ast-grep

Overview

Rather than searching source as plain text, ast-grep matches patterns against syntax-tree nodes. That helps target code by its structure, making it useful for finding and changing patterns across many files without relying on one exact formatting or spelling. The CLI can preview and apply rewrites interactively, and the project describes parallel Rust processing for searches and replacements across thousands of source files.

The boundary matters: ast-grep is not a substitute for deeper analysis of program behavior. Its FAQ acknowledges gaps in advanced static-analysis information, so teams that depend on that kind of analysis should pair it with another tool or look elsewhere.

Key features

Search, rewrite, and lint

The scan command runs configurable AST-pattern rules and assigns severities from error through hint. That gives teams a way to encode code-shape checks and surface them consistently, while the interactive rewrite flow makes broad changes easier to inspect before applying. It is a strong fit for repeatable structural refactors; it is less suited to checks that require analysis beyond syntax structure.

Custom rules and testing

Rules are written in YAML and can combine pattern, syntax-kind, regex, relational, and composite conditions. CLI commands help create and test rules, including snapshot-based tests, which makes the rule system more practical to maintain than a collection of one-off search commands. A rule cannot target multiple languages at once: use a superset language with languageGlobs or maintain separate rules for each language.

Languages and integrations

The project supports more than 20 languages and can load custom ones. Its official VS Code extension provides a CLI interface and language-server client; editor guidance also covers Vim, Neovim, and Emacs, with community integrations for other editors. The language server publishes diagnostics and code actions, though lint diagnostics require an sgconfig.yml project file.

APIs and access

A JavaScript API supports programmatic inspection and changes to syntax trees, while a WebAssembly API serves browsers and other WASM environments. The online playground lets users try patterns and rewrite rules without local installation. The CLI is distributed through npm, Cargo, Homebrew, MacPorts, Nix, and pip, and can also be built from source.

Pricing

ast-grep is free and open source, with no paid tier or trial to weigh against its core functionality. The ast-grep plan is 0.00 USD per free. That makes it an easy option to evaluate for an individual or team, though its value depends on whether structural rules meet the need without the advanced analysis it lacks.

Platforms

ast-grep is available across API, extension, Linux, macOS, web, and Windows. Its codebase indexing, regex search, code navigation, IDE extensions, and self-hosted deployment suit developers who want the tool close to their source and editor rather than as a hosted-only service.

Who it's for

Choose ast-grep when you need repeatable, language-aware searches and rewrites, custom lint rules, or a programmable way to inspect syntax trees. Security-focused teams can adapt its example rules, which include checks for a Go JSON tag vulnerability and C/C++ format-string risks. It is a less natural fit when one rule must span multiple languages or when advanced static-analysis data is essential.

Pros and cons

• Pros: Free and open source, with broad language coverage and custom-language support, so teams can apply structural rules across varied codebases without a subscription.
• Pros: Interactive rewrite previews, rule testing, editor integrations, and JavaScript and WebAssembly APIs support workflows from manual refactoring to automation.
• Cons: Rules cannot target multiple languages at once, creating extra maintenance for mixed-language codebases.
• Cons: Some advanced static-analysis information is unsupported, limiting its usefulness as a standalone analysis solution.

Alternatives

For other options, browse Code Refactoring Tools and Code Search Tools.

• CodeRush is an alternative for readers considering a paid product that also offers a free plan and lists the same features and updates across free and paid subscriptions.
• ReSharper is worth considering for readers seeking a freemium alternative with a free non-commercial plan and a free trial.
• Roslynator is another free option, with tools and extensions available free of charge.
• Sourcery may suit readers who want a freemium option with a free open-source plan for public repositories, including AI reviews and one-click fixes.
• Moderne offers a paid route with a fully managed service for readers who prefer a managed offering.
• Scalafix is a free alternative for readers considering another option from the Scala Center.
• Refrax is another free alternative.
• OpenRewrite is a free option for readers looking for a self-hosted alternative.

Verdict

Choose ast-grep if you want a free, flexible way to search, lint, and rewrite code by syntax structure across a broad range of languages. Its combination of custom rules, editor support, APIs, and interactive changes is persuasive for codebase-scale refactoring. Look elsewhere or supplement it when your work depends on advanced static analysis or a single rule spanning several languages.