trpc/trpc · error · Error

Greeting not found

Error message

Greeting not found

What it means

A documentation example (output-validation.md, v9) using tRPC v9's router().query() API with a custom output validator. It throws 'Greeting not found' when the returned value does not have a string greeting property, showing how to validate resolver output in tRPC v9 before schema libraries were the default.

Source

Thrown at www/versioned_docs/version-9.x/server/output-validation.md:102

});

export type AppRouter = typeof appRouter;
```

### With custom validator

```tsx
import * as trpc from '@trpc/server';
import * as t from 'superstruct';

// [...]

export const appRouter = trpc.router<Context>().query('hello', {
  output: (value: any) => {
    if (value && typeof value.greeting === 'string') {
      return { greeting: value.greeting };
    }
    throw new Error('Greeting not found');
  },
  // expects return type of { greeting: string }
  resolve() {
    return { greeting: 'hello!' };
  },
});

export type AppRouter = typeof appRouter;
```

View on GitHub (pinned to acff82332d)

Solutions

1. Ensure resolve() returns { greeting: string }.
2. Replace the custom validator with a zod/superstruct schema for the output.
3. Update the validator if the resolver contract intentionally changed.

Example fix

// before: resolver returns wrong shape
resolve() { return { message: 'hi' }; }
// after: match the validated shape
resolve() { return { greeting: 'hello!' }; }

// Validate the resolver output before relying on it
function hasGreeting(v: unknown): boolean {
  return typeof v === 'object' && v !== null && typeof (v as any).greeting === 'string';
}

function isGreetingObj(v: unknown): v is { greeting: string } {
  return typeof v === 'object' && v !== null && typeof (v as any).greeting === 'string';
}

When it happens

Trigger: The hello resolver returns a value without a string greeting property (e.g. null, {}, { greeting: 123 }), so the output validator throws.

Common situations: Resolver return shape drifting from the validator; migrating from v9 and forgetting to update the output check; returning undefined from resolve().

Related errors

• Output is not a string
• Invalid input: ${typeof val}
• Input is not a string
• Invalid input: ${typeof val}
• BAD_REQUEST

AI-assisted analysis of trpc/trpc@acff82332d (2026-08-12). Data as JSON: /api/errors/b0c27a7a02ccf3e5. Report an issue: GitHub.