wtf is eslint-tools?

This project is a linter plugin for Firebase Security Rules, the files that control who can read or write data in a Firebase database. It plugs into ESLint, a popular code-checking tool, and automatically catches mistakes in those security rule files before they reach production. Instead of waiting until deployment to discover a syntax error or a rule that accidentally leaves your database wide open, you get immediate feedback right in your editor. Under the hood, it uses the same grammar definition that Firebase itself uses internally to parse and validate rules, which means it catches syntax problems identically to the real deployment pipeline. On top of that, it adds custom checks for semantic issues, things that are technically valid but likely mistakes. Currently it flags three scenarios: rules that allow public read access, rules that allow public write access, and redundant match definitions that overlap in the same scope. The people who benefit most are developers and teams already using Firebase for their backend and ESLint in their JavaScript or TypeScript projects. For example, if you write a rule that says "allow read if true," the plugin warns you that you've just opened read access to the entire internet. That kind of safety net is valuable for any team where a careless one-liner in a security rules file could expose user data. One thing worth noting is the architecture choice: rather than writing a custom parser from scratch, the project leans on ANTLR4, a well-established tool for generating parsers from grammar definitions. This means the plugin stays in sync with how Firebase actually interprets rules. The README also includes a template for contributors who want to add new linting rules, walking the parse tree to find specific patterns and report errors.