Medusa Storefront Development

Frontend integration guide for building storefronts with Medusa. Covers SDK usage, React Query patterns, and calling custom API routes.

When to Apply

Load this skill for ANY storefront development task, including:

Calling custom Medusa API routes from the storefront
Integrating Medusa SDK in frontend applications
Using React Query for data fetching
Implementing mutations with optimistic updates
Error handling and cache invalidation

Also load building-with-medusa when: Building the backend API routes that the storefront calls

CRITICAL: Load Reference Files When Needed

The quick reference below is NOT sufficient for implementation. You MUST load the reference file before writing storefront integration code.

Load this reference when implementing storefront features:

Calling API routes? → MUST load
```
references/frontend-integration.md
```
first
Using SDK? → MUST load
```
references/frontend-integration.md
```
first
Implementing React Query? → MUST load
```
references/frontend-integration.md
```
first

Rule Categories by Priority

Priority	Category	Impact	Prefix
1	SDK Usage	CRITICAL	`sdk-`
2	React Query Patterns	HIGH	`query-`
3	Data Display	HIGH (includes CRITICAL price rule)	`display-`
4	Error Handling	MEDIUM	`error-`

Quick Reference

1. SDK Usage (CRITICAL)

```
sdk-always-use
```
- ALWAYS use the Medusa JS SDK for ALL API requests - NEVER use regular fetch()

sdk-existing-methods

- For built-in endpoints, use existing SDK methods (

sdk.store.product.list()

sdk.admin.order.retrieve()

)

```
sdk-client-fetch
```
- For custom API routes, use
```
sdk.client.fetch()
```
```
sdk-required-headers
```
- SDK automatically adds required headers (publishable API key for store, auth for admin) - regular fetch() missing these headers causes errors
```
sdk-no-json-stringify
```
- NEVER use JSON.stringify() on body - SDK handles serialization automatically
```
sdk-plain-objects
```
- Pass plain JavaScript objects to body, not strings
```
sdk-locate-first
```
- Always locate where SDK is instantiated in the project before using it

2. React Query Patterns (HIGH)

```
query-use-query
```
- Use
```
useQuery
```
for GET requests (data fetching)
```
query-use-mutation
```
- Use
```
useMutation
```
for POST/DELETE requests (mutations)
```
query-invalidate
```
- Invalidate queries in
```
onSuccess
```
to refresh data after mutations
```
query-keys-hierarchical
```
- Structure query keys hierarchically for effective cache management

query-loading-states

- Always handle

isLoading

isPending

isError

states

3. Data Display (HIGH)

```
display-price-format
```
- CRITICAL: Prices from Medusa are stored as-is ($49.99 = 49.99, NOT in cents). Display them directly - NEVER divide by 100

4. Error Handling (MEDIUM)

```
error-on-error
```
- Implement
```
onError
```
callback in mutations to handle failures
```
error-display
```
- Show error messages to users when mutations fail
```
error-rollback
```
- Use optimistic updates with rollback on error for better UX

Critical SDK Pattern

ALWAYS pass plain objects to the SDK - NEVER use JSON.stringify():

typescript

// ✅ CORRECT - Plain object
await sdk.client.fetch("/store/reviews", {
  method: "POST",
  body: {
    product_id: "prod_123",
    rating: 5,
  }
})

// ❌ WRONG - JSON.stringify breaks the request
await sdk.client.fetch("/store/reviews", {
  method: "POST",
  body: JSON.stringify({  // ❌ DON'T DO THIS!
    product_id: "prod_123",
    rating: 5,
  })
})

Why this matters:

The SDK handles JSON serialization automatically
Using JSON.stringify() will double-serialize and break the request
The server won't be able to parse the body

Common Mistakes Checklist

Before implementing, verify you're NOT doing these:

SDK Usage:

Using regular fetch() instead of the Medusa JS SDK (causes missing header errors)
Not using existing SDK methods for built-in endpoints (e.g., using sdk.client.fetch("/store/products") instead of sdk.store.product.list())
Using JSON.stringify() on the body parameter
Manually setting Content-Type headers (SDK adds them)
Hardcoding SDK import paths (locate in project first)
Not using sdk.client.fetch() for custom routes

React Query:

Not invalidating queries after mutations
Using flat query keys instead of hierarchical
Not handling loading and error states
Forgetting to disable buttons during mutations (isPending)

Data Display:

CRITICAL: Dividing prices by 100 when displaying (prices are stored as-is: $49.99 = 49.99, NOT in cents)

Error Handling:

Not implementing onError callbacks
Not showing error messages to users
Not handling network failures gracefully

How to Use

For detailed patterns and examples, load reference file:

references/frontend-integration.md - SDK usage, React Query patterns, API integration

The reference file contains:

Step-by-step SDK integration patterns
Complete React Query examples
Correct vs incorrect code examples
Query key best practices
Optimistic update patterns
Error handling strategies

When to Use MedusaDocs MCP Server

Use this skill for (PRIMARY SOURCE):

How to call custom API routes from storefront
SDK usage patterns (sdk.client.fetch)
React Query integration patterns
Common mistakes and anti-patterns

Use MedusaDocs MCP server for (SECONDARY SOURCE):

Built-in SDK methods (sdk.admin., sdk.store.)
Official Medusa SDK API reference
Framework-specific configuration options

Why skills come first:

Skills contain critical patterns like "don't use JSON.stringify" that MCP doesn't emphasize
Skills show correct vs incorrect patterns; MCP shows what's possible
Planning requires understanding patterns, not just API reference

Integration with Backend

⚠️ CRITICAL: ALWAYS use the Medusa JS SDK - NEVER use regular fetch()

When building features that span backend and frontend:

Backend (building-with-medusa skill): Module → Workflow → API Route
Storefront (this skill): SDK → React Query → UI Components
Connection:
- Built-in endpoints: Use existing SDK methods (
```
sdk.store.product.list()
```
  )
- Custom API routes: Use
```
sdk.client.fetch("/store/my-route")
```
- NEVER use regular fetch() - missing publishable API key causes errors

Why the SDK is required:

Store routes need
```
x-publishable-api-key
```
header
Admin routes need
```
Authorization
```
and session headers
SDK handles all required headers automatically
Regular fetch() without headers → authentication/authorization errors

See

building-with-medusa

for backend API route patterns.

building-storefronts

NPX Install

SKILL.md Content