ESLint is an open-source static analysis tool that finds problematic patterns in JavaScript and TypeScript code. It parses source into an abstract syntax tree, evaluates a configurable set of rules, and reports style violations, likely bugs, and deprecated constructs before they reach production, with many findings fixable automatically.
The official site provides an installation guide, a complete rule reference with correct and incorrect examples, documentation for the flat configuration format, plugin and shareable config authoring, formatter and editor integrations, and migration notes for teams moving from legacy eslintrc files.
It suits front-end and Node.js teams that need a shared coding standard, maintainers of large codebases cleaning up legacy patterns, and continuous integration pipelines that must fail early on unsafe constructs rather than catching them during manual review.
Compared with formatters it focuses on correctness and conventions rather than whitespace; compared with type checkers it is faster and more flexible but cannot prove type safety, so the two categories of tools are usually used together.
Pin the ESLint major version across the team, keep custom rules in a shared config package, enable autofix only in controlled commits, and review new rule proposals carefully since overly strict presets can slow down everyday development work.