# Contract-First Design

> A design rule that a boundary's contract is written and agreed before the implementation behind it.

Record: `architecture:contract-first-design`
Kind: principle
Layer: [Contracts Core](https://banes-lab.com/records/layer/contracts-core.md)
Severity: recommended
Scope: API, service, integration
Canonical: https://banes-lab.com/ontology#architecture-contract-first-design

Listed in [Architecture principles](https://banes-lab.com/api/records/architecture.md), after [Interface-Based Design](https://banes-lab.com/records/architecture/interface-based-design.md) and before [API Contract](https://banes-lab.com/records/architecture/api-contract.md).

## Repair

- Refactored by: Define Contract, Generate Stubs, Add Contract Tests
- Detected by: absent contract before implementation
- Violated by: generated contracts from unstable implementation
- Measured by: contract-first coverage
- Enforced by: CI contract gates

## Requires

- [Explicit Contracts](https://banes-lab.com/records/architecture/explicit-contracts.md)
- [Schema Contract](https://banes-lab.com/records/architecture/schema-contract.md)

## Reinforces

- [Interoperability](https://banes-lab.com/records/architecture/interoperability.md)
- [Backward Compatibility](https://banes-lab.com/records/architecture/backward-compatibility.md)

## Enables

- [Consumer-Driven Development](https://banes-lab.com/records/lexicon/consumer-driven-development.md)

## Conflicts with

- [Implementation-First Integration](https://banes-lab.com/records/lexicon/implementation-first-integration.md)

## In tension with

- [Iteration Speed](https://banes-lab.com/records/lexicon/iteration-speed.md)

## Tensions

- [Contract-First Design / Iteration Speed](https://banes-lab.com/records/tension/contract-first-design-iteration-speed.md)

## Severity

- [recommended](https://banes-lab.com/records/vocabulary/severity-recommended.md)

## Category

- [Contracts / Interfaces / Compatibility](https://banes-lab.com/records/architecture-category/contracts-interfaces-compatibility.md)

## Reinforced by

- [Consumer-Driven Contracts](https://banes-lab.com/records/architecture/consumer-driven-contracts.md)

## Linked from

- [Contracts / Interfaces / Compatibility](https://banes-lab.com/ontology/principles/architecture-category-contracts-interfaces-compatibility.md)
- [Contracts / Interfaces / Compatibility](https://banes-lab.com/ontology/lexicon/lexicon-category-contracts-interfaces-compatibility.md)
- [Core Vocabulary](https://banes-lab.com/ontology/lexicon/lexicon-category-core-vocabulary.md)
- [Severity levels](https://banes-lab.com/ontology/schema/the-vocabulary-severity.md)
- [The resolutions](https://banes-lab.com/ontology/schema/the-resolutions.md)