claude-tab-fix

A Claude Code hook that warns Claude about tab-indented files — preventing silent Edit failures and mixed-indentation corruption.

Problem

Claude Code's Read tool formats output as N\t<line content>, using a tab as the line-number separator. For tab-indented files this is visually identical to the file's own indentation — Claude cannot distinguish the separator tab from content tabs, so it often produces old_string with wrong indentation.

Claude Code also validates old_string against the file before calling PreToolUse hooks. This means hooks cannot fix indentation mismatches automatically — they can only warn Claude so it corrects itself.

Installation

prebuilt

go to the right side of this website and look for releases for a bin/exe download. download that. Save the exe in a place where it is safe from deletion, and set PATH to point to this folder.

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 both hooks for you — no manual config editing needed.

Manually

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

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

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Bash",
        "hooks": [{ "type": "command", "command": "claude-tab-fix" }]
      },
      {
        "matcher": "Write",
        "hooks": [{ "type": "command", "command": "claude-tab-fix" }]
      }
    ],
    "PostToolUse": [
      {
        "matcher": "Read",
        "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.

Nice Tip

Add explicit deny for the different commands claude normally uses for edit in the claude settings. the file for your current porject should be in <project root>/.claude/settings.json (or settings.local.json) or in your home/.claude...

for linux the folling commands are recomended (just remove the python3 if you do any python work..)

  "deny": [
    "Bash(sed:*)",
    "Bash(awk:*)",
    "Bash(tr:*)",
    "Bash(xargs:*)",
    "Bash(python3:*)"
  ],

missing info from windows.. if anyone have any info here, please open a pr or write a issue and il add it..

when combined with the added context this tool gives ("hey claude, please remember that the read tool is kinda borked...") it forces claude to fall back into the edit path instead of using any other edit tools:

How it works

PostToolUse / Read — after every Read call on a tab-indented file, the hook injects a context note reminding Claude that the N\t line-number prefix is a separator tab, not part of the file content. Claude uses this information to construct correct old_string with proper tab indentation.

PreToolUse / Bash — before sed, awk, perl, or python commands that target a tab-indented file, the hook warns Claude to use the Edit tool instead, since shell commands bypass indentation awareness.

PreToolUse / Write — before overwriting a tab-indented file, the hook checks whether the new content uses a different indent style. If writing spaces to a tab file (or vice versa), it warns that the result will have mixed indentation and strongly suggests using Edit instead.

Edge cases handled

Situation	Behaviour
File doesn't exist	Pass through
Binary file	Pass through
File uses spaces	Pass through (no warning needed)
Bash on non-file-edit command (go test, etc.)	Pass through
Write with matching indent style	Pass through
Read on non-tab file	Pass through

The hook fires on Read (PostToolUse), Bash, and Write (PreToolUse). A CLAUDE.md file is included in the release archive; placing it in your project root reinforces tab-awareness at session start.

Development

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