Collections and Schemas

What Are Content Collections?

Content Collections are Astro’s built-in system for organizing and validating your Markdown, MDX, and data content. Instead of using loose Astro.glob() calls with manual type casting, collections give you:

• Schema validation — Invalid frontmatter is caught at build time
• Type safety — Full TypeScript autocompletion for frontmatter fields
• Structured querying — getCollection() and getEntry() APIs with typed returns
• Content organization — Named directories with clear boundaries

Defining a Collection

Collections are defined in src/content.config.ts using the defineCollection function:

import { defineCollection, z } from 'astro:content';

const blog = defineCollection({
  type: 'content',
  schema: z.object({
    title: z.string(),
    description: z.string(),
    pubDate: z.coerce.date(),
    author: z.string().default('Anonymous'),
    tags: z.array(z.string()).default([]),
    draft: z.boolean().default(false),
  }),
});

export const collections = { blog };

The type field specifies whether the collection contains content files ('content' for Markdown/MDX) or data files ('data' for JSON/YAML).

Schema Field Types

Zod provides a rich set of validators for your frontmatter. Here are the most commonly used types:

Zod Type	Use Case	Example
z.string()	Text fields	Title, description, author
z.number()	Numeric values	Order, priority, rating
z.boolean()	Flags	Draft, featured, published
z.date() or z.coerce.date()	Dates	Publication date, update date
z.array(z.string())	Lists	Tags, categories
z.enum(['a', 'b'])	Fixed options	Post type, status
z.object({...})	Nested data	SEO metadata, author info

Default Values and Optional Fields

Use .default() to provide fallback values and .optional() for fields that aren’t required:

schema: z.object({
  title: z.string(),                        // Required
  subtitle: z.string().optional(),          // Optional (can be undefined)
  author: z.string().default('Anonymous'),  // Defaults if not provided
  tags: z.array(z.string()).default([]),    // Empty array if not provided
})

Multiple Collections

You can define as many collections as your project needs. Each gets its own directory under src/content/ and its own schema:

const blog = defineCollection({ /* ... */ });
const docs = defineCollection({ /* ... */ });
const authors = defineCollection({ type: 'data', /* ... */ });

export const collections = { blog, docs, authors };

This separation keeps your content organized and each collection’s schema focused on its specific needs.