Cursor Rules Validator
Check supported frontmatter, value types and empty instructions in a Cursor .mdc rule. Legacy .cursorrules text gets a migration hint.
Your rule stays in browser memory. No upload, account or AI request. Input limit: 100 KiB.
Result
Paste text and run the tool to see the result.
These checks do not run Cursor, match files in your repository, or detect conflicts between instructions. A successful check does not guarantee runtime behavior.
What the validator checks
Checks include YAML syntax and duplicate keys, frontmatter boundaries, supported field types, empty body and unsupported fields. Glob checks are textual; the tool cannot test patterns against your repository.
description and globs are optional depending on the rule mode. An always-applied rule uses alwaysApply: true; file-specific rules use globs; a description can guide agent selection; a manual rule can omit both description and globs with alwaysApply: false.
--- alwaysApply: true --- - Read the README before making changes.
A quoted boolean such as alwaysApply: "true" is a type error. A 500-line warning is guidance, not a syntax error.
Sources and limits
Reference checked on October 12, 2026: Cursor Rules documentation and AGENTS.md. This is an independent tool with a limited check set.
Migrate legacy instructions