---
action: context
tool: (edit|write)
event: after
name: avoid-sync-fs
description: Avoid synchronous filesystem operations
glob: '**/*.{ts,tsx}'
detector: ast
pattern:
    - 'readFileSync($$$)'
    - '$A.readFileSync($$$)'
    - 'writeFileSync($$$)'
    - '$A.writeFileSync($$$)'
    - 'mkdirSync($$$)'
    - '$A.mkdirSync($$$)'
    - 'readdirSync($$$)'
    - '$A.readdirSync($$$)'
    - 'statSync($$$)'
    - '$A.statSync($$$)'
    - 'existsSync($$$)'
    - '$A.existsSync($$$)'
    - 'copyFileSync($$$)'
    - '$A.copyFileSync($$$)'
    - 'unlinkSync($$$)'
    - '$A.unlinkSync($$$)'
    - 'rmdirSync($$$)'
    - '$A.rmdirSync($$$)'
    - 'renameSync($$$)'
    - '$A.renameSync($$$)'
    - 'appendFileSync($$$)'
    - '$A.appendFileSync($$$)'
level: high
suggestSkills:
    - effect-filesystem
---

# Avoid Synchronous Filesystem Operations

```haskell
-- Transformation
readFileSync  :: FilePath → IO String     -- blocks event loop
writeFileSync :: FilePath → String → IO () -- same problem

-- Instead
readFileString  :: FilePath → Effect String FileSystem
writeFileString :: FilePath → String → Effect () FileSystem
```

```haskell
-- Pattern
bad :: FilePath → IO String
bad path = fs.readFileSync path "utf-8"   -- blocking, defeats async

good :: FilePath → Effect String FileSystem
good path = do
  fs ← FileSystem.FileSystem
  fs.readFileString path                  -- non-blocking, composable

-- Sync → Async mapping
readFileSync   → readFileString
writeFileSync  → writeFileString
mkdirSync      → makeDirectory
existsSync     → exists
unlinkSync     → remove
readdirSync    → readDirectory
```

Sync operations block the event loop. Use Effect's FileSystem service for async, composable file operations.