NestJS: Format Validation Errors Like Laravel (Frontend-Friendly)
When transitioning from Laravel to NestJS, one thing that quickly stood out was the structure of validation errors. Laravel's validation system returns a clean object with field names as keys and an array of error messages as values. NestJS? Not so much — at least not by default.
I was using Laravel as a backend-for-frontend (BFF), validating data and returning errors that the frontend could easily display inside <p> tags. Once I switched to NestJS, that flow broke — the error structure was too nested and frontend-unfriendly.
In this post, I'll show you how I customized NestJS to return Laravel-style validation errors. It's clean, readable, and makes life easier on the frontend.
🚧The Problem
NestJS returns validation errors in a verbose, nested format — especially when using the built-in ValidationPipe. It contains class names, children, constraints, and more.
But all I wanted was this:
{
"errors": {
"email": ["The email field is required."],
"password": ["The password must be at least 8 characters."]
}
}Just like Laravel. Simple and predictable.
✅The Solution
I created a custom ValidationException and ValidationFilter, then used the exceptionFactory option inside ValidationPipe to override how errors are constructed.
// main.ts (only the relevant part)
app.useGlobalPipes(
new ValidationPipe({
whitelist: true,
forbidNonWhitelisted: true,
exceptionFactory: (errors: ValidationError[]) => {
return new ValidationException(errors);
},
}),
);🛠️Implementation Details
The implementation involves creating custom exception handling that transforms NestJS validation errors into a Laravel-compatible format. Here's the complete solution:
Step 1: Create ValidationException
// validation.exception.ts
import { HttpException, HttpStatus } from '@nestjs/common';
import { ValidationError } from 'class-validator';
export class ValidationException extends HttpException {
constructor(public validationErrors: ValidationError[]) {
super('Validation failed', HttpStatus.UNPROCESSABLE_ENTITY);
}
}Step 2: Create ValidationFilter
// validation.filter.ts
import { ExceptionFilter, Catch, ArgumentsHost, HttpException } from '@nestjs/common';
import { Response } from 'express';
import { ValidationException } from './validation.exception';
@Catch(ValidationException)
export class ValidationFilter implements ExceptionFilter {
catch(exception: ValidationException, host: ArgumentsHost) {
const ctx = host.switchToHttp();
const response = ctx.getResponse<Response>();
const errors = this.formatErrors(exception.validationErrors);
response.status(422).json({
message: 'Validation failed',
errors,
});
}
private formatErrors(validationErrors: any[]): Record<string, string[]> {
const errors: Record<string, string[]> = {};
validationErrors.forEach((error) => {
const field = error.property;
const messages = Object.values(error.constraints || {});
errors[field] = messages as string[];
});
return errors;
}
}Step 3: Update main.ts
// main.ts
import { NestFactory } from '@nestjs/core';
import { ValidationPipe, ValidationError } from '@nestjs/common';
import { AppModule } from './app.module';
import { ValidationException } from './validation.exception';
import { ValidationFilter } from './validation.filter';
async function bootstrap() {
const app = await NestFactory.create(AppModule);
// Global validation pipe with custom exception factory
app.useGlobalPipes(
new ValidationPipe({
whitelist: true,
forbidNonWhitelisted: true,
exceptionFactory: (errors: ValidationError[]) => {
return new ValidationException(errors);
},
}),
);
// Global exception filter
app.useGlobalFilters(new ValidationFilter());
await app.listen(3000);
}
bootstrap();Step 4: Use in DTOs
// user.dto.ts
import { IsEmail, IsNotEmpty, MinLength } from 'class-validator';
export class CreateUserDto {
@IsEmail({}, { message: 'Please provide a valid email address.' })
@IsNotEmpty({ message: 'The email field is required.' })
email: string;
@MinLength(8, { message: 'The password must be at least 8 characters.' })
@IsNotEmpty({ message: 'The password field is required.' })
password: string;
}Result
Now when validation fails, your API returns Laravel-style errors:
{
"message": "Validation failed",
"errors": {
"email": ["Please provide a valid email address."],
"password": ["The password must be at least 8 characters."]
}
}