Security & Quality

Joi Data Validation

Validate complex data structures with Joi, the most powerful schema validation library for JavaScript.

Claude Code Cursor Copilot Windsurf

Overview

Joi is the most feature-rich schema validation library for JavaScript, originally developed as part of the hapi.js ecosystem. It provides an extensive API for describing data shapes with over 100 validation rules, including support for strings, numbers, dates, arrays, objects, alternatives, binary data, and custom types.

Joi excels at validating complex, deeply nested data structures with interdependent fields. Its `.when()` method supports complex conditional logic, and `.alternatives()` allows union-type validation with automatic type detection. The library can validate and convert data simultaneously, parsing strings to numbers, ISO strings to dates, and applying custom transformations.

For API validation, Joi integrates with Express through middleware like celebrate, which validates request bodies, query parameters, headers, and cookies against defined schemas. Error messages include the full path to invalid fields, making debugging straightforward. Joi also provides `.describe()` which outputs a JSON description of the schema, useful for generating API documentation automatically.

Who Is This For?

Validate complex API request payloads with nested objects
Define configuration schemas with defaults and coercion
Validate webhook payloads from third-party services
Build reusable validation schemas for database models

Installation

Setup for Claude Code

npm install joi

Configuration

import Joi from "joi"

const schema = Joi.object({
  username: Joi.string().alphanum().min(3).max(30).required(),
  email: Joi.string().email().required(),
  birth_year: Joi.number().integer().min(1900).max(2010),
  role: Joi.string().valid("admin", "user").default("user"),
  metadata: Joi.object().pattern(Joi.string(), Joi.any()),
}).with("username", "email")

const { error, value } = schema.validate(data)