Fix Missing Schema Definitions

Overview

This skill helps diagnose and fix issues caused by steps that lack explicit inputSchema or outputSchema definitions. Schemas are essential for type safety, validation, and proper data serialization between steps.

When to Use This Skill

You're seeing:

• Type errors at step boundaries
• Undefined properties in step inputs/outputs
• Validation failures when passing data between steps
• TypeScript errors about incompatible types
• Runtime errors about unexpected data shapes

Root Cause

Steps without explicit schemas:

• Don't validate input data at runtime
• Don't provide TypeScript type inference
• May serialize/deserialize data incorrectly
• Can pass undefined or malformed data silently

Symptoms

Missing Input Schema

// WRONG: No input validation
export const processData = step({
  name: 'processData',
  // inputSchema: missing!
  outputSchema: z.object({ result: z.string() }),
  fn: async (input) => {
    return { result: input.value };  // input.value might be undefined!
  }
});

Missing Output Schema

// WRONG: No output validation
export const fetchData = step({
  name: 'fetchData',
  inputSchema: z.object({ id: z.string() }),
  // outputSchema: missing!
  fn: async (input) => {
    return { data: await getFromApi(input.id) };  // Output shape not validated
  }
});

Both Schemas Missing

// WRONG: No validation at all
export const transformData = step({
  name: 'transformData',
  // No schemas!
  fn: async (input) => {
    return transform(input);
  }
});

Solution

Always define both inputSchema and outputSchema for every step:

Complete Step Definition

import { z, step } from '@output.ai/core';

export const processData = step({
  name: 'processData',
  inputSchema: z.object({
    id: z.string(),
    value: z.number(),
    optional: z.string().optional(),
  }),
  outputSchema: z.object({
    result: z.string(),
    processedAt: z.number(),
  }),
  fn: async (input) => {
    // input is fully typed: { id: string, value: number, optional?: string }
    return {
      result: `Processed ${input.id}`,
      processedAt: Date.now(),
    };
    // output is validated against outputSchema
  },
});

Schema Definition Best Practices

Use Descriptive Schemas

// Good: Clear, descriptive schema
inputSchema: z.object({
  userId: z.string().uuid(),
  email: z.string().email(),
  age: z.number().int().positive(),
})

Handle Optional Fields

inputSchema: z.object({
  required: z.string(),
  optional: z.string().optional(),
  withDefault: z.string().default('fallback'),
})

Use Schema Composition

// Define reusable schemas
const userSchema = z.object({
  id: z.string(),
  name: z.string(),
});

const addressSchema = z.object({
  street: z.string(),
  city: z.string(),
});

// Compose in step
inputSchema: z.object({
  user: userSchema,
  address: addressSchema,
})

Handle Arrays and Nested Objects

inputSchema: z.object({
  items: z.array(z.object({
    id: z.string(),
    quantity: z.number(),
  })),
  metadata: z.record(z.string()),
})

Finding Steps Without Schemas

Search your codebase:

# Find step definitions
grep -rn "step({" src/workflows/

# Look for steps without inputSchema
grep -A5 "step({" src/workflows/ | grep -B2 "fn:"

# Check if schemas are present
grep -rn "inputSchema:" src/workflows/
grep -rn "outputSchema:" src/workflows/

Review each step definition to ensure both schemas are present.

Benefits of Explicit Schemas

1. Runtime Validation: Catches data errors early
2. Type Safety: Full TypeScript inference in step functions
3. Documentation: Schemas document expected data shapes
4. Serialization: Ensures proper data serialization between steps
5. Error Messages: Clear validation errors when data is wrong

Common Schema Patterns

API Response Steps

export const fetchUser = step({
  name: 'fetchUser',
  inputSchema: z.object({
    userId: z.string(),
  }),
  outputSchema: z.object({
    user: z.object({
      id: z.string(),
      name: z.string(),
      email: z.string(),
    }).nullable(),  // Handle not found
    found: z.boolean(),
  }),
  fn: async (input) => {
    const user = await api.getUser(input.userId);
    return { user, found: user !== null };
  },
});

Transformation Steps

export const transformData = step({
  name: 'transformData',
  inputSchema: z.object({
    raw: z.array(z.unknown()),
  }),
  outputSchema: z.object({
    processed: z.array(z.object({
      id: z.string(),
      value: z.number(),
    })),
    count: z.number(),
  }),
  fn: async (input) => {
    const processed = input.raw.map(transformItem);
    return { processed, count: processed.length };
  },
});

Void Output Steps

For steps that don't return meaningful data:

export const logEvent = step({
  name: 'logEvent',
  inputSchema: z.object({
    event: z.string(),
    data: z.record(z.unknown()),
  }),
  outputSchema: z.object({
    logged: z.literal(true),
  }),
  fn: async (input) => {
    await logger.log(input.event, input.data);
    return { logged: true };
  },
});

Verification

After adding schemas:

1. TypeScript check: npm run output:workflow:build should pass without type errors
2. Runtime test: npx output workflow run <name> '<input>' should validate correctly
3. Invalid input test: Pass invalid data and verify validation errors appear

Related Issues

• For Zod import issues, see output-error-zod-import
• For type mismatches despite schemas, verify schema matches actual data