A linter is a tool that analyzes source code to flag programming errors, bugs, stylistic errors, and suspicious constructs.
You can use a linter with a pretty printer and a validator. There are, however, usually overlaps between these three types of tools.
There are two approaches to enforcing stylistic conventions:
- a machine algorithmically pretty prints the code (usually based on a maximum line length)
- a human initially formats the code, and a machine fixes-up/warns-about any mistakes
The former is handled by pretty printers, like Prettier, whereas the latter is catered for by the built-in stylistic rules. If you use a pretty printer, you'll want to use stylelint-config-standard and stylelint-config-prettier, which turns off any incompatible rules.
The built-in stylistic rules and plugins are configurable to support a diverse range of stylistic conventions. For example, ordering properties within declaration blocks is a divisive topic, where there isn't a dominant convention. The stylelint-order plugin can be configured to lint and fix a diverse range of ordering conventions.
Another example is the use of single-line rules for sets of related rules, e.g.
/* Single-line related classes */
.class-1 { top: 0; bottom: 0; }
.class-2 { top: 5px; right: 0; }
.class-3 { top: 8px; left: 0; }You can configure the built-in stylistic rules to allow both multi-line and single-line rules. The choice of when to use each belongs to the user.
Validators like CSSTree identify invalid code such as misformed hex colors, unknown language features or invalid property and value pairs.
However, as a stop-gap, Stylelint provides rules for the simplest of cases while these tools mature.