Say it like this
- Let's define the API contract upfront to avoid integration issues later.
- We broke the API contract when we changed the response structure.
- The API contract specifies that this endpoint should return a 200 status code on success.
Use it at work
Before building
- Let's agree on the API contract first so both teams can work in parallel.
- I've shared the API contract as an OpenAPI file.
When something breaks
- This change breaks the API contract. Mobile will crash.
- The response doesn't match the API contract. The field is missing.
In a review
- Did you update the API contract for the new field?
- We can't change the API contract without a new version.
Don't say this
API contract is a technical specification, not a legal document. Do not use legal terminology.
Practice
Try it
4 quick exercises
1. Your team wants to change the API response format. What do you say?
2. Before starting development, both teams agreed to _______ the API contract in a shared document.
3. Which sentence uses API contract incorrectly?
4. Rewrite using API contract: The agreement about what the service will send back and what format it will use.
Say it out loud
Phrase 1 of 3
"Let's define the API contract upfront to avoid integration issues later."
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More about API contract
Real examples(3)
- in a standup
"We need to finalize the API contract with the payment service team before Thursday so both teams can proceed in parallel."
- in a code review
"This change violates the API contract because we're removing a required field that clients depend on."
- in a team meeting
"According to the API contract, the authentication endpoint should return a 401 status code for invalid credentials, not a 500 error."
More mistakes(2)
Handle with care. Do not confuse with legal contracts. API contract refers to the technical agreement between services, not a legal document. Also avoid using it to mean error handling or validation alone.
- ✕The API contract handles all error messages.✓The API contract defines how errors should be reported, including error codes and message formats.
An API contract specifies error behavior; it does not actively handle errors. Be precise about what the contract defines.
- ✕We should API contract this endpoint.✓We should document the API contract for this endpoint or establish an API contract.
API contract is a noun. Use verbs like define, establish, or document with it.
Other forms(4)
- API contract noun
"The API contract specifies that the endpoint returns JSON with a user object."
- define the API contract verb phrase
"We should define the API contract before development begins."
- break the API contract verb phrase
"Removing this field will break the API contract for existing clients."
- API contract violation adjective phrase
"The code review flagged an API contract violation in the authentication module."
Often used with(6)
- define the API contract · Establish or create the specification at the start of development.
- establish an API contract · Set up the formal agreement between service provider and consumer.
- break the API contract · Make changes that violate the agreed-upon interface, causing client failures.
- API contract violation · A change or behavior that does not comply with the specification.
- API contract documentation · Written specification of the API contract, often using tools like OpenAPI or Swagger.
- maintain the API contract · Keep the API interface consistent and reliable over time.
Similar words(3)
- API specification · Broader term that includes all technical details; API contract emphasizes the agreement between parties.
- API interface · Refers to the endpoints and methods; API contract includes the expected behavior and responses.
- API agreement · Similar meaning but less common in technical discussions; API contract is the preferred term.
Opposites(2)
- API violation
- breaking changes
Questions(5)
- What does API contract mean in software engineering?
- An API contract is a formal, documented agreement between a service provider and its consumers that specifies the endpoints, request formats, response formats, status codes, and expected behavior of an API. It acts as a contract that both parties rely on to ensure proper integration and communication.
- Why is an API contract important?
- An API contract is important because it allows teams to work independently and in parallel. When both the backend and frontend teams agree on the contract upfront, they can develop without constant synchronization. It also prevents breaking changes that could cause client applications to fail, and it serves as documentation for how the API should be used.
- How do you maintain an API contract?
- To maintain an API contract, ensure that changes are backward compatible, use semantic versioning when breaking changes are necessary, document all changes clearly, and communicate with all teams that depend on the API. Avoid removing fields, changing data types, or altering status codes without proper planning and notification.
- What is the difference between an API contract and an API specification?
- An API contract emphasizes the agreement and promise between provider and consumer, while an API specification is the technical documentation of how the API works. API contract is often used in conversation to highlight the binding nature of the interface, whereas specification is more neutral and technical.
- What tools are used to define API contracts?
- Common tools include OpenAPI (formerly Swagger), GraphQL schema definitions, RAML, and API Blueprint. These tools allow teams to document and version API contracts in a machine-readable format that can be used for validation, testing, and code generation.
