frisk-mcp
An MCP server for Frisk:
screen the counterparty of an x402 payment before an agent pays it.
It exposes one tool, screen_payment, which runs Frisk's deterministic checks —
address sanity, dynamic-payTo comparison, transport safety, and your own
spending policy — and returns allow / review / block with reasons.
Where this belongs, and where it does not
An MCP tool runs when a model decides to call it. A payment check that the model
can skip is a weaker guarantee than the same check on the code path that signs
the payment.
So:
- Use the library —
frisk-screen —
where the money actually moves. It is MIT, dependency-free, and runs locally.
- Use this server for inspection ("is this address safe to pay?"), and for
agents that cannot import a library.
Frisk is advisory in both cases: it returns a verdict and your code decides. It
never holds funds and cannot stop a payment by itself.
Install
In any MCP client's server configuration:
{
"mcpServers": {
"frisk": {
"command": "npx",
"args": ["-y", "frisk-mcp"]
}
}
}
No API key, no account, no network call: with no configuration the server
screens entirely on your machine.
Hosted mode (optional)
Set FRISK_API_KEY to have the same tool answered by the hosted service, which
adds reputation-graph signals and returns higher-confidence verdicts:
{
"mcpServers": {
"frisk": {
"command": "npx",
"args": ["-y", "frisk-mcp"],
"env": { "FRISK_API_KEY": "..." }
}
}
}
The hosted tier is in early access — email support@tryfrisk.dev. Everything
above works without it.
| variable | default | meaning |
|---|
FRISK_API_KEY | unset | Enables hosted screening. Unset means fully offline. |
FRISK_BASE_URL | https://api.tryfrisk.dev | Override the hosted endpoint. |
screen_payment
| argument | type | notes |
|---|
counterparty | string, required | The address the agent intends to pay. |
endpoint | string | URL that quoted the payment; checked for plaintext transport. |
amount | number | Amount about to be paid. |
asset | string | Asset symbol, e.g. USDC. |
observedPayTo | string | The payTo the endpoint actually returned. If it differs from counterparty, that is the dynamic-payTo swap. |
strictness | number 0–1 | 0 permissive, 1 paranoid. Default 0.3. |
maxPerCall | number | Spending ceiling for one call. |
allowedAssets | string[] | Assets the agent may pay in. |
Returns verdict, trustScore, confidence, reasons, policyHits,
source (lite or hosted), and allowed.
What it does not do
It does not detect Sybil clusters, and offline it has no view of an address's
history — lite screening always reports "low" confidence for that reason. It
also cannot repair the protocol underneath a payment: replay, settlement races,
and facilitator trust live in x402 itself, not in the request being signed.
Those limits are discussed in
Five ways an x402 payment can go wrong.
License
MIT