Spectral is a generic linter, but you can add an "oas" ruleset, with OAS being shorthand for the OpenAPI Specification.
Add extends: "spectral:oas" to your ruleset file to apply rules for OpenAPI v2 and v3.x, depending on the appropriate OpenAPI version used (detected through formats. See the OpenAPI Rules.
If you would like support for other API description formats like RAML, message formats like JSON:API, etc., we recommend you start building custom but generic rulesets which can be shared with others. We've started putting together some over here on OpenAPI Contrib.