claude-tab-fix

claude-tab-fix

A Claude Code PreToolUse hook that fixes indentation mismatches in Edit tool calls before they reach the file system.

Problem

Claude Code's Edit tool matches old_string against file content as a literal string. When the model generates old_string with spaces but the file uses tabs (or vice versa), the match fails silently and no edit is applied. This is a persistent issue with Go, .templ, and other tab-indented files.

Installation

prebuilt

go to the right side of this website and look for releases for a bin/exe download. download that

via go

go install github.com/WithHolm/claude-tab-fix@latest

build from source

git clone https://github.com/WithHolm/claude-tab-fix
cd claude-tab-fix
make install

Setup

As a plugin (recommended)

Install the binary first, then install the plugin so Claude Code picks up the hook automatically:

# 1. Install the binary
go install github.com/WithHolm/claude-tab-fix@latest

# 2. Install the plugin
/plugin marketplace add WithHolm/claude-tab-fix
/plugin install claude-tab-fix@WithHolm/claude-tab-fix

The plugin registers the PreToolUse hook for you — no manual config editing needed.

Manually

Install the binary, then add the hook to your Claude Code settings.

Per-project — commit .claude/settings.json to your repo so anyone who clones it gets the hook automatically:

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Edit",
        "hooks": [
          {
            "type": "command",
            "command": "claude-tab-fix"
          }
        ]
      }
    ]
  }
}

Globally — add the same block to ~/.claude/settings.json to enable it for every project on your machine.

If the binary is not on your PATH, use the full path: $(go env GOPATH)/bin/claude-tab-fix.

How it works

Before every Edit tool call, the hook:

1. Reads the target file and detects its dominant indent style (tabs or N-spaces)
2. Detects the indent style used in old_string
3. If they differ, re-indents both old_string and new_string to match the file
4. If the re-indented old_string isn't found verbatim, falls back to fuzzy line-similarity matching to handle minor content drift
5. Exits with code 2 and prints the corrected strings to stderr — Claude Code surfaces this as feedback, causing Claude to retry the Edit with the exact corrected strings

If the indentation already matches, the hook passes through unchanged.

See FLOW.md for the full decision diagram.

Edge cases handled

The hook fires on Edit, Bash, and Write. Only Edit calls can be automatically corrected — Bash and Write bypass the normalization path, so the hook injects a strong suggestion to use Edit instead. A CLAUDE.md file is included in the release archive; placing it in your project root reinforces this at session start.

Development

make build   # build ./claude-tab-fix binary
make fmt     # run gofmt
make install # go install
go test ./...