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Mutation Resolvers

Blitz mutations are plain, asynchronous JavaScript functions that always run on the server.

1. Mutations must be inside a mutations folder. All of the following are valid:

  • src/mutations/createProject.ts
  • src/projects/mutations/createProject.ts
  • src/admin/projects/mutations/createProject.ts

2. Mutations must export a function as the default export

You can write any normal Node.js code here, including database access and fetching from third-party APIs.


  • input: any
    • The first argument is anything you need for your mutation. There are no special requirements.
  • ctx: Ctx
    • This context object is automatically provided by Blitz at run time. This is used by HTTP Middleware to provide data or functions to your mutation. For example, authentication middleware can provide ctx.session with all the data about the current user session.

Example Mutation

// app/products/mutations/createProduct.tsx
import { Ctx } from "blitz"
import db from "db"
import * as z from "zod"

const CreateProject = z
    name: z.string(),

export default async function createProject(
  input: z.infer<typeof CreateProject>,
  ctx: Ctx
) {
  // Validate input - very important for security
  const data = CreateProject.parse(input)

  // Require user to be logged in

  const project = await db.project.create({ data })

  // Can do any processing, fetching from other APIs, etc

  return project

We automatically alias the root of your project, so import db from 'db' is importing <project_root>/db/index.ts

Next, read these docs to see how to use these mutations in your components.

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