Vale

Command-line tool that brings code-like linting to prose. Enforces editorial style guides across Markdown, HTML, and other markup formats while keeping content under your control: runs entirely offline with no server-side processing.

Vale focuses on style consistency across multiple authors rather than grammatical correctness, making it closer to ESLint for prose than to tools like Grammarly. Adoption spans documentation teams at Linode, enterprises, and open-source projects. Vale differentiates through YAML-based custom rules, syntax-aware linting that understands structure, and fine-grained control such as limiting checks to headings or ignoring code blocks by default.

Key capabilities:

• Custom rule framework via YAML with substitution, existence, and conditional checks
• Markup-aware parsing for Markdown, HTML, reStructuredText, and other formats
• CI integration via GitHub Action and command-line output
• Pre-packaged style guides, including Google and Microsoft Documentation
• VS Code extension, browser add-on, and LSP support for editor integration

Documentation teams use Vale to enforce terminology, capitalization, and tone across contributors. Developers integrate it into PR checks to catch style violations before merge. Technical writers rely on Vale for consistent product docs, API references, and knowledge bases.