When a website and mobile application use the same accounts, products, or bookings, a shared API can give both interfaces a consistent way to work with that data. The important planning question is not just which endpoints to build. It is which business rules should stay consistent wherever a customer interacts with your product.
Define the data and permissions before endpoints. Plan validation, useful errors, and maintenance alongside the successful request path.
1. Decide which information is shared
List the business concepts that both interfaces need: profiles, products, bookings, messages, or order statuses. Name the system that owns each piece of information. If an existing payment or inventory service is the source of truth, explain how your product will use it.
Draw a simple flow for a common action. For example, a customer creates a booking on the website and later checks its status in the app. That example exposes the data, permissions, and consistency the API must support.
2. Agree on the request and response contract
For every operation, describe the allowed input, the expected response, and the conditions that can prevent it from succeeding. Name fields clearly and distinguish optional values from required ones. Include pagination or filtering when a list can grow beyond a small set of items.
A contact inquiry might accept a name, email address, selected service, and message. Its response can confirm receipt without returning the complete stored record. A small, predictable response helps the website and app explain what happened to the user.
- The action and its allowed inputs
- The response used by each interface
- Validation errors and missing-record behavior
- List limits, filters, and pagination where needed
3. Make permissions explicit
Signing in establishes who the user is; authorization determines what they can do. Define access for visitors, account holders, support staff, and administrators. A user interface hiding an action does not replace the server checking permission for the request.
Keep private keys and database credentials on the server. Validate requests at the API boundary, use HTTPS for production traffic, and return only the fields the caller should receive. Apply these decisions to individual endpoints, including administration routes.
- Who can read or change each resource
- Server-side checks for protected operations
- Limits on input and response data
- A plan for spam and excessive requests
4. Design for failures and repeated actions
Decide what a user should see when a request is invalid, the connection drops, or a dependency is unavailable. Distinguish a request that can be corrected from a temporary failure that can be retried. Avoid exposing database errors or internal details in public responses.
For actions such as payments or bookings, discuss what happens when the same request reaches the server more than once. The right retry and duplicate-handling approach depends on the operation. Include it in the design before a double tap or interrupted connection produces an unexpected result.
5. Plan documentation and maintenance
Document example requests, response shapes, permissions, and error cases. Test the contract from the website and the app, and decide how changes will be introduced without breaking an already installed mobile release.
Next.js Route Handlers can provide API endpoints within a Next.js application. Whether that is the right home for your backend depends on its integrations, deployment needs, and workload. Start with the product requirements, then agree on the architecture and ongoing ownership with your development team.
- Readable API documentation
- Tests for validation and permissions
- Compatibility with existing app releases
- Operational ownership and monitoring
Further reading
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