Spring ’26 for Shopify developers: UCP, Catalog API and Sidekick App Extensions
The developer side of Spring ’26 is about agents: open Catalog access, a public checkout MCP endpoint and Sidekick extensions any app can build.
Key takeaways
- Catalog API access now takes just an API key, with no approval, and adds image search, multi-modal search and a lookup endpoint.
- Agents can go from search to checkout by registering an agent profile in the Developer Dashboard and calling a public MCP endpoint.
- Any developer can now build Sidekick App Extensions, with data and action extensions launched alongside 15+ partners.
- Mixed-fulfillment orders reached general availability, so apps that touch checkout logic should be tested against them.
Catalog API: open by default
Shopify’s developer announcement says Catalog access “takes just an API key, no approval needed.” New capabilities include image search, multi-modal search and a lookup endpoint, which makes it practical to build shopping experiences that search across Shopify merchants.
UCP and checkout for agents
Shopify describes UCP as the open standard for how AI agents transact with merchants. To build end-to-end flows from search to checkout, developers register an agent profile in the Developer Dashboard and call the public MCP endpoint, which exposes tools to create, update and complete checkout sessions.
Sidekick App Extensions for every app
Any developer in Shopify’s ecosystem can now build a Sidekick App Extension. Data extensions let Sidekick read from your app, and action extensions let it do things in your app on the merchant’s behalf. For app makers this is a new surface: merchants increasingly ask Sidekick first.
Developer Dashboard
Shopify positions the Developer Dashboard as the home for all building, with dev stores, client transfer stores, collaborator access and overhauled logs and monitoring.
Checklist for Shopify app teams
- Test discount, delivery and payment functions against mixed-fulfillment carts, where shipping and pickup are chosen per item.
- Confirm your checkout logic behaves the same for agent-created checkouts as for storefront checkouts.
- Decide which of your app’s data and actions merchants would want from Sidekick, and scope an extension.
- Move dev stores, logs and collaborators into the Developer Dashboard workflow.
FAQ
How do I get access to Shopify’s Catalog API?
According to Shopify’s Spring ’26 developer announcement, Catalog access takes just an API key, with no approval needed.
Can any developer build a Sidekick App Extension?
Yes. As of the Spring ’26 Edition, any developer in Shopify’s ecosystem can build Sidekick App Extensions, both data and action extensions.
What should app developers test after Spring ’26?
Apps that touch checkout logic should be tested against mixed-fulfillment orders, which reached general availability, and against agent-created checkouts.