"Epoch Semantic Versioning" or "Epoch SemVer" contains a set of rules and requirements that dictate how version numbers are assigned and incremented. It differs from Semantic Versioning by introducing an epoch version, which either creates a leading 4th number or a 3rd number with a zero-padded divider between the epoch and breaking versions that is both machine-readable and understandable by humans.

Given a version number of EPOCH.BREAKING.ADDING.PATCH OR {(EPOCH * 100000) + BREAKING}.ADDING.PATCH, increment the:

1. EPOCH version when you make marketably significant or marketably groundbreaking changes, so long as they also have incompatible API changes
2. BREAKING version when you make incompatible API changes
3. ADDING version when you add functionality in a backward compatible manner
4. PATCH version when you make backward compatible bug fixes

Additional labels for pre-release and build metadata are available as extensions to the formats EPOCH.BREAKING.ADDING.PATCH and {(EPOCH * 100000) + BREAKING}.ADDING.PATCH.

For compatibility with existing ecosystems and projects that enforce or use regular Semantic Versioning, use {(EPOCH * 100000) + BREAKING}.ADDING.PATCH. Otherwise, consider using EPOCH.BREAKING.ADDING.PATCH instead.

In the world of software management there exists a dreaded place called "dependency hell." The bigger your system grows and the more packages you integrate into your software, the more likely you are to find yourself, one day, in this pit of despair.

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). Dependency hell is where you are when version lock and/or version promiscuity prevent you from easily and safely moving your project forward.

As a solution to this problem, we 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 A.X.Y.Z (Epoch.Breaking.Adding.Patch). Bug fixes not affecting the API increment the patch version, backward compatible API additions/changes increment the adding version, backward incompatible API changes increment the breaking version, and marketable changes increment the epoch version.

We call this system "Epoch Semantic Versioning." Under this scheme, version numbers and the way they change convey meaning about the underlying code and what has been modified from one version to the next.

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 Epoch 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 either take the form X.Y.Z or A.X.Y.Z, where A, X, Y, and Z are non-negative integers, and MUST NOT contain leading zeroes. When the version number leads with A, then A is the epoch version, X is the breaking version, Y is the adding version, and Z is the patch version. When the version number leads with X; then X is the epoch version multiplied by 100000, plus the breaking version; Y is the adding version; and Z is the patch version. Each element MUST increase numerically. For instance: 4.2.9.0 -> 4.2.10.0 -> 4.2.11.0.

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. Breaking version zero (a.0.y.z) AND epoch version zero (0.x.y.z) are for initial development. Anything MAY change at any time. The public API SHOULD NOT be considered stable.

5. When on epoch version zero (0.x.y.z), the breaking version (0.X.y.z) MUST also remain at zero (0.0.y.z).

6. When on epoch version 1 and breaking version zero and using {(EPOCH * 100000) + BREAKING}.ADDING.PATCH to present your version, said version MUST be presented as 1.y.z instead of 100000.y.z.

7. Epoch version 1 (1.y.z OR 1xxxx.y.z OR 1.x.y.z) 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.

8. Patch version Z (a.x.y.Z OR {a * 100000 + x}.y.Z | x > 0 OR a > 0) MUST be incremented if only backward compatible bug fixes are introduced. A bug fix is defined as an internal change that fixes incorrect behavior.

9. Adding version Y (a.x.Y.z OR {a * 100000 + x}.Y.z | x > 0 OR a > 0) MUST be incremented if new, backward 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 adding version is incremented.

10. Breaking version X (a.X.y.z OR {a * 100000 + X}.y.z | X > 0 OR a > 0) MUST be incremented if any backward incompatible changes are introduced to the public API. It MAY also include adding and patch level changes. Patch and adding versions MUST be reset to 0 when breaking version is incremented.

11. Breaking version X (a.X.y.z OR {a * 100000 + X}.y.z | X > 0 OR a > 0) MUST not exceed 9999.

12. Epoch version A (A.x.y.z OR {A * 100000 + x}.y.z | x > 0 OR A > 0) SHOULD be incremented if any marketably significant or marketably groundbreaking changes are introduced to the public API. This is intentionally vague and subjective to allow flexibility, as what this means for your project may differ. It MUST only be incremented if any backward incompatible changes are introduced to the public API alongside it. It MAY also include breaking, adding, and patch level changes. Breaking, patch, and adding versions MUST be reset to 0 when epoch version is incremented.

13. 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 hyphens [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: 1.0.0.0-alpha, 1.0.0.0-alpha.1, 1.0.0.0-0.3.7, 1.0.0.0-x.7.z.92, 1.0.0.0-x-y-z.--.

