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☑️ JavaScript fluent validation library

Introducing v8n

v8n is an acronym for validation. Notice that it has exactly eight letters between v and n in the "validation" word. This is the same pattern we are used to seeing with i18n, a11y, l10n ...

Chainable API

Create validations very easily with its chainable API:

  .test("Hello"); // true

Incredibly fluent

Mix rules and modifiers together to create complex validations with great ease and fluency:

  .test([1, 2, -3]); // false - no negative please!

So fluent that it looks like English:

  .some.not.uppercase() // expects that some character is not uppercase
  .test("Hello"); // true

  .not.some.uppercase() // expects that no character is uppercase
  .test("Hello"); // false

Notice how we made very different validation strategies just by changing the order of the modifiers. It's so intuitive that seems to be impossible, but this is v8n.


Create your own custom validation rules in a very intuitive way:

function foo() {
  return value => value === "bar";

v8n.extend({ foo });

v8n will treat them like built-in ones:

  .test("bar"); // true


Export validations just like you're used to do with your JavaScript modules:


import v8n from "v8n";

export default v8n()
  .between(50, 100)

and use them anywhere you want:

import specialNumber from "../specialNumber";

specialNumber.test(63); // true

For any kind of data

Use v8n to validate your data regardless of its type. You can validate primitives, arrays, objects and whatever you want! You can also use them together!

// numbers
  .between(5, 10)
  .test(7); //true

// strings
  .test("foo"); // true

// arrays
  .test([2, 4, 6]); // true

// objects
const myData = { id: "fe03" };

    id: v8n().string()
  .test(myData); // true

For any kind of validation

Do simple validations with boolean based tests. Get more information about your validation process with exception based tests. And of course, perform asynchronous tests as well. All in one library.

Boolean based validation:

  .test("Hello"); // true

Exception based validation:

try {
} catch (ex) {
  console.log(; // first

Getting all failures:

const failed = v8n()

// [
//   ValidationError { rule: { name: "string", ... } },
//   ValidationError { rule: { name: "minLength", ... } }
// ]

Async validation:

If your validation strategy has some rule that performs time consuming validation, like a back-end check, you should use asynchronous validation:

  .testAsync("foo") // returns a Promise
  .then(result => {
    /* valid! */
  .catch(ex => {
    /* invalid! */


Share your rules with the world, and use theirs as well.

Create useful validation rules and share them with the open source community, and let people around the world validate without reinventing the wheel.

Ready to use!

There are a lot of built-in rules and modifiers for you to use already implemented in v8n's core. Take a look at all of them in our API page. But if you can't find what you need, go ahead and make it.


All these incredible features for just a few bytes:

npm bundle size (minified + gzip)


The v8n core is composed of rules and modifiers. They are used together to build complex validations in an easy way.


Rules are the heart of the v8n ecosystem. You use them to build your validation strategies:

  .test("Hello"); // true

In this code snippet, we're using two rules (string and minLength) to build our validation strategy. So our validated value ("Hello") is valid because it's a string and it is at least 3 characters long.

Rules can be more powerful if used along with modifiers. Learn about them in the next section.


Modifiers can be used to change rules meaning. For example, you can use the not modifier to expect the reversed result from a rule:

  .test(5); // false

You can check all available modifiers on our documentation page.

Modifiers are very powerful. They work as decorators for rules. When used together, they allow you to build very complex validations.


Contributions of any kind are welcome! Read our CONTRIBUTING guide.


MIT License

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