is not a new or revolutionary idea. In fact, you probably do something close to this already. Without compliance to some sort of formal specification, version numbers are essentially useless for dependency management. By giving a name and clear definition to the above ideas, it becomes easy to communicate your intentions to the users of your software. Once these intentions are clear, flexible but not too flexible dependency specifications can finally be made.

A simple example will demonstrate how Semantic Versioning can make dependency hell a thing of the past. Since Firetruck uses some functionality that was first introduced in 3. Now, when Ladder version 3.

As a responsible developer you will, of course, want to verify that any package upgrades function as advertised.

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What you can do is let Semantic Versioning provide you with a sane way to release and upgrade packages without having to roll new versions of dependent packages, saving you time and hassle. If all of this sounds desirable, all you need to do to start using Semantic Versioning is to declare that you are doing so and then follow the rules. Link to this website from your README so others know the rules and can benefit from them. The simplest thing to do is start your initial development release at 0.

If your software is being used in production, it should probably already be 1. If you have a stable API on which users have come to depend, you should be 1.

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Major version zero is all about rapid development. This is a question of responsible development and foresight. Incompatible changes should not be introduced lightly to software that has a lot of dependent code. The cost that must be incurred to upgrade can be significant. It is your responsibility as a professional developer to properly document software that is intended for use by others.

In the long run, Semantic Versioning, and the insistence on a well defined public API can keep everyone and everything running smoothly. Even under this circumstance, it is unacceptable to modify versioned releases.

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That would be considered compatible since it does not affect the public API. Software that explicitly depends on the same dependencies as your package should have their own dependency specifications and the author will notice any conflicts. Determining whether the change is a patch level or minor level modification depends on whether you updated your dependencies in order to fix a bug or introduce new functionality.

Use your best judgment. If you have a huge audience that will be drastically impacted by changing the behavior back to what the public API intended, then it may be best to perform a major version release, even though the fix could strictly be considered a patch release.

Remember, Semantic Versioning is all about conveying meaning by how the version number changes. If these changes are important to your users, use the version number to inform them. Deprecating existing functionality is a normal part of software development and is often required to make forward progress.

When you deprecate part of your public API, you should do two things: Before you completely remove the functionality in a new major release there should be at least one minor release that contains the deprecation so that users can smoothly transition to the new API. No, but use good judgment. A character version string is probably overkill, for example.

Also, specific systems may impose their own limits on the size of the string. The Semantic Versioning specification is authored by Tom Preston-Werner , inventor of Gravatars and cofounder of GitHub.

MAJOR version when you make incompatible API changes, MINOR version when you add functionality in a backwards-compatible manner, and PATCH version when you make backwards-compatible bug fixes. Why Use Semantic Versioning? FAQ How should I deal with revisions in the 0. How do I know when to release 1. Documenting the entire public API is too much work! What do I do if I accidentally release a backwards incompatible change as a minor version?

What should I do if I update my own dependencies without changing the public API? What if I inadvertently alter the public API in a way that is not compliant with the version number change i. How should I handle deprecating functionality? Does semver have a size limit on the version string?

About The Semantic Versioning specification is authored by Tom Preston-Werner , inventor of Gravatars and cofounder of GitHub. License Creative Commons - CC BY 3.