NestJS API 6: Validation and error messages clients can use

In this chapter

Validation and error messages clients can use

More on Into NestJS

• Moving to NestJS: controllers, services and modules (NestJS)
• NestJS API 5: Reading input: path, query, body and headers
• NestJS API Tutorial 7: Storing data: a real database

Keep learning

• Previous: NestJS API 5: Reading input: path, query, body and headers
• Next: NestJS API Tutorial 7: Storing data: a real database
• All NestJS tutorial chapters

Overview

Design behind this step The design behind this step

The idea

The request has invalid fields. See errors. Your request has invalid fields Send X-User-Id (a stand-in for login until Topic 10) Content-Type: application/json X-User-Id: priya X-User-Id: john

More courses

• Jobs, linked to lessons — Browse jobs where every requirement links to the chapter that teaches it. See how ready you are, how long the gap takes to close, and which listings look stale.
• Match a job post to courses — Paste a job post. Each skill is matched to a track here and put in learning order, foundations first.
• React from open source with patterns — Patterns extracted from Material UI, Radix, React Aria, React Hook Form, Redux Toolkit, TanStack, and Next.js — not slides about hooks.
• Database in depth — How a query becomes work. Indexes, isolation, locks, and the plans that explain why a page is slow — not an ORM tour.
• System Design — Core concepts first (SQL vs NoSQL, CAP, indexing, replication, sharding), then designs grouped by what carries them: the database, Redis, Kafka, or many services.
• Microservices — Microservice patterns one diagram at a time: how to split a monolith, how services talk, and how data stays consistent without distributed transactions.
• Kafka — A beginner-to-senior path through event logs, reliable delivery, production operations, and disaster recovery.
• AI engineering for software engineers — Eight free reads, in order, for software engineers moving into AI: when to build an agent, how to build one, how to test it, and how the model works underneath.
• Frontend system design — How a UI is sliced when it is a product, not a page: ownership of state, cache, routes, and what happens when the network lies.
• TypeScript in depth — The type system as a design tool. Inference, narrowing, generics, and the errors that mean the model is wrong — not a catalog of utility types.
• CSS in depth — See the box, then the page. Visual chapters from the box model through Flexbox surprises, Grid, selectors, and units, then backgrounds, shapes, and visual effects, each with a playground.
• Accessibility — Foundations first (WCAG in plain words, semantic HTML, lists, alt text), then hands-on HTML labs, a full pass of WAI-ARIA 1.3, and a final fix-the-page challenge.
• Docker — What an image is, why layers cache, and how containers find each other on a network.
• Redis — Fifteen Redis patterns, one picture each: cache, session, lock, counter, rate limiter, queue, and when Redis is the wrong tool.
• Kubernetes — Kubernetes from zero to operators: why it exists, Pods, Deployments and Services, then configuration, networking, storage, scheduling, scaling and security.