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API / Swagger Interview questions

Explain the lifecycle of validating an OpenAPI document with a linter like Spectral?

A linter like Spectral checks an OpenAPI document against a configurable rule set — both structural correctness against the specification itself and style/best-practice rules a team defines — and reports violations before the document is ever published or consumed downstream.

flowchart TD A[OpenAPI document committed/updated] --> B[Spectral loads ruleset - built-in + custom] B --> C[Parse document structure] C --> D[Run each rule against relevant document nodes] D --> E{Violations found?} E -- Yes --> F[Report errors/warnings with severity levels] F --> G[CI pipeline fails build if error-level rules violated] E -- No --> H[Document passes - safe to publish/consume]

Built-in rules catch structural problems — a missing required field, an invalid $ref, a response with no description — while custom rules enforce team-specific conventions, such as requiring every operation to have an operationId, or every error response to follow a standardized problem-details schema.

Wiring this into CI/CD means a spec change that breaks these rules fails the pipeline the same way a failing unit test would, catching documentation quality problems (and, for structural rules, genuinely broken specs) before they reach a published Swagger UI page or get consumed by a code generator further downstream.

What is the purpose of custom rules in an OpenAPI linter?
What happens in CI/CD when an error-level lint rule is violated?

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