Input & Output Validators

tRPC procedures may define validation logic for their input and/or output, and validators are also used to infer the types of inputs and outputs. We have first class support for many popular validators, and you can integrate validators which we don't directly support.

Input Validators

By defining an input validator, tRPC can check that a procedure call is correct and return a validation error if not.

To set up an input validator, use the procedure.input() method:

ts
// Our examples use Zod by default, but usage with other libraries is identical
import { z } from 'zod';
 
export const t = initTRPC.create();
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .input(
      z.object({
        name: z.string(),
      }),
    )
    .query((opts) => {
      const name = opts.input.name;
             
const name: string
      return {
        greeting: `Hello ${opts.input.name}`,
      };
    }),
});

ts
// Our examples use Zod by default, but usage with other libraries is identical
import { z } from 'zod';
 
export const t = initTRPC.create();
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .input(
      z.object({
        name: z.string(),
      }),
    )
    .query((opts) => {
      const name = opts.input.name;
             
const name: string
      return {
        greeting: `Hello ${opts.input.name}`,
      };
    }),
});

Input Merging

.input() can be stacked to build more complex types, which is particularly useful when you want to utilise some common input to a collection of procedures in a middleware.

ts
const baseProcedure = t.procedure
  .input(z.object({ townName: z.string() }))
  .use((opts) => {
    const input = opts.input;
           
const input: {
    townName: string;
}
 
    console.log(`Handling request with user from: ${input.townName}`);
 
    return opts.next();
  });
 
export const appRouter = t.router({
  hello: baseProcedure
    .input(
      z.object({
        name: z.string(),
      }),
    )
    .query((opts) => {
      const input = opts.input;
             
const input: {
    townName: string;
    name: string;
}
      return {
        greeting: `Hello ${input.name}, my friend from ${input.townName}`,
      };
    }),
});

ts
const baseProcedure = t.procedure
  .input(z.object({ townName: z.string() }))
  .use((opts) => {
    const input = opts.input;
           
const input: {
    townName: string;
}
 
    console.log(`Handling request with user from: ${input.townName}`);
 
    return opts.next();
  });
 
export const appRouter = t.router({
  hello: baseProcedure
    .input(
      z.object({
        name: z.string(),
      }),
    )
    .query((opts) => {
      const input = opts.input;
             
const input: {
    townName: string;
    name: string;
}
      return {
        greeting: `Hello ${input.name}, my friend from ${input.townName}`,
      };
    }),
});

Output Validators

Validating outputs is not always as important as defining inputs, since tRPC gives you automatic type-safety by inferring the return type of your procedures. Some reasons to define an output validator include:

• Checking that data returned from untrusted sources is correct
• Ensure that you are not returning more data to the client than necessary

info

If output validation fails, the server will respond with an INTERNAL_SERVER_ERROR.

ts
import { z } from 'zod';
 
export const t = initTRPC.create();
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .output(
      z.object({
        greeting: z.string(),
      }),
    )
    .query((opts) => {
      return {
        gre,
           
greeting
      };
    }),
});

ts
import { z } from 'zod';
 
export const t = initTRPC.create();
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .output(
      z.object({
        greeting: z.string(),
      }),
    )
    .query((opts) => {
      return {
        gre,
           
greeting
      };
    }),
});

The most basic validator: a function

You can define a validator without any 3rd party dependencies, with a function.

info

We don't recommend making a custom validator unless you have a specific need, but it's important to understand that there's no magic here - it's just typescript!

In most cases we recommend you use a validation library

ts
import { initTRPC } from '@trpc/server';
 
export const t = initTRPC.create();
 
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .input((value): string => {
      if (typeof value === 'string') {
        return value;
      }
      throw new Error('Input is not a string');
    })
    .output((value): string => {
      if (typeof value === 'string') {
        return value;
      }
      throw new Error('Output is not a string');
    })
    .query((opts) => {
      const { input } = opts;
               
const input: string
      return `hello ${input}`;
    }),
});
 
export type AppRouter = typeof appRouter;

ts
import { initTRPC } from '@trpc/server';
 
export const t = initTRPC.create();
 
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .input((value): string => {
      if (typeof value === 'string') {
        return value;
      }
      throw new Error('Input is not a string');
    })
    .output((value): string => {
      if (typeof value === 'string') {
        return value;
      }
      throw new Error('Output is not a string');
    })
    .query((opts) => {
      const { input } = opts;
               
const input: string
      return `hello ${input}`;
    }),
});
 
export type AppRouter = typeof appRouter;

Library integrations

tRPC works out of the box with a number of popular validation and parsing libraries. The below are some examples of usage with validators which we officially maintain support for.

