What is API (Application Programming Interface)?
In short
An API (application programming interface) is an agreed way for two pieces of software to exchange data without a human in the middle. Your store calls an API to send an order to a courier, or another system calls your store to update stock levels.
How an API works in practice
One system sends a request, the other answers with structured data. When a customer pays, your store can call the courier's API to create a shipping label, then push the tracking number back to the order. Nobody copies anything by hand.
Access is controlled by keys or tokens, and each integration should only get the permissions it actually needs. Read-only access for a reporting tool, write access for the system that updates stock. Keys belong in the app's settings, never hard-coded in a theme file.
APIs also have rate limits and versions. A connection that works today can break when a provider retires an old version, so integrations need an owner and a habit of checking release notes — not a one-off setup you forget about.
Why it matters for an online store in the EU
Most European stores sell across several channels and run local accounting, invoicing and courier tools. APIs are what keep those systems telling the same story: one stock figure, one order status, one customer record.
A concrete example: a store selling in two countries syncs stock from a single warehouse system through an API. When the last unit sells on a marketplace, the product goes out of stock on the storefront within minutes, so the shop avoids selling something it cannot ship. Under GDPR, also check what personal data each integration receives and where it is stored.
Common mistakes
- Giving every integration full read and write access instead of the minimum it needs.
- Storing API keys in theme files or sharing them over chat.
- Building on an API version without tracking deprecation notices.
- Ignoring rate limits, so bulk updates fail silently during busy periods.
- Having no error handling, so a failed sync is only discovered from customer complaints.
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Try ShopifyFrequently asked questions about APIs
Do I need a developer to use an API?
Not always. Most common connections — accounting, couriers, marketplaces — already exist as apps that handle the API for you. A developer becomes necessary when you need custom logic, an internal system with no ready-made app, or data that must be transformed between the two platforms.
Is an API integration safe?
It is as safe as the permissions and the storage around it. Give each integration the narrowest access that lets it work, keep credentials in the app settings rather than in code, rotate them when someone leaves, and review what personal data each connection receives before enabling it.
What breaks an API integration?
Usually a version change on the provider's side, an expired or revoked key, or hitting rate limits during peak traffic. Assign an owner to every integration, check the provider's release notes, and set up an alert for failed syncs so problems surface before customers notice them.