Edit Tool Unicode Failure

Edit Tool Unicode Failure Workaround

Problem

The Edit tool's old_string parameter fails to match text containing Unicode characters, even when the string appears identical in Read tool output. This causes silent failures with the error "String to replace not found in file."

Context / Trigger Conditions

• Edit tool returns "String to replace not found in file"
• The old_string visually matches what Read tool shows
• File contains any of these Unicode characters:
  • Emojis: 🚀 👋 🎮 📺 🌏 etc. (multi-byte UTF-8 sequences, 4 bytes each)
  • Em-dashes: — (U+2014, bytes e2 80 94)
  • Non-breaking spaces: (U+00A0, bytes c2 a0) — invisible, looks like regular space
  • Curly/smart quotes: '' "" (U+2018/2019/201C/201D)
  • Other multi-byte Unicode: flags 🇨🇦, variation selectors ✈️

Solution

Option 1: Write the entire file (recommended for files with many Unicode chars)

1. Read the full file with the Read tool
2. Understand the complete content
3. Use the Write tool to rewrite the entire file with your changes
4. This bypasses the string matching entirely

Option 2: Match on ASCII-only substrings

1. Find a unique ASCII-only substring near your target
2. Use Edit with that smaller, ASCII-only old_string
3. Include enough surrounding ASCII context for uniqueness

Option 3: Diagnose with xxd

If unsure whether Unicode is the issue:

sed -n 'Np' /path/to/file | xxd | head -10

Look for multi-byte sequences: f0 9f (emoji), e2 80 94 (em-dash), c2 a0 (NBSP)

Verification

After using Write, re-read the file to confirm changes applied correctly and no content was lost.

Example

Failing approach:

Edit old_string="Moved from Beijing — freely doing what I love 🌏✈️🍁"
→ ERROR: String to replace not found

Working approach:

Read the full file → Write the entire file with modifications

Notes

• The Read tool displays Unicode correctly, but the bytes don't round-trip through Edit's matching
• This issue is especially common in JSX/TSX files with emoji content, markdown files, and i18n strings
• When rewriting with Write, preserve all original content exactly — don't accidentally drop imports, exports, or other sections
• If the file is very large (500+ lines), try Option 2 first to avoid rewriting everything
• Non-breaking spaces (U+00A0) are particularly insidious because they're invisible — use xxd to detect them