SemVer

Semantic Versioning, or SemVer, is a specification for versioning software that expresses meaning about code changes in a version number. The core form is MAJOR.MINOR.PATCH, optionally followed by a pre-release label and build metadata. Examples include 2.4.1, 3.0.0-alpha.2, and 1.2.0+build.40.

Under SemVer, increments signal compatibility: MAJOR increases for incompatible API changes, MINOR for backwards-compatible new features, and PATCH for backwards-compatible bug fixes. Pre-release versions (for example, 1.0.0-beta.1) indicate releases that are not yet stable and may not satisfy dependency constraints. Build metadata (after a plus sign) does not affect version precedence and is used for informational identifiers like build numbers.

The scheme also defines stability and development guidance: 0.y.z is considered initial development and may change at any time; once 1.0.0 is released, public API compatibility is expected to be preserved across subsequent 1.x.y releases unless a new major version is issued. Version constraints in tooling allow specifying compatible ranges, such as ^1.2.3 or >=1.2.0 <2.0.0.

SemVer aims to enable automated dependency management and clearer signaling of compatibility. It is widely adopted in package ecosystems and build tools (such as npm, Cargo, RubyGems, and Composer), though adoption varies and some projects do not strictly follow the spec. The SemVer 2.0.0 specification was published by Tom Preston-Werner in 2013 and formalizes these rules.

Limitations include that version numbers cannot fully guarantee API stability, and some projects may violate the spec or misrepresent compatibility. Nevertheless, SemVer provides a common framework for signaling changes and guiding automated upgrades.