Nestjs Validation Pipes

NestJS Validation & Pipes

Pipes run before route handlers to validate and transform incoming request data. Combined with class-validator and class-transformer, they keep DTOs the single source of truth for input shape and constraints.

When to Apply

• Validating request bodies, query params, or route params in a NestJS app.
• Configuring ValidationPipe (globally or per-route).
• Annotating DTOs with class-validator decorators.
• Coercing param types with built-in parse pipes (ParseIntPipe, ParseUUIDPipe, ...).
• Writing a reusable custom pipe via PipeTransform.

Rules

• global-validation-pipe - Register ValidationPipe once in main.ts so every endpoint is validated.
• whitelist-strip-unknown - Use whitelist + forbidNonWhitelisted to strip or reject unexpected properties.
• transform-payloads - Enable transform: true to auto-instantiate DTO classes and coerce primitive types.
• dto-classes-not-interfaces - Define DTOs as classes; interfaces are erased at runtime and carry no metadata.
• class-validator-decorators - Annotate every DTO field with class-validator decorators.
• nested-object-validation - Use @ValidateNested + @Type to validate nested DTOs and arrays.
• built-in-parse-pipes - Use ParseIntPipe/ParseUUIDPipe/ParseBoolPipe to coerce and validate params.
• custom-pipe-implementation - Implement PipeTransform for reusable custom validation or transformation.

How to Use

Read the relevant file under rules/ for the topic at hand. Each rule states why it matters and shows an incorrect vs. correct example. Apply them when writing or reviewing NestJS input-handling code.