By default, eslint only lints files with a .js extension[1]. Eslint plugins are what allow eslint to support more languages. A list can be found here[2].

For the record, prettier can also be extended to support more languages[3].

[1] https://eslint.org/docs/latest/use/command-line-interface#--...

[2] https://github.com/dustinspecker/awesome-eslint#plugins

[3] https://prettier.io/docs/en/plugins#official-plugins