Resources · 33
Evolve API contracts without losing clients
Describe requests, responses and errors; test versions and make webhooks safe to replay.
· 20 min
What this guide helps achieve
- Write the contract
- Clarify errors
- Test compatibility
- Plan retirement
Quick check
- Which clients use each operation?
- Do errors have stable types and coherent statuses?
- Can an old client tolerate the change?
- Can retries duplicate an action?
- How will retirement be announced and verified?
Step-by-step method
- 01
Inventory consumers
List operations, clients, usages, versions and owners. Separate observed use from assumptions before changing a field.
Deliverable: contract dependency map.
- 02
Describe requests and responses
Maintain an OpenAPI description with schemas, realistic examples, success and failure responses. Check it against the running service.
Deliverable: versioned contract and conformance tests.
- 03
Stabilize errors
Use HTTP statuses according to their semantics and, where helpful, a documented problem type under RFC 9457. Do not expose secrets in details.
Deliverable: tested error catalog.
- 04
Classify the change
Inspect required fields, types, values, behavior, timeouts and pagination. Test old clients against the new version with representative cases.
Deliverable: compatibility matrix and version decision.
- 05
Make notifications robust
For webhooks, plan authentication, unordered delivery, duplicates and retries. Make processing idempotent where repetition is possible.
Deliverable: replay and acknowledgement scenario.
- 06
Release with an exit path
Publish migration notes, coexistence period and contacts. Measure old-version use and retire only after checking affected consumers.
Deliverable: migration plan and retirement evidence.
Management indicators
| Indicator | What it measures | First action |
|---|---|---|
| Contract | Operations described and matching service behavior | Fix divergence |
| Compatibility | Representative clients tested before change | Add missing cases |
| Errors | Documented types without sensitive data | Revise messages and schemas |
| Migration | Old-version use with an owner | Assist remaining clients |
Common pitfalls
- Assuming a version number alone preserves compatibility
- Documenting only 200 responses
- Returning an internal trace or secret in an error
- Assuming webhooks arrive once and in order
Frequently asked questions
Does OpenAPI replace testing?
No. Compare the description with real responses and consumer needs.
Does every change require a new version?
No. Decide from client impact and contract behavior; incompatible changes need an explicit plan.
Why typed errors?
They give clients a stable way to distinguish problems and choose an action.
Official references
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