assay-oracle-mcp

assay-oracle-mcp

MCP server for Assay, the x402 service-quality oracle. Your agent asks Assay before paying any machine-payable (x402) service: is this thing actually any good?

Assay's answer is earned, not self-reported: it pays real USDC to probe x402 services several times a day, records whether payment settled (with the on-chain tx hash), whether the response matched the advertised schema, whether the data agreed with independent references, and how an LLM judged the response. Daily evidence digests are anchored to Bitcoin via OpenTimestamps, so history can't be quietly rewritten.

Install

Claude Code

claude mcp add assay -- npx -y assay-oracle-mcp

Claude Desktop / any MCP client — add to your MCP config:

{
  "mcpServers": {
    "assay": {
      "command": "npx",
      "args": ["-y", "assay-oracle-mcp"]
    }
  }
}

Requires Node 18+. No API key. (Not related to the npm package assay-mcp, a code-verification tool — this is the MCP server for the Assay x402 quality oracle.)

Tools

Tool	Cost	What it does
check_service	free	Quality tier (gold / ok / avoid / unrated) for an x402 resource URL, with a one-line verdict. Use before paying an unfamiliar endpoint.
get_score	free lookup¹	Full report: composite 0–100, component breakdown (settlement, schema, ground truth, LLM judge), 7-day trend, probe count.
top_services	free	Ranked list of the x402 services Assay actively probes, best first.

¹ GET /score is itself a paid x402 endpoint ($0.005 USDC on Base). The tool reports the 402 payment details when hit without payment; the free check_service tier verdict is sufficient for most pre-payment decisions.

Configuration

Env var	Default	Purpose
ASSAY_URL	https://assay.nominal-labs.com	Assay instance to query

How to read the tiers

• gold (composite ≥ 85) — consistently delivers what it charges for
• ok (≥ 60) — generally delivers, some failures
• avoid — frequently fails to deliver paid responses correctly
• unrated — under 20 probes so far; unproven, not bad
• a 404/unknown means Assay has no paid-probe evidence for that URL at all

Also see assay-x402-guard — a fetch wrapper that enforces these tiers automatically on every paid request your agent makes.

Full agent guide: https://assay.nominal-labs.com/SKILL.md · MIT © Nominal Labs