IconVault's Semver Calculator is built on a hand-written semver engine (no npm semver package) that runs 100% client-side. It parses versions, bumps major, minor, patch and prerelease numbers, tests version ranges (`^`, `~`, `>=`, `<=`, `>`, `<`, `=`) and compares two versions, so you can answer questions like whether `1.2.3` satisfies `^1.0.0` before you publish.

It is free with no signup, and everything happens in your browser. The honest note: this implements the widely used npm-style semver conventions. If your ecosystem versions differently (some do), treat the results as a guide and check your package manager's own rules.