About FabTally Guard
FabTally Guard is a paid, read-only MCP server for agents that need checks before package installs, x402 payments, JSON handling, or URL fetching. It exposes four stateless verification and data-preparation tools through stdio or hosted HTTP.
Key features
- 01Dependency risk checks
- 02x402 endpoint preflight
- 03JSON repair to schema
- 04Public URL to Markdown
Use cases
- 01Review a package before installation
- 02Check an x402 endpoint before payment
- 03Conform near-valid LLM JSON to a schema
- 04Prepare public-page text for RAG
MCP support
Exposes four paid tools to MCP clients over stdio or streamable HTTP. Calls can use an x402 payment payload; unpaid calls return a payment challenge.
Configuration
Remote servers need no local install. Pick your client, then copy the config or install in one click.
https://guard.fabtally.com/mcpclaude mcp add --transport http zvmzaretsky-fabtally-guard https://guard.fabtally.com/mcp{"mcpServers":{"zvmzaretsky-fabtally-guard":{"type":"http","url":"https://guard.fabtally.com/mcp"}}}Open in Cursor{"servers":{"zvmzaretsky-fabtally-guard":{"type":"http","url":"https://guard.fabtally.com/mcp"}}}Open in VS Code{"mcpServers":{"zvmzaretsky-fabtally-guard":{"type":"http","url":"https://guard.fabtally.com/mcp"}}}{"mcpServers":{"zvmzaretsky-fabtally-guard":{"serverUrl":"https://guard.fabtally.com/mcp"}}}Run commands in a terminal; paste JSON into the client’s MCP config and restart. Servers that need sign-in will prompt on first connect.
Tools
4| Parameter | Type | Required | Description |
|---|---|---|---|
| name | string | Yes | Package name, e.g. 'lodash', 'requests', 'serde'. |
| version | string | No | Specific version to check for CVEs (optional; defaults to latest). |
| ecosystem | enum | Yes | Package ecosystem: npm | pypi | crates.npm | pypi | crates |
| x_payment | string | No | x402 payment payload (base64) for this PAID check. If supplied it is forwarded as the X-PAYMENT header to settle the call and return the real result instead of a 402 challenge. Omit to get the price challenge first. |
Details
From the project READMEFabTally Guard — MCP server
De-risk-a-dollar verification checks an AI agent runs before a costly action. Fronts the Guard HTTP API at https://guard.fabtally.com. Holds no private key.
Tools (all paid; a call with no payment returns the decoded x402 402 challenge)
| Tool | Price | What it does |
|---|---|---|
deps_check | $0.003 | Vet a package before installing — OSV.dev CVEs, typosquat similarity, deprecation/yank, SPDX license, age/download signals + a plain-English risk verdict. Args: ecosystem (npm|pypi|crates), name, version?. |
x402_preflight | $0.002 | Verify another x402 endpoint before paying it — valid x402 v2 402 challenge? price/asset/network/payTo consistent with its /.well-known/x402? TLS/reachability/openapi? + the parsed price. Args: url. |
json_repair | $0.002 | Coerce near-miss LLM JSON to a JSON-Schema-conformant object (fences/commas/quotes/keys/literals/brackets, then type-coerce, defaults, drop extras) — or precise per-field errors. Args: json (string), schema. |
url_read | $0.004 | Fetch a public url → clean Markdown + token estimate for RAG. Respects robots.txt, public pages only, nothing stored. Args: url. |
Every tool also accepts an optional x_payment (base64 x402 payload) that is
forwarded as the X-PAYMENT header to settle the call and return the real result.
Humans can instead prepay by card and use an X-FabTally-Key credit key against
the HTTP API.
Transports
- stdio (portable):
npx fabtally-guard-mcp(bin:fabtally-guard-mcp) - streamable-http (hosted):
https://guard.fabtally.com/mcp
Config: FABTALLY_GUARD_BASE (default https://guard.fabtally.com).
Read-only, keyless, stateless, descriptive. Operated by Sunstone Soft (fabtally.com). Not a security guarantee.
Comments
New to MCP?
From what the protocol is to installing your first server, these answers cover most first questions.
An open protocol that defines how AI applications connect to external tools and data in a uniform way. Clients talk to the model; MCP servers provide tools, resources and prompt templates. They exchange standard messages, so one server can be reused by many clients.