Commerce Layer API + MCP vs Spree Commerce

Commerce Layer API + MCP

Public OpenAPI 3.0 file and llms.txt. No price between the free plan and a sales-quoted Enterprise contract.

Spree Commerce

A self-hosted BSD 3-Clause platform with public OpenAPI files for the Store and Admin APIs, scoped secret keys, documented rate limits and idempotency keys on cart and checkout calls. GitHub lists six security advisories between January and July 2026, four rated High, and the default docs describe the 6.0 release candidate while 5.6.1 is the stable release.

Commerce Layer API + MCP

1. Call get_resource_schema before any write. Preflight rejects bad filter shapes before they reach the API
2. Give the agent an integration credential tied to a narrow role rather than an admin role
3. On a 429, wait out the sliding window. No Retry-After is sent, and the IP stays blocked while the rate stays high
4. Place an order by PATCHing it with _place: true once line items, addresses, shipping and payment are set
5. Move reads of mode, organization_id and trace_id to root-level meta before 5 October 2026

Spree Commerce

1. Send a publishable key in X-Spree-Api-Key on every Store API call. Add X-Spree-Token with the cart token for guest carts, or a customer JWT as a Bearer token
2. Send Idempotency-Key with the cart token or a customer JWT on cart, payment and completion calls. A request carrying only the publishable key is never cached
3. Ask for fields and expand explicitly. Relations are left out by default and limit stops at 100
4. Use a secret key with the narrowest scopes for the Admin API. read_all gives a read-only key, and the CLI's auto-minted local key is read-only
5. Read the docs under /docs/v5 for a 5.6 store. The default docs describe 6.0, which renames shipments to fulfilments and splits carts from orders