14. 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 hyphens [0-9A-Za-z-]. Identifiers MUST NOT be empty. Build metadata MUST be ignored when determining version precedence. Thus two versions that differ only in the build metadata, have the same precedence. Examples: 1.0.0.0-alpha+001, 1.0.0.0+20130313144700, 1.0.0.0-beta+exp.sha.5114f85, 1.0.0.0+21AF26D3----117B344092BD.

15. Precedence refers to how versions are compared to each other when ordered.

    1. Precedence MUST be calculated by separating the version into epoch, breaking, adding, patch and pre-release identifiers in that order (Build metadata does not figure into precedence).

    2. Precedence is determined by the first difference when comparing each of these identifiers from left to right as follows: Epoch, breaking, adding, and patch versions are always compared numerically.

       Example: 1.0.0.0 < 2.0.0.0 < 2.1.0.0 < 2.1.1.0 < 2.1.1.1.

    3. When epoch, breaking, adding, and patch are equal, a pre-release version has lower precedence than a normal version:

       Example: 1.0.0.0-alpha < 1.0.0.0.

    4. Precedence for two pre-release versions with the same epoch, breaking, adding, and patch version MUST be determined by comparing each dot separated identifier from left to right until a difference is found as follows:

       1. Identifiers consisting of only digits are compared numerically.

       2. Identifiers with letters or hyphens are compared lexically in ASCII sort order.

       3. Numeric identifiers always have lower precedence than non-numeric identifiers.

       4. A larger set of pre-release fields has a higher precedence than a smaller set, if all of the preceding identifiers are equal.

       Example: 1.0.0.0-alpha < 1.0.0.0-alpha.1 < 1.0.0.0-alpha.beta < 1.0.0.0-beta < 1.0.0.0-beta.2 < 1.0.0.0-beta.11 < 1.0.0.0-rc.1 < 1.0.0.0.

<epoch-breaking> is not correctly shown here! Contributions appreciated.

<valid semver> ::= <version core>
                 | <version core> "-" <pre-release>
                 | <version core> "+" <build>
                 | <version core> "-" <pre-release> "+" <build>

<version core> ::= <epoch-breaking> "." <adding> "." <patch>
                 | <epoch> "." <breaking> "." <adding> "." <patch>

<epoch-breaking> ::= <numeric identifier>

<epoch> ::= <numeric identifier>

<breaking> ::= <numeric identifier>

<adding> ::= <numeric identifier>

<patch> ::= <numeric identifier>

<pre-release> ::= <dot-separated pre-release identifiers>

<dot-separated pre-release identifiers> ::= <pre-release identifier>
                                          | <pre-release identifier> "." <dot-separated pre-release identifiers>

<build> ::= <dot-separated build identifiers>

<dot-separated build identifiers> ::= <build identifier>
                                    | <build identifier> "." <dot-separated build identifiers>

<pre-release identifier> ::= <alphanumeric identifier>
                           | <numeric identifier>

<build identifier> ::= <alphanumeric identifier>
                     | <digits>

<alphanumeric identifier> ::= <non-digit>
                            | <non-digit> <identifier characters>
                            | <identifier characters> <non-digit>
                            | <identifier characters> <non-digit> <identifier characters>

<numeric identifier> ::= "0"
                       | <positive digit>
                       | <positive digit> <digits>

<identifier characters> ::= <identifier character>
                          | <identifier character> <identifier characters>

<identifier character> ::= <digit>
                         | <non-digit>

<non-digit> ::= <letter>
              | "-"

<digits> ::= <digit>
           | <digit> <digits>

<digit> ::= "0"
          | <positive digit>

<positive digit> ::= "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"

<letter> ::= "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" | "J"
           | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" | "S" | "T"
           | "U" | "V" | "W" | "X" | "Y" | "Z" | "a" | "b" | "c" | "d"
           | "e" | "f" | "g" | "h" | "i" | "j" | "k" | "l" | "m" | "n"
           | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x"
           | "y" | "z"

The world has already discovered the benefits of Semantic Versioning. It's not a new or revolutionary idea. In fact, you probably do something either close or just like 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. Consider a library called "Firetruck." It requires a Semantically Versioned package named "Ladder." At the time that Firetruck is created, Ladder is at version 3.1.0. Since Firetruck uses some functionality that was first introduced in 3.1.0, you can safely specify the Ladder dependency as greater than or equal to 3.1.0 but less than 4.0.0. Now, when Ladder version 3.1.1 and 3.2.0 become available, you can release them to your package management system and know that they will be compatible with existing dependent software.