With Zod

Zod is our default recommendation, it has a strong ecosystem which makes it a great choice to use in multiple parts of your codebase. If you have no opinion of your own and want a powerful library which won't limit future needs, Zod is a great choice.

ts
import { initTRPC } from '@trpc/server';
import { z } from 'zod';
 
export const t = initTRPC.create();
 
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .input(
      z.object({
        name: z.string(),
      }),
    )
    .output(
      z.object({
        greeting: z.string(),
      }),
    )
    .query(({ input }) => {
               
(parameter) input: {
    name: string;
}
      return {
        greeting: `hello ${input.name}`,
      };
    }),
});
 
export type AppRouter = typeof appRouter;

ts
import { initTRPC } from '@trpc/server';
import { z } from 'zod';
 
export const t = initTRPC.create();
 
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .input(
      z.object({
        name: z.string(),
      }),
    )
    .output(
      z.object({
        greeting: z.string(),
      }),
    )
    .query(({ input }) => {
               
(parameter) input: {
    name: string;
}
      return {
        greeting: `hello ${input.name}`,
      };
    }),
});
 
export type AppRouter = typeof appRouter;

With Yup

ts
import { initTRPC } from '@trpc/server';
import * as yup from 'yup';
 
export const t = initTRPC.create();
 
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .input(
      yup.object({
        name: yup.string().required(),
      }),
    )
    .output(
      yup.object({
        greeting: yup.string().required(),
      }),
    )
    .query(({ input }) => {
               
(parameter) input: {
    name: string;
}
      return {
        greeting: `hello ${input.name}`,
      };
    }),
});
 
export type AppRouter = typeof appRouter;

ts
import { initTRPC } from '@trpc/server';
import * as yup from 'yup';
 
export const t = initTRPC.create();
 
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .input(
      yup.object({
        name: yup.string().required(),
      }),
    )
    .output(
      yup.object({
        greeting: yup.string().required(),
      }),
    )
    .query(({ input }) => {
               
(parameter) input: {
    name: string;
}
      return {
        greeting: `hello ${input.name}`,
      };
    }),
});
 
export type AppRouter = typeof appRouter;

With Superstruct

ts
import { initTRPC } from '@trpc/server';
import { object, string } from 'superstruct';
 
export const t = initTRPC.create();
 
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .input(object({ name: string() }))
    .output(object({ greeting: string() }))
    .query(({ input }) => {
               
(parameter) input: {
    name: string;
}
      return {
        greeting: `hello ${input.name}`,
      };
    }),
});
 
export type AppRouter = typeof appRouter;

ts
import { initTRPC } from '@trpc/server';
import { object, string } from 'superstruct';
 
export const t = initTRPC.create();
 
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .input(object({ name: string() }))
    .output(object({ greeting: string() }))
    .query(({ input }) => {
               
(parameter) input: {
    name: string;
}
      return {
        greeting: `hello ${input.name}`,
      };
    }),
});
 
export type AppRouter = typeof appRouter;

With scale-ts

ts
import { initTRPC } from '@trpc/server';
import * as $ from 'scale-codec';
 
export const t = initTRPC.create();
 
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .input($.object($.field('name', $.str)))
    .output($.object($.field('greeting', $.str)))
    .query(({ input }) => {
               
(parameter) input: {
    readonly name: string;
}
      return {
        greeting: `hello ${input.name}`,
      };
    }),
});
 
export type AppRouter = typeof appRouter;

ts
import { initTRPC } from '@trpc/server';
import * as $ from 'scale-codec';
 
export const t = initTRPC.create();
 
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .input($.object($.field('name', $.str)))
    .output($.object($.field('greeting', $.str)))
    .query(({ input }) => {
               
(parameter) input: {
    readonly name: string;
}
      return {
        greeting: `hello ${input.name}`,
      };
    }),
});
 
export type AppRouter = typeof appRouter;

