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class-validator

Validates class properties using TypeScript decorators, for browser and Node.js.

GitHub Download v0.15.1
Stars
11.9k
Forks
845
Licence
MIT
Language
TypeScript
Last update
8 months ago
Type
Library

What it is

class-validator lets you attach validation rules to the properties of a class using decorators, such as checking that a string is an email or a number is within a range. You then call validate on an object and get back a list of errors for anything that fails. It also supports non-decorator schemas, and it uses validator.js internally to run the checks.

  • Validate a Post class so that a title length, email address, or numeric rating is checked before saving
  • Return validation errors over HTTP while hiding the target object with validationError: { target: false }
  • Write custom messages with tokens like $value and $property, or with a message function
  • Validate each item of an array, set, or map using the each: true option

Great for

  • TypeScript developers validating request bodies or form data in Node.js or the browser
  • Projects that already model data as classes and want validation rules next to the fields
  • Teams building APIs who want to return structured validation errors to clients

Not ideal for

  • Projects that do not use TypeScript or decorators, since the main API depends on them (the README also offers a non-decorator option, which is less covered in the excerpt)
  • Users who need a full schema language with type inference from one definition, as the README does not compare against such tools
Step-by-step guide: how to use class-validatorInstall, first run, examples, tips and FAQs
class-validator alternativesclass-validator vs Zodclass-validator vs YupAjv vs class-validator

How to get it

  1. 1

    Install with a package manager

    You'll need: Node.js · npm 6 or later

    Install the package

    npm install class-validator --save
  2. 2

    Run it

    • Install the package with npm install class-validator --save.
    • Create a class and add decorators such as @Length, @IsEmail, or @IsInt to its properties.
    • Create an instance, set its values, and call validate(post) to get an array of errors.
    • Check whether the returned array is empty to decide if the object passed.
  3. 3

    Get the most out of it

    • Use validationError: { target: false } when sending errors back over HTTP so the whole object is not exposed.
    • Set custom messages with $constraint1 or $value tokens, or pass a function for more detailed messages.
    • Use each: true on arrays, sets, or maps to validate every item.
    • Use groups in ValidatorOptions to run different rule sets for different situations.

Downloads

Source code (.zip)develop branch · straight from GitHubRelease v0.15.1Release notes and source

Strengths

  • Rules are declared next to the fields they check, which keeps models readable
  • Returns structured ValidationError objects with property names and constraint messages
  • Works in both browser and Node.js environments according to the README

Trade-offs

  • The README says forbidUnknownValues defaults to true and advises keeping it; turning it off lets unknown objects pass validation
  • Requires npm 6 or later so the dependency tree is flattened correctly
  • The README excerpt is truncated, so details of many decorators and advanced features were not reviewed

How it compares

ProjectStarsTypeLevelUpdatedBest for
class-validator (this)11.9kLibrarybeginner8 months agoTypeScript developers validating request bodies or form data in Node.js or the browser
zod44.2kLibrarybeginner6 days agoTypeScript developers who want runtime checks that match their static types
yup23.7kLibrarybeginner6 days agoDevelopers validating form or API input in JavaScript or TypeScript
ajv14.9kLibraryintermediate2 months agoNode.js developers validating API request or response bodies
validator.js23.7kLibrarybeginner2 months agoJavaScript developers validating form or API input on Node.js
vee-validate11.3kLibraryintermediate8 months agoVue developers who need form validation without writing it from scratch

Stats synced from GitHub. The assessment above was drafted with AI from the project's README on 2026-10-29 and may miss recent changes — check the README before relying on a command. MIT licence: free to use, modify and distribute, including commercially, as long as you keep the copyright notice.