GlyphGuard

Paste any text to find characters you can't see or that only look like what they seem: zero-width characters, bidi controls (Trojan Source), hidden Unicode tag text, mixed-script words and lookalike letters such as a Cyrillic "а" in "pаypal". Nothing you paste is stored.

Examples:

What it checks

Risk: high = bidi overrides/isolates, Unicode tag characters, mixed-script words or lookalikes inside them; medium = zero-width and other invisible characters, control characters, lookalike letters in Latin-looking words; low = variation selectors, unusual spaces, private-use characters; lone surrogates (malformed UTF-16) are medium. Joiners in legitimate context are info (type joiner_in_context, risk unchanged): ZWJ inside emoji ZWJ sequences, VS16 emoji presentation, ZWNJ/ZWJ between letters of joining scripts (Arabic, Persian) and after an Indic virama. ZWJ/ZWNJ anywhere else (for example inside an ASCII word) stay medium. clean keeps the in-context joiners by default (keep_joiners=true); strict=true removes them all. Offsets are UTF-16 code units (JavaScript string indexes). Up to 100 findings are listed; counts are always complete. Legitimate text in Cyrillic, Greek or CJK on its own is not flagged; only words that mix scripts are.

Emoji, Persian and Indic text are safe: zero-width joiners inside emoji like 🏳️‍🌈 and 👨‍👩‍👧‍👦, the Persian half-space in می‌خواهم and the Devanagari joiner in क्‍ष are shown as info and kept when cleaning. Add strict=true (or keep_joiners=false) to remove them anyway.

Text: up to 2000 UTF-16 code units, URL-encoded on GET (for example %E2%80%8B for a zero-width space). Names and targets: up to 128 characters each, 1-50 targets separated by | (or repeat target=). Booleans: true/false or 1/0.

JSON API

curl -s 'https://glyphguard.mike-tusa.workers.dev/api/scan?text=p%D0%B0ypal%E2%80%8B'
curl -s 'https://glyphguard.mike-tusa.workers.dev/api/compare?name=p%D0%B0ypal&targets=paypal|apple'

Routes: /api/scan, /api/clean and /api/compare (up to 50 protected names). No key needed: about 60 requests per minute per IP. OpenAPI 3.1 spec

For AI agents

GlyphGuard is also a remote Model Context Protocol (MCP) server with three read-only tools: scan_text, clean_text and compare_names. Agents can scan tool descriptions, retrieved pages or user input for hidden instructions before acting on them. Works with AI agents and assistants that can call an MCP server or a JSON API, for example Muse, Claude, ChatGPT or Cursor (descriptive only). Most MCP clients accept this config; some use a different format (for example, VS Code uses a servers key).

{ "mcpServers": { "glyphguard": { "type": "http", "url": "https://glyphguard.mike-tusa.workers.dev/mcp" } } }

Machine-readable docs: llms.txt · OpenAPI 3.1 spec · MCP server card. See Unicode TR #39. GlyphGuard is not affiliated with, endorsed by or sponsored by the Unicode Consortium, Meta, Anthropic, OpenAI or Anysphere. Results are a screening signal, not a security guarantee.

Privacy

Text you submit is processed in memory and discarded when the response is sent. It is never written to storage, logs or analytics, and GlyphGuard makes no network requests. Full privacy notice.