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Fallow is a syntactic analyzer that trades some precision for speed. This page documents the known limitations and how to work around them.
Most limitations only matter in specific project setups. For the majority of JavaScript and TypeScript codebases, fallow produces accurate results out of the box.
Fallow parses source code as syntax trees using Oxc. It does not invoke the TypeScript compiler or resolve type information. This is the core design trade-off that makes fallow fast.Impact: Type-only imports that are elided by the TypeScript compiler (e.g., import type { Foo }) are handled correctly. However, legacy patterns where a value import is used only as a type may cause false positives in rare cases.Workaround: Ensure your project uses isolatedModules: true in tsconfig.json. This is already required by esbuild, swc, and Vite, so most modern projects already have it. With isolatedModules, every import is either explicitly import type or a real value import, eliminating ambiguity.
tsconfig.json
{
  "compilerOptions": {
    "isolatedModules": true
  }
}
In Svelte components, export let declarations serve double duty: they define component props and regular exports. Fallow cannot distinguish between props (which are used by consumers via the template) and utility exports that may genuinely be unused.Impact: Some unused exports in .svelte files may not be reported.Workaround: There is no configuration workaround for this. Review Svelte component exports manually. Utility functions should be extracted into separate .ts files where fallow can track them accurately.
CSS and SCSS files are parsed with lightweight regex extraction rather than a full CSS parser. This covers the most common patterns but not the full CSS specification.What’s tracked:
  • @import and @use statements
  • @forward rules
  • @apply and @tailwind directives (as Tailwind dependency usage)
What’s not tracked:
  • composes: (CSS Modules composition)
  • :global() and :local() pseudo-selectors
  • Complex selector-based dependencies
Workaround: If fallow reports false positives for CSS files that use composes: or :global(), suppress them with ignorePatterns or inline comments.
.fallowrc.json
{
  "ignorePatterns": ["**/legacy-styles/**/*.css"]
}
Fallow tracks class member usage syntactically: it looks for direct references in source code. In NestJS and other DI frameworks, abstract class methods may be invoked at runtime through the DI container without appearing as direct references.Impact: Abstract class methods and properties consumed via dependency injection may be reported as unused.Workaround: Disable unused-class-members for DI-heavy projects:
{
  "rules": {
    "unused-class-members": "off"
  }
}
If your package exports types intended for external consumers (e.g., ButtonProps, Config), fallow will correctly report them as unused within your project, because they are. No internal file imports them.Impact: Correct findings that are noisy for library authors.Workaround: Use ignoreExports to mark public API files:
.fallowrc.json
{
  "ignoreExports": [
    { "pattern": "src/index.ts", "exports": ["*"] },
    { "pattern": "src/types.ts", "exports": ["*"] }
  ]
}
Fallow’s built-in plugins parse config files (e.g., vite.config.ts, jest.config.js) using Oxc’s AST parser. This handles static objects, arrays, and defineConfig() wrappers. However, it cannot evaluate arbitrary JavaScript.What’s handled:
  • Static object literals and arrays
  • defineConfig() / module.exports wrappers
  • String concatenation in simple cases
What’s not handled:
  • Computed property keys
  • Conditional expressions (process.env.NODE_ENV === 'production' ? ... : ...)
  • Nested factory functions
  • Dynamic require() with variables
Workaround: Add undetected entry points manually in your fallow config:
.fallowrc.json
{
  "entry": ["src/dynamic-entry.ts", "scripts/*.ts"]
}
React Native auto-linked native packages (installed via npx pod-install or auto-linking) are not detected as used by fallow. These packages may not have any explicit import in JavaScript code.Impact: Auto-linked packages like react-native-screens or react-native-gesture-handler may be reported as unused dependencies.Workaround: Add auto-linked packages to ignoreDependencies:
.fallowrc.json
{
  "ignoreDependencies": [
    "react-native-screens",
    "react-native-gesture-handler",
    "react-native-safe-area-context"
  ]
}
The fallow LSP server reports column positions as byte offsets rather than character offsets. For ASCII-only source files this makes no difference. For files containing multi-byte characters (emoji, CJK, accented characters), the column number may be off by a few positions.Impact: Diagnostic squiggles in VS Code may be slightly misaligned on lines containing non-ASCII characters.Workaround: This is a cosmetic issue only. The line number and file path are always correct, so navigation still works. A fix is planned for a future release.

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See also

Inline suppression

Suppress individual false positives directly in source code.

Configuration

Full config file reference for ignorePatterns, ignoreExports, and rules.

Agent integration

How agents handle false positives via config and suppression.