We Fixed Anthropic's Backspace Bug Before They Did

💥 The Problem

You're typing a prompt in Claude Code on Windows Terminal. You make a typo. You press Backspace.

The entire word vanishes. Not one letter. The whole word.

This started in Claude Code v2.1.113, which added Ctrl+Backspace as a word-delete shortcut on Windows. The feature works — but the key mappings are reversed.

🔬 The Investigation

We started where everyone starts: blaming the terminal. Windows Terminal uses ConPTY (a pseudo-terminal layer), and it has a history of mangling escape sequences. Seemed like the obvious culprit.

We tried everything at the terminal level:

🎯 The Breakthrough

We wrote a tiny Node.js script that captures raw bytes from stdin:

const fs = require("fs");
process.stdin.setRawMode(true);
process.stdin.resume();

let count = 0;
console.log("Press BACKSPACE, then CTRL+BACKSPACE:");

process.stdin.on("data", (data) => {
  count++;
  const label = count === 1 ? "BACKSPACE" : "CTRL+BACKSPACE";
  const bytes = [...data].map(b => "0x" + b.toString(16).padStart(2, "0"));
  console.log(`${label}: ${bytes.join(" ")}`);
  if (count >= 2) process.exit();
});

Opened a new Windows Terminal tab, ran it, and pressed both keys. The results:

BACKSPACE:      0x7f  (1 byte, decimal 127)
CTRL+BACKSPACE: 0x08  (1 byte, decimal 8)

Both correct. 0x7f is the standard Unix backspace. 0x08 is the standard Ctrl+Backspace. The terminal was doing its job perfectly.

We ran the test again for both keys. Here's what the terminal sends vs what Claude Code does with it:

The mappings are exactly reversed. Claude Code reads 0x7f and thinks "delete word." It reads 0x08 and thinks "delete character." Backwards.

🧩 Why It Only Hits Windows Terminal

Claude Code is built on Bun (not Node.js). Bun has a documented history of backspace bugs on Windows — specifically around the ENABLE_VIRTUAL_TERMINAL_INPUT console flag and how it interacts with ConPTY.

Terminals like mintty use a completely different PTY implementation (cygwin PTY), so the byte handling follows a different code path in Bun. Windows Terminal + ConPTY hits the broken one.

🔧 The Fix

Since we can't patch Claude Code's binary, we fix it at the terminal level. We tell Windows Terminal to swap the bytes before they reach Claude Code — counteracting the reversal.

Open your Windows Terminal settings JSON (press Ctrl+Shift+, inside Windows Terminal). Add these to the "actions" array:

{
    "command": { "action": "sendInput", "input": "\b" },
    "id": "User.sendInput.BackspaceAsSingleDelete",
    "keys": "backspace"
},
{
    "command": { "action": "sendInput", "input": "" },
    "id": "User.sendInput.CtrlBackspaceAsWordDelete",
    "keys": "ctrl+backspace"
}

Restart Windows Terminal. Backspace now deletes one character. Ctrl+Backspace deletes a word. The way it should be.

🤖 Let Claude Fix It For You

Paste this prompt into Claude Code and it will apply the fix automatically:

Backspace deletes entire words instead of single characters
in Windows Terminal. This is a known bug (#51841) where
Claude Code v2.1.113 reversed the byte mappings. Fix it by
adding two sendInput actions to my Windows Terminal
settings.json that swap the bytes: map Backspace to send \b
(0x08) and Ctrl+Backspace to send the DEL character 0x7f.
Open the settings file from within Windows Terminal using
Ctrl+Shift+, to find the correct path.

📋 The Timeline

Here's how it played out, start to finish:

💭 The Bigger Picture

This wasn't a complex fix. It was two lines of JSON. But finding those two lines meant ruling out every other possibility first — ConPTY passthrough, winpty wrappers, C# console flag overrides, Bun runtime patches.

We posted the full diagnostic and workaround to GitHub issue #51841. At the time of writing, it's the only comment with a working fix.

Visuals created with one-shot-scripts v3.7.0