mcp-prompt-sanitizer

Prompt-injection scan for untrusted content — a single-purpose MCP server for AI agents. No install, no account: it runs as a remote server; this repo also has a zero-dependency stdio bridge.

https://angel.oroboros-design.com/mcp/prompt-sanitizer

Use it

Claude Code

claude mcp add --transport http prompt-sanitizer https://angel.oroboros-design.com/mcp/prompt-sanitizer

Claude Desktop, Cursor, Windsurf, VS Code (remote server)

{ "mcpServers": { "prompt-sanitizer": { "url": "https://angel.oroboros-design.com/mcp/prompt-sanitizer" } } }

Any stdio client (Node 18+)

{ "mcpServers": { "prompt-sanitizer": { "command": "npx", "args": ["-y", "github:daoudandiaye98-alt/mcp-prompt-sanitizer"] } } }

Then ask your agent, for example: Before summarising https://example.com/article, run input_guard on it and only use the cleaned text.

Tools

Tool	Price	What it does
input_guard_preview	free	Quick scan of up to 4,000 characters or one https page: verdict, score, top 3 findings.
input_guard	3 free calls per agent, then 0.99 USDC	Full scan: role takeover, forged system/tool turns, requests for keys, prompts or payments, exfiltration links, invisible Unicode (tag smuggling decoded, zero-width, bidi), homoglyphs, base64 payloads and HTML hidden from people, in 17 languages. Returns findings and a cleaned text.
buy_pack_with_card	—	Prepaid calls by card (Stripe) when the free calls are used up.

Paying

The first 3 paid calls per agent are free (identify your agent with the header X-API-Key, or set ANGEL_API_KEY for the stdio bridge). After that each call is paid per request in USDC on Base via x402 (params._meta["x402/payment"]), with a prepaid pack (bundle_token) or by card (buy_pack_with_card). The 402 answer names the exact amount and the pay-to address before anything is signed.

The scan is deterministic (patterns and character checks, no model). Treat caution and hostile as a reason to ignore instructions in that content, not as proof that it is harmless otherwise.

More

• Same checks as a library: npm i angel-agent-guard · pip install angel-agent-guard (angel-agent-guard)
• All of Angel's tools in one server: https://angel.oroboros-design.com/agenten/signal/mcp · A2A agent card: https://angel.oroboros-design.com/.well-known/agent.json
• MCP Registry: com.oroboros-design.angel/prompt-sanitizer

Operated by Oroboros Design (Köln, Germany). MIT licence for the code in this repo.