API Contract

Kind: constraint

Layer: Contracts Core

Record: architecture:api-contract

Severity: mandatory

Scope: API, service boundary

Canonical: Ontology

A rule or precondition that each endpoint declares its request, response and error shapes in a versioned schema.

Listed in Architecture principles, after Contract-First Design and before Service Contract.

Requires

• Schema
• Versioning
• Stable Interfaces

Reinforces

• Interoperability
• Predictability

Enables

• Client Compatibility

Conflicts with

• Breaking API Change

In tension with

• Evolution

Tensions

• API Contract / Evolution

Violated by

• Ad-Hoc Endpoints
• Inconsistent Error Model

Refactored by

• Define Contract
• Standard Error Contract
• Versioning

Severity

• mandatory

Category

• Contracts / Interfaces / Compatibility

Required by

• Service Contract
• Self-Describing API

Linked from

• Contracts / Interfaces / Compatibility
• Correctness / Determinism / Verification
• Metadata / Self-Description / Declarative Systems
• Contracts / Interfaces / Compatibility
• Core Vocabulary
• Severity levels
• The resolutions