# API contract

Concept · [Technical basics](https://ecosystem.samcarlton.com/technical)

Also called: API design, API spec agreement, interface contract

An agreement on exactly what requests an [API](https://ecosystem.samcarlton.com/terms/api) accepts and what responses it returns. Once it is set, [front-end](https://ecosystem.samcarlton.com/front-end) and [back-end](https://ecosystem.samcarlton.com/back-end) work can happen at the same time.

**For example:** The team agrees the API contract for the booking screen on Monday, so the app [developer](https://ecosystem.samcarlton.com/software-engineer) and the [server](https://ecosystem.samcarlton.com/server) developer both start that day.

## Connects to (6)

- [API](https://ecosystem.samcarlton.com/terms/api): Application programming interface.
- [OpenAPI](https://ecosystem.samcarlton.com/openapi): A standard format for describing what an API offers: its addresses, what each one expects and what it returns.
- [Front end](https://ecosystem.samcarlton.com/front-end): The part of an app or website that people see and tap, running in their browser or on their phone.
- [Back end](https://ecosystem.samcarlton.com/back-end): The part of an app that runs out of sight on a server.
- [REST API](https://ecosystem.samcarlton.com/rest-api): A common style of API where each kind of data lives at its own web address and software reads or changes it with standard web requests…
- [Technical requirements document](https://ecosystem.samcarlton.com/technical-requirements-document): A document that explains how a feature will be built: the systems, data and technical choices.

Map view: https://ecosystem.samcarlton.com/api-contract