vet402 for Hermes

Before your Hermes agent pays an x402 or MPP API, this plugin looks the URL up in vet402's public record of real purchases.

vet402 (https://vet402.com) buys from x402 and MPP sellers with its own USDC, checks each payment on chain, and publishes whether the seller delivered. The plugin reads that record and acts on it:

vet402's record	What happens
BLOCK	The tool call is stopped and no payment is made. The message gives the reasons and a link to the evidence.
WARN with evidence against the seller (vet402 paid and got nothing, its latest purchase failed, the answer didn't match the seller's own declaration)	Hermes asks you to approve the call. Approving it for the session or always applies to that URL only.
ALLOW	The call runs.
WARN only because vet402 hasn't bought there yet, no record, or vet402 unreachable	The call runs. Set VET402_UNKNOWN=approve to be asked instead.

Install

hermes plugins install vet402
hermes plugins enable vet402

No key and no wallet. Requires Hermes 0.19.0 or newer.

What it adds

• pre_tool_call hook. It runs before a paying tool: mpp_fetch from hermes-mpp by default. Add more tools with VET402_GUARD_TOOLS=mpp_fetch,other_tool. Any tool whose arguments carry a url works.
• vet402_check tool. The model can ask about any URL before it decides to pay. It returns the recommendation, the reason codes in vet402's words, how many times vet402 paid that endpoint and how often it delivered, and a link to the public page.

Limits

• hermes-mpp can also pay 402 challenges inside Hermes's own HTTPX traffic, outside any tool. Hooks don't see those payments. MPP_ALLOWED_ORIGINS is the control for them.
• vet402 only knows endpoints listed in public x402 and MPP discovery. For an unlisted URL the answer is "no record", which says nothing about the seller.
• Endpoints listed with a path parameter (for example /:chainId/quote) match only their listed path, so a call to /1/quote gets no record.
• Decisions follow vet402's published rules (https://vet402.com/observatory/methodology). The plugin keeps an answer for 5 minutes and vet402 may reuse one for 5 more, so an answer can be up to 10 minutes old.
• Without a key, vet402 answers 10 decisions per minute per IP. Past that, a lookup counts as unreachable.

Network and data

The plugin makes up to two HTTPS GET requests to vet402.com for each new URL: /api/v1/resolve?q=<url> and /api/v1/resources/<id>/decision?role=payer. It sends the URL your agent is about to pay, with any user:password, query string and fragment removed, and nothing else: no wallet address, no key, no request body. Answers stay in memory for 5 minutes. No telemetry, no files written, no shell commands, no background processes.

Settings

Variable	Default	Meaning
VET402_GUARD_TOOLS	mpp_fetch	Comma-separated tools to check before they run
VET402_UNKNOWN	allow	approve also asks you before paying a URL vet402 has no evidence about
VET402_API	https://vet402.com	API base
VET402_TIMEOUT_S	6	Request timeout in seconds

Tests

From the repository root:

python3 -m unittest discover -s tests

MIT license.