With Typia

ts
import { initTRPC } from '@trpc/server';
import typia from 'typia';
import { v4 } from 'uuid';
import { IBbsArticle } from '../structures/IBbsArticle';
const t = initTRPC.create();
const publicProcedure = t.procedure;
export const appRouter = t.router({
  store: publicProcedure
    .input(typia.createAssert<IBbsArticle.IStore>())
    .output(typia.createAssert<IBbsArticle>())
    .query(({ input }) => {
      return {
        id: v4(),
        writer: input.writer,
        title: input.title,
        body: input.body,
        created_at: new Date().toString(),
      };
    }),
});
export type AppRouter = typeof appRouter;

ts
import { initTRPC } from '@trpc/server';
import typia from 'typia';
import { v4 } from 'uuid';
import { IBbsArticle } from '../structures/IBbsArticle';
const t = initTRPC.create();
const publicProcedure = t.procedure;
export const appRouter = t.router({
  store: publicProcedure
    .input(typia.createAssert<IBbsArticle.IStore>())
    .output(typia.createAssert<IBbsArticle>())
    .query(({ input }) => {
      return {
        id: v4(),
        writer: input.writer,
        title: input.title,
        body: input.body,
        created_at: new Date().toString(),
      };
    }),
});
export type AppRouter = typeof appRouter;

With ArkType

ts
import { initTRPC } from '@trpc/server';
import { type } from 'arktype';
 
export const t = initTRPC.create();
 
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .input(type({ name: 'string' }).assert)
    .output(type({ greeting: 'string' }).assert)
    .query(({ input }) => {
               
(parameter) input: {
    name: string;
}
      return {
        greeting: `hello ${input.name}`,
      };
    }),
});
 
export type AppRouter = typeof appRouter;

ts
import { initTRPC } from '@trpc/server';
import { type } from 'arktype';
 
export const t = initTRPC.create();
 
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .input(type({ name: 'string' }).assert)
    .output(type({ greeting: 'string' }).assert)
    .query(({ input }) => {
               
(parameter) input: {
    name: string;
}
      return {
        greeting: `hello ${input.name}`,
      };
    }),
});
 
export type AppRouter = typeof appRouter;

With runtypes

ts
import { initTRPC } from '@trpc/server';
import * as T from 'runtypes';
 
const t = initTRPC.create();
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .input(T.Record({ name: T.String }))
    .output(T.Record({ greeting: T.String }))
    .query(({ input }) => {
               
(parameter) input: {
    name: string;
}
      return {
        greeting: `hello ${input.name}`,
      };
    }),
});
 
export type AppRouter = typeof appRouter;

ts
import { initTRPC } from '@trpc/server';
import * as T from 'runtypes';
 
const t = initTRPC.create();
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .input(T.Record({ name: T.String }))
    .output(T.Record({ greeting: T.String }))
    .query(({ input }) => {
               
(parameter) input: {
    name: string;
}
      return {
        greeting: `hello ${input.name}`,
      };
    }),
});
 
export type AppRouter = typeof appRouter;

With Valibot

ts
import { wrap } from '@decs/typeschema';
import { initTRPC } from '@trpc/server';
import { object, string } from 'valibot';
 
export const t = initTRPC.create();
 
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .input(wrap(object({ name: string() })))
    .output(wrap(object({ greeting: string() })))
    .query(({ input }) => {
               
(parameter) input: {
    name: string;
}
      return {
        greeting: `hello ${input.name}`,
      };
    }),
});
 
export type AppRouter = typeof appRouter;

ts
import { wrap } from '@decs/typeschema';
import { initTRPC } from '@trpc/server';
import { object, string } from 'valibot';
 
export const t = initTRPC.create();
 
const publicProcedure = t.procedure;
 
export const appRouter = t.router({
  hello: publicProcedure
    .input(wrap(object({ name: string() })))
    .output(wrap(object({ greeting: string() })))
    .query(({ input }) => {
               
(parameter) input: {
    name: string;
}
      return {
        greeting: `hello ${input.name}`,
      };
    }),
});
 
export type AppRouter = typeof appRouter;

Contributing your own Validator Library

If you work on a validator library which supports tRPC usage, please feel free to open a PR for this page with equivalent usage to the other examples here, and a link to your docs.

Integration with tRPC in most cases is as simple as meeting one of several existing type interfaces, but in some cases we may accept a PR to add a new supported interface. Feel free to open an issue for discussion. You can check the existing supported interfaces here:

• Types for Inference
• Functions for parsing/validation