ghostchar — invisible character guard 👻

Detect and decode invisible / dangerous Unicode characters right in your editor — the ones used for ASCII smuggling (hidden LLM instructions), Trojan Source attacks (CVE-2021-42574), and zero-width steganography.

Features

Highlights & diagnostics — flagged characters are decorated in the editor and reported as warnings in the Problems panel. Files are scanned when opened and on save.
Hover details — hover a flagged character to see its category, label, why it's dangerous, and — for tag / variation-selector / zero-width carriers — the decoded hidden payload inline.
Quick fix — decode the hidden payload when a decodable character (tag / variation-selector / zero-width) is flagged.
Paste guard — warns when pasted/inserted text contains invisible characters, with one-click Decode.
Decode hidden payloads — recover a hidden payload from the document or a selection; all schemes (tags / variation-selector / zero-width) are tried.
Encode / decode — round-trip text to and from invisible characters (for building detector tests and demos). Select text and right-click to Encode selection / Decode selection. Encoding offers three schemes: tags (printable ASCII only), variation-selector and zero-width (both carry any Unicode, e.g. Japanese or emoji).
Workspace scan — sweep the whole workspace on demand, or periodically in the background (off by default; configurable interval).

Detected categories

unicode-tags — Unicode Tag block (ASCII smuggling)
bidi-control — bidirectional overrides (Trojan Source)
zero-width — zero-width spaces / joiners / BOM
variation-selector — variation selectors (steganography)
invisible-operator — invisible math operators / soft hyphen
non-standard-space — look-alike whitespace

Every flagged character is highlighted in the editor and reported as a warning in the Problems panel — no severity tiers to configure.

Commands

Open the Command Palette and search for ghostchar:

Scan workspace for invisible characters
Decode hidden payload (all schemes)
Encode selection to invisible characters (choose scheme)
Decode selection

Settings

Setting	Default	Description
`ghostchar.enabledCategories`	all	Character categories to flag.
`ghostchar.pasteGuard`	`true`	Warn when pasted/inserted text contains invisible characters.
`ghostchar.scanOnSave`	`true`	Scan a file for invisible/dangerous characters when it is saved.
`ghostchar.automaticWorkspaceScan.enabled`	`false`	Periodically scan the whole workspace in the background.
`ghostchar.automaticWorkspaceScan.intervalMinutes`	`60`	Minutes between automatic workspace scans (when enabled).

Defensive & research tool. encode reproduces known smuggling techniques so detectors, tests, and demos have realistic payloads.

Educational Purpose

This tool is built for security research and education. Understanding these encoding techniques helps defenders build better detection systems. Use responsibly.

ghostchar