API integration planning: what to clarify first
From data ownership to failure handling: these questions separate a dependable system connection from fragile data transfer.
AT A GLANCE
Before planning an API integration, define the source of truth, transferred fields, permitted actions, access method, and failure handling. Decide what happens after a timeout, repeated request, or partial success, who sees stalled work, and how the transfer is verified. The existence of an API does not by itself make a workflow dependable.
- Assign an authoritative source and owner for each data set.
- A repeated request must not create a duplicate business action.
- Logs should reveal state without copying unnecessary sensitive data.
1. Decide which system is authoritative for each data set
A customer name may be authoritative in the CRM, invoice status in billing, and permissions in an internal system. Do not search for one universal “master system”. For each data set, record where a value originates, which system may change it, and what happens when values conflict. A two-way connection can easily create endless overwrites or restore stale data when ownership is unclear.
Document the trigger and intended business outcome too. A daily list synchronisation needs a different design from creating a task immediately after approval. Frequency, acceptable delay, and the point of human intervention should be visible before implementation begins.
2. Create a field map and a testable contract
For every transferred value, document its source field, destination field, format, requirement, and transformation rule. Treat identifiers, currencies, time zones, statuses, and missing values explicitly. Labels such as “name” or “date” are rarely precise enough; ambiguous mappings often remain hidden until production data appears.
An OpenAPI description can document endpoints, parameters, and responses in a machine-readable form, but it does not replace business rules. The design therefore needs a technical contract and examples people can review: an ordinary case, an incomplete request, and a response the destination rejects.
3. Keep access narrow and revocable
Do not share a common login or a fully privileged key merely because it makes a pilot faster. Define which system initiates the connection, which data it may access, and which actions it may perform. OAuth 2.0 enables limited access to an HTTP service, but the exact authorisation method must be selected from the provider documentation and the operating context.
Secrets should not enter source code, form content, or logs. Give key rotation and revocation an owner, and test what happens when access expires. Development and production should have separate credentials so a test cannot accidentally modify real customer data.
4. Design retries without duplicate work
After a timeout, the caller may not know whether the other system completed the operation. Blindly sending it again can create two orders, invoices, or notifications. Use a unique operation identifier, observable state, and retry rules that distinguish temporary from permanent failures. RFC 9110 defines an idempotent method as having the same intended effect when repeated; automatically repeating a non-idempotent request needs an additional safeguard.
Account for provider limits and backlogs too. A bad record should not silently stop the whole queue, nor should it disappear. Give it a clear reason, an owner, and a safe reprocessing route. After partial success, show exactly which step completed and which action must not be repeated.
5. Include monitoring and recovery in the handover
A “200 OK” response does not prove that the correct business data reached the correct case. Acceptance tests should cover the ordinary path, a missing field, permission failure, timeout, repeated request, and destination rejection. Add a reconciliation count or checkpoint that reveals when an item has gone missing on either side.
After launch, show successful, waiting, and failed operations, the oldest stalled item, and the person responsible for intervention. Logs must not contain complete access tokens or unnecessary personal data. Document how to stop the connection, safely reprocess an item, and respond when the external API changes.
A PRACTICAL TEMPLATE
API integration planning sheet
For one data transfer, record the source of truth, field map, access method, retry safeguards, exception owner, and handover verification.
- Source of truth and destination
- Field map and business rule
- Access and duplicate protection
- Failure owner, logs, and reconciliation
Sources and further reading
- RFC 9110: HTTP SemanticsRFC Editor · Checked: 2026-11-02
- RFC 6749: The OAuth 2.0 Authorization FrameworkRFC Editor · Checked: 2026-11-02
- OpenAPI Specification 3.1OpenAPI Initiative · Checked: 2026-11-02
Kristóf Borbély
The developer behind Kriside, writing practical guides about web systems, automation, and AI solutions.