tRPC Tutorial End to End Type Safe APIs with TypeScript

Introduction

Welcome to our tRPC tutorial: End-to-End Type-Safe APIs with TypeScript. In modern web development, building APIs often involves creating separate server and client code, writing schemas, and manually ensuring type safety. This can lead to runtime errors and increased development time.

tRPC solves this by enabling end-to-end type-safe APIs, meaning your client code automatically knows the types from your server without additional code generation or schemas. For Pakistani students learning web development, this means faster development, fewer bugs, and better confidence when building apps.

Whether you are building a Next.js application for a Karachi-based e-commerce store or a social media platform for Lahore students, tRPC allows you to maintain a seamless, type-safe connection between your frontend and backend.

Prerequisites

Before diving into this tutorial, ensure you have the following knowledge:

• TypeScript basics — types, interfaces, and generics.
• Next.js familiarity — pages, API routes, and server-side rendering.
• Node.js and npm — installing packages and running a development server.
• Basic React skills — functional components and hooks (useState, useEffect).

Optional but helpful: Understanding REST and GraphQL APIs to compare how tRPC improves type safety.

Core Concepts & Explanation

tRPC Router: Defining Your API Structure

At the heart of tRPC is the router, which defines the API endpoints and their logic. Unlike traditional REST APIs, you don’t write separate schemas — types are inferred automatically.

// server/routers/user.ts
import { z } from "zod";
import { createRouter } from "../trpc";

export const userRouter = createRouter()
  .query("getUser", {
    input: z.object({ id: z.string() }),
    resolve({ input }) {
      return { id: input.id, name: "Ahmad", city: "Lahore" };
    },
  })
  .mutation("updateUser", {
    input: z.object({ id: z.string(), name: z.string() }),
    resolve({ input }) {
      return { success: true, updatedName: input.name };
    },
  });

Explanation:

• createRouter() – Initializes a new router for your API endpoints.
• .query() – Defines read-only operations.
• .mutation() – Defines write operations that modify data.
• z.object({...}) – Validates input using Zod, ensuring type safety.

Public Procedure & Middleware

tRPC uses procedures to handle requests. Procedures can be public (no authentication) or protected with middleware.

import { publicProcedure } from "../trpc";

export const greetingRouter = createRouter()
  .query("hello", publicProcedure.query(() => "Hello Fatima from Islamabad!"));

Explanation:

• publicProcedure – No authentication required.
• .query() – Returns a simple greeting string.
• Client-side can call this and infer the response type automatically.

Practical Code Examples

Example 1: Fetching a User Profile

Here’s how a Next.js client can fetch a user profile from our tRPC backend:

// pages/index.tsx
import { trpc } from "../utils/trpc";

export default function Home() {
  const { data, isLoading } = trpc.user.getUser.useQuery({ id: "123" });

  if (isLoading) return <div>Loading...</div>;

  return (
    <div>
      <h1>User Profile</h1>
      <p>Name: {data?.name}</p>
      <p>City: {data?.city}</p>
    </div>
  );
}

Line-by-line explanation:

• trpc.user.getUser.useQuery({...}) – Calls the getUser query from the userRouter.
• data – Automatically typed as { id: string; name: string; city: string }.
• isLoading – React Query hook state to show a loading indicator.
• <p>Name: {data?.name}</p> – Safely accesses data without runtime errors.

Example 2: Real-World Application — E-Commerce Cart

Imagine a Karachi-based store updating a shopping cart:

// server/routers/cart.ts
export const cartRouter = createRouter()
  .mutation("addItem", {
    input: z.object({ productId: z.string(), quantity: z.number() }),
    resolve({ input }) {
      console.log(`Added ${input.quantity} of ${input.productId} to cart`);
      return { success: true };
    },
  });

// pages/cart.tsx
const addItem = trpc.cart.addItem.useMutation();

const handleAdd = () => {
  addItem.mutate({ productId: "p101", quantity: 2 });
};

Explanation:

• useMutation() – Sends data to the server to update state.
• mutate() – Executes the mutation with correct types.
• Type safety ensures quantity is always a number, avoiding runtime bugs.

Common Mistakes & How to Avoid Them

Mistake 1: Ignoring Input Validation

Without input validation, server errors can occur:

.query("getUser", {
  resolve({ input }) { return { name: "Ali" }; } // Missing input validation
});

Fix: Always use Zod schemas:

input: z.object({ id: z.string() }),

Mistake 2: Misusing Mutations as Queries

Mutations should change data, queries should fetch data. Using a query to update data breaks caching and React Query assumptions.

Fix: Always distinguish:

• .query() for fetching
• .mutation() for updating

Practice Exercises

Exercise 1: Fetch Lahore Users

Problem: Create a query to fetch all users from Lahore.

Solution:

.query("getLahoreUsers", {
  resolve() {
    return [{ id: "1", name: "Ahmad" }, { id: "2", name: "Fatima" }];
  },
});

Exercise 2: Update User Name

Problem: Create a mutation to update a user’s name in Islamabad.

Solution:

.mutation("updateName", {
  input: z.object({ id: z.string(), name: z.string() }),
  resolve({ input }) {
    return { success: true, updatedName: input.name };
  },
});

Frequently Asked Questions

What is tRPC?

tRPC is a TypeScript-first framework for building end-to-end type-safe APIs without writing schemas or code generation.

How do I integrate tRPC with Next.js?

Install @trpc/server and @trpc/client, define routers, and use hooks like useQuery and useMutation in your Next.js pages.

Is tRPC faster than REST?

Yes, because it avoids extra schema layers and allows direct function calls with type safety.

Can I use tRPC with a database?

Absolutely! tRPC works seamlessly with databases like Prisma, MongoDB, or MySQL.

How does tRPC compare to GraphQL?

tRPC requires no schemas and infers types automatically, while GraphQL needs type definitions and generates TypeScript types separately.

Summary & Key Takeaways

• tRPC enables end-to-end type-safe APIs with TypeScript.
• Routers, queries, and mutations are core concepts.
• Zod validation ensures inputs are safe.
• tRPC integrates naturally with Next.js.
• Avoid common mistakes like skipping validation or confusing queries and mutations.

Next Steps & Related Tutorials

• Learn TypeScript Basics to strengthen type safety knowledge.
• Explore Next.js Tutorial for building modern web apps.
• Dive into Prisma with tRPC for database integration.
• Try React Query with tRPC for advanced data fetching patterns.

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