Even so, Semantic Versioning has its own problems. To an end user who isn't a developer, a major version increase is viewed as a big deal; even sacred. As a result, major versions have become marketing versions, making the problem worse. To combat this, Epoch Semantic Versioning rebrands "major" and "minor" versions to "breaking" and "fixing" versions, and introduces an epoch version that either creates a leading 4th number or a 3rd number with a zero-padded divider between the epoch and breaking versions that is both machine-readable and understandable by humans. The problem of sacred major versions are largely eliminated because the human brain perceives stimuli logarithmically, numbers included. (See the Weber–Fechner law.)

As a responsible developer you will, of course, want to verify that any package upgrades function as advertised. The real world is a messy place; there's nothing we can do about that but be vigilant. What you can do is let Epoch Semantic Versioning provide you with a sane way to release, upgrade, and if necessary, market 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 Epoch Semantic Versioning is to declare that you are doing so and then follow the rules. Include this file in your project so others know the rules and can benefit from them.

The simplest thing to do is start your initial development release at 0.0.1.0 and then increment the adding version for each subsequent release.

If your software is being used in production, it should probably already be 1.0.0.0. If you have a stable API on which users have come to depend, you should be 1.0.0.0. If you're worrying a lot about backward compatibility, you should probably already be 1.0.0.0. (0.1.x.x is not a valid version, and 1.0.0.0 can also be presented as 1.0.0.)

Epoch version zero is all about rapid development. If you're changing the API every day you should either still be in version 0.0.y.z or on a separate development branch working on the next epoch version.

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. Having to bump breaking versions to release incompatible changes means you'll think through the impact of your changes, and evaluate the cost/benefit ratio involved. This is also part of the reason we add the epoch version. Changes considered "groundbreaking" or marketable have more significance, so "version 42.0.0" won't be as bad for your project once you bump your epoch version a few times and end up at "version 200014.0.0".

It is your responsibility as a professional developer to properly document software that is intended for use by others. Managing software complexity is a hugely important part of keeping a project efficient, and that's hard to do if nobody knows how to use your software, or what methods are safe to call. In the long run, Epoch Semantic Versioning, and the insistence on a well defined public API, can keep everyone and everything running smoothly.

As soon as you realize that you've broken the Epoch Semantic Versioning spec, fix the problem and release a new adding version that corrects the problem and restores backward compatibility. Even under this circumstance, it is unacceptable to modify versioned releases. If it's appropriate, document the offending version and inform your users of the problem so that they are aware of the offending version.

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 adding level modification depends on whether you updated your dependencies in order to fix a bug or introduce new functionality. We would usually expect additional code for the latter instance, in which case it's obviously a adding level increment.

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 breaking 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: (1) update your documentation to let users know about the change, (2) issue a new adding release with the deprecation in place. Before you completely remove the functionality in a new breaking or epoch release, there should be at least one adding release that contains the deprecation so that users can smoothly transition to the new API.

No, but it does have a upwards limit of 9999 for breaking versions. Besides that, specific systems may impose their own limits on the size of the string. Use good judgment. A 255 character version string is probably overkill, for example.

No, "v1.2.3.4" is not an epoch semantic version. However, prefixing an epoch semantic version with a "v" is a common way (in English) to indicate it is a version number. Abbreviating "version" as "v" is often seen with version control. Example: git tag v1.2.3.4 -m "Release version 1.2.3.4", in which case "v1.2.3.4" is a tag name and the epoch semantic version is "1.2.3.4".

Not at this time. Contributions appreciated.

The original idea for Epoch Semantic Versioning used in this specification was shared in a blog post authored by Anthony Fu; member of the core teams of Vue, Nuxt, and Vite. A similar proposal was shared by Andrey Mikhaylov, active developer at Perforce, in this GitHub issue.

A proposal for changing the labeling of Semantic Versioning from MAJOR.MINOR.PATCH to BREAKING.ADDING.FIXING was originally shared in this GitHub issue authored by Brian Graham (or Building Better Teams).

The Semantic Versioning specification was originally authored by Tom Preston-Werner, inventor of Gravatar and cofounder of GitHub.

Epoch Semantic Versioning 0.0.3.3 © 2026 by the Epoch Semantic Versioning team is licensed under Creative Commons Attribution 3.0 Unported. It is based off of Semantic Versioning 2.0.0 by the Epoch Versioning team which is licensed under Creative Commons Attribution 3.0 Unported.