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SemVer validator

Validate semantic versions and parse ranges.

What counts as a version

Strict SemVer 2.0.0 grammar. The three numbers are non-negative ASCII integers without leading zeros.

MAJOR.MINOR.PATCH
breaking / compatible / fixed
1.2.3-alpha.1
prerelease, ranks below 1.2.3
1.2.3+build.5
build metadata, ignored for precedence
1.2.3-0.3
numeric prerelease identifiers are compared as numbers
v1.2.3
not a semantic version (spec FAQ)
01.2.3
not valid: leading zero
1.2.3-01
not valid: zero-padded numeric prerelease
1.2.3+0.09
valid: build metadata may be zero-padded

Range operators

1.2.3
exactly this version
^1.2.3
compatible: >=1.2.3 <2.0.0-0
~1.2.3
patch only: >=1.2.3 <1.3.0-0
>=1.2.3 <2.0.0
AND of comparators in one set
1.2.3 - 2.0.0
inclusive range, spaces required on both sides
1.2.x / 1.x / *
partial versions and wildcards
a || b
union: either set may match
~>1.2.3
npm historical alias, handled as ~1.2.3

How npm fills in partial versions

Verified against node-semver; the -0 suffix is npm sentinel that excludes prereleases of the next series.

RangeExpanded
^1.2.3>=1.2.3 <2.0.0-0
^0.2.3>=0.2.3 <0.3.0-0
^0.0.3>=0.0.3 <0.0.4-0
^1>=1.0.0 <2.0.0-0
~1.2.3>=1.2.3 <1.3.0-0
~1.2>=1.2.0 <1.3.0-0
~1>=1.0.0 <2.0.0-0
1.2.x>=1.2.0 <1.3.0-0
1.x>=1.0.0 <2.0.0-0
1.2.3 - 2.0.0>=1.2.3 <=2.0.0
1.2.3 - 2>=1.2.3 <3.0.0-0
>1.x>=2.0.0

Prerelease precedence

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

Numeric identifiers compare as numbers and rank below alphanumeric ones; a shorter prefix ranks lower. Build metadata never matters.

Common mistakes

These paste straight out of package.json and chat logs.

"1.2.3",
The quotes and comma came along from package.json - paste the version only.
v1.2.3
Git tags carry a v, semantic versions do not.
1.2
Two numbers are a range, not a version.
1.2.3-01
npm loose mode reads it as 1.2.3-1 and silently rewrites it.

Which rule book is used

  • The verdict on a version string is strict SemVer 2.0.0 - no loose mode, no rewriting, no normalising.
  • Ranges follow npm node-semver, because the SemVer spec does not define ranges.
  • This tool is stricter than npm on ranges: a v prefix or a leading zero inside a range is rejected, and an empty side of || is an error rather than "any version".
  • The npm readings shown for an invalid version come from semver.valid(v, {loose:true}) and semver.coerce(v). They are information only - never a pass.
  • Positions count code points and start at 1 in the interface, at 0 in the JSON.

How to use it

  1. Paste a version such as 1.2.3-beta.1+build.5 into the left field. Everything below updates as you type - there is no button to press.
  2. Optionally paste an npm range such as ^1.2.0 on the right to see how the version and the range relate.
  3. Read the badge first: valid or not, and if not, which rule broke at which character.
  4. Tick Include prerelease when you want the npm includePrerelease reading of the range.
  5. Expand JSON result to copy or download the full issue list.

Worked example

Version + range

1.2.3-beta.1+build.5  ^1.2.0

Result

Valid SemVer (MAJOR 1, MINOR 2, PATCH 3, prerelease beta.1, build build.5). ^1.2.0 expands to >=1.2.0 <2.0.0-0, bounds [1.2.0, 2.0.0). Verdict: not satisfied - the set has no prerelease comparator for 1.2.3.

Tick Include prerelease and the same pair becomes satisfied.

Limitations

  • The verdict is strict SemVer 2.0.0, so v1.2.3 and 1.2.3-01 are rejected even though npm loose mode accepts or rewrites them.
  • Ranges follow npm node-semver only - git describe, Cargo, PEP 440 and Go module versions are out of scope.
  • No registry lookups: the tool cannot tell you which version ^1.2.0 would actually install.
  • One version and one range at a time - no batch lists, no sorting, no pairwise comparison, no bump preview.
  • Core numbers above Number.MAX_SAFE_INTEGER are flagged and compared as text, never converted to a JS number.
  • Nothing leaves the page: no network, no storage, no URL parameters - a reload clears everything.

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