Zod Schema Designer

Purpose

Guide the design and implementation of Zod schemas following the project's Zod-first development approach, where schemas are defined before implementing business logic.

When to Use

• Creating new data structures
• Adding validation to inputs
• Designing configuration schemas
• Implementing type-safe transformations
• Creating test data builders

Table of Contents

• Core Principles
• Quick Reference
• Schema Patterns
• Project Schema Location
• References

Core Principles

Zod-First Development

1. Define Schema First: Schema is the source of truth
2. Infer Types: Use z.infer<> instead of manual type definitions
3. Share Validation: Same schema for runtime validation and tests
4. Compose Schemas: Build complex schemas from primitives

Decision Guide

| Need | Pattern | Example | |------|---------|---------| | Basic validation | Primitives | z.string().min(1) | | Domain safety | Branded types | transform((v) => v as EntitySlug) | | Multiple types | Discriminated union | z.discriminatedUnion('type', [...]) | | Cross-field rules | Refinement | .refine((data) => ...) | | Data normalization | Transform | .transform((v) => v.trim()) | | Partial updates | Partial schema | Schema.partial() |

Quick Reference

Common Schema Shapes

import { z } from 'zod';

// String with constraints
const NameSchema = z.string().min(1).max(100).trim();

// Slug pattern
const SlugSchema = z.string().regex(/^[a-z0-9-]+$/);

// Number with range
const PriceSchema = z.number().min(0).multipleOf(0.01);

// Object schema
const EntitySchema = z.object({
  name: z.string().min(1),
  slug: z.string().regex(/^[a-z0-9-]+$/),
  description: z.string().optional(),
});

// Array with validation
const TagsSchema = z.array(z.string()).min(1).max(10);

// Type inference
type Entity = z.infer<typeof EntitySchema>;

Safe Parsing

const result = schema.safeParse(data);

if (!result.success) {
  // Handle errors
  console.error(result.error.issues);
} else {
  // Use validated data
  const validData = result.data;
}

Schema Patterns

For detailed patterns and examples, see:

• Primitive Patterns: Strings, numbers, enums, branded types
• Object Patterns: Objects, discriminated unions, arrays, transforms, refinements
• Testing Patterns: Test data builders, schema validation tests

Project Schema Location

src/modules/config/schema/
├── schema.ts           # Main configuration schema
├── primitives.ts       # Reusable primitive schemas
├── entities/           # Entity-specific schemas
│   ├── category.ts
│   ├── product.ts
│   └── ...
└── index.ts            # Schema exports

Validation Checkpoints

| Phase | Validate | Command | |-------|----------|---------| | Schema defined | No TS errors | npx tsc --noEmit | | Types inferred | z.infer works | Check type in IDE | | Validation works | safeParse tests | pnpm test |

Common Mistakes

| Mistake | Issue | Fix | |---------|-------|-----| | Manual type definitions | Type drift | Use z.infer<typeof Schema> | | Using .parse() directly | Throws on invalid | Use .safeParse() for error handling | | Missing .optional() | Runtime errors | Mark optional fields explicitly | | Complex refinements | Hard to debug | Break into smaller schemas | | Not using branded types | Type confusion | Use .brand() or transform for domain safety |

External Documentation

For up-to-date Zod patterns, use Context7 MCP:

mcp__context7__get-library-docs with context7CompatibleLibraryID: "/colinhacks/zod"

References

• {baseDir}/src/modules/config/schema/schema.ts - Main schema definitions
• {baseDir}/docs/CODE_QUALITY.md#zod-first-development - Quality standards
• Zod documentation: https://zod.dev

Related Skills

• Complete entity workflow: See adding-entity-types for full schema-to-service implementation
• Testing schemas: See analyzing-test-coverage for test data builders
• GraphQL type mapping: See writing-graphql-operations for schema-to-GraphQL patterns

Quick Reference Rule

For a condensed quick reference, see .claude/rules/config-schema.md (automatically loaded when editing src/modules/config/**/*.ts files).