Agent Trust Oracle — x402 pay-per-call API

Pay-per-call ERC-8004 trust scores for AI agents, served over the x402 protocol on Base mainnet. An agent calls an endpoint, receives HTTP 402, pays USDC, and gets a machine-readable, ECDSA-signed trust score — no accounts, no API keys. Read-only on-chain analytics across 5 EVM chains (Ethereum, Base, BSC, Mantle, Polygon). Open-source, MIT.

Live: https://trust.nsgoods.org · Manifest: https://trust.nsgoods.org/.well-known/x402 · Methodology: https://trust.nsgoods.org/methodology

Why this API

• Signed & verifiable — every response carries signed_by + signature; recover against the published signer to prove the score is authentic and untampered, without paying.
• Tamper-evident — a public sha256 hash-chain (/provable/verify, /provable/head) is mirrored to GitHub (provable/scores_chain.jsonl), so every indexer run is committed on-chain-of-custody and anyone can audit history.
• Straight from canonical registries — scores are computed only from the canonical ERC-8004 Identity + Reputation registries; nothing is editorial or off-chain.
• No keys, no signup, free preview — try /agent-trust/preview for free, then pay per call in USDC on Base.

Endpoints

Paid endpoint settles in USDC on Base mainnet (eip155:8453). Default chain is ethereum, where ~99% of ERC-8004 agent activity currently lives. Identity is per-chain — agent IDs are not merged across chains.

Quickstart (call & pay in ~5 minutes)

Start free — no wallet, no funds:

curl -s https://trust.nsgoods.org/agent-trust/preview | jq

A runnable demo agent lives in the agent-starter-x402 template: it calls the FREE preview and prints the decoded x402 402 Payment Required challenge for the paid endpoint — no funds needed. Add a low-balance Base hot-wallet key and the same call auto-pays $0.005 USDC on Base for the signed score.

Verify a signed response

Every response carries signed_by + signature: an EIP-191 personal_sign over the JSON body (canonical json.dumps(sort_keys=True, separators=(",",":"))) before those two keys are added. Anyone can recover the signing address and confirm it equals the published signer 0x5e63d01d6A266BC17f577B80199a2a07B15053C7 — proving the score is authentic and untampered, without paying:

import json
from eth_account import Account
from eth_account.messages import encode_defunct

payload    = json.loads(response_body)
sig        = payload.pop("signature")
claimed    = payload.pop("signed_by")
canonical  = json.dumps(payload, sort_keys=True, separators=(",", ":"))
recovered  = Account.recover_message(encode_defunct(text=canonical), signature=sig)
assert recovered.lower() == claimed.lower()    # authentic & untampered

Run it against the FREE /agent-trust/preview endpoint — no funds required.

Tamper-evidence & sources

Each indexer run appends a sha256-chained snapshot to data/scores_chain.jsonl, mirrored to GitHub at provable/scores_chain.jsonl so every push is a public commit-of-record. Verify the chain live at /provable/verify. Scores derive only from the canonical read-only registries:

• IdentityRegistry 0x8004A169FB4a3325136EB29fA0ceB6D2e539a432
• ReputationRegistry 0x8004BAa17C55a88189AE136b182e5fdA19dE9b63
• Wired chain ids: 1 (ethereum), 8453 (base), 137 (polygon), 56 (bsc), 5000 (mantle)

Discovery

Listed on x402scan (as Agent Trust Oracle) and the x402 Bazaar (CDP Facilitator) — agents can find this API via Bazaar semantic search / merchant lookup. Settlement runs through the Coinbase CDP Facilitator.

Use with Claude Desktop / Cursor (MCP)

Wire the oracle into Claude Desktop, Cursor, or any MCP client as tools — no clone, no build. Add this to your client config and npx fetches and runs it:

{
  "mcpServers": {
    "agent-trust": {
      "command": "npx",
      "args": ["-y", "@nikosble1926/agent-trust-mcp"]
    }
  }
}

That gives you the free preview out of the box. To enable the paid tool, add a low-balance Base wallet key:

{
  "mcpServers": {
    "agent-trust": {
      "command": "npx",
      "args": ["-y", "@nikosble1926/agent-trust-mcp"],
      "env": {
        "EVM_PRIVATE_KEY": "0x<your-low-balance-base-wallet-private-key>"
      }
    }
  }
}

Restart the client, then ask: "Get an agent trust preview" (free) or "Get the trust score for agent 6976 on ethereum" (paid).

The EVM_PRIVATE_KEY is yours and stays local in your client config — it is never sent to the API. See mcp/ for full setup.

Run

pip install -r requirements.txt
cp .env.example .env       # then fill in real values
python3 indexer.py         # one-shot scan; idempotent
python3 app.py             # Flask dev server on :4023

Security

Only your public Base receiving address goes in .env on the service side. Never put a private key or seed phrase in this repo. For MCP paid mode, use a throwaway hot wallet holding only a little USDC.

Disclaimer

Read-only on-chain analytics, informational only. Not investment, employment, or counterparty advice — a score reflects observed ERC-8004 feedback and nothing more. Absence of evidence is not evidence of trustworthiness. Not a security audit of any agent.

License

MIT — © 2026 Nikoble1926.