curl -fsSL https://agent-evidence.thx93.dev/buy.mjs -o buy.mjs
export X402_PRIVATE_KEY=0x...        # a wallet holding a little USDC on Base
node buy.mjs "Is Company X a manufacturer of centrifugal pumps?" \
    https://company.example/about https://company.example/products

Or, if you prefer npm:

npx @thx93/x402-evidence "your question" https://source.example

What you get back

Not a prose summary — a structured evidence package you can cite:

An explicit assessment: supported · contradicted · mixed · inconclusive
Per-source provenance: requested URL, final URL after redirects, HTTP status, retrieval timestamp
Short quoted excerpts, each tied to the source it came from
A SHA-256 of the normalised content, so you can prove nothing changed underneath you
Document metadata: title, publisher, canonical URL, language, publication/modified dates, JSON-LD, Open Graph
Honest limitations, including when the evidence is inconclusive

Why an agent would pay for this

Your agent can fetch a page. What it usually can't do reliably:

Fetch safely. Every URL is treated as hostile: private/loopback/link-local/cloud-metadata addresses, decimal-and-octal-encoded IP tricks, dangerous ports, and redirects into any of those are all refused. DNS is re-validated at connect time, which is what defeats DNS rebinding.
Get a citation, not an opinion. Every excerpt carries the URL it came from, when it was retrieved, and a content hash. "The model said so" is not evidence.
Compare sources. Two sources that disagree produce mixed. That is the interesting answer, and it is the one a single-page read cannot give you.
Stay cheap. Pulling five pages into context costs far more in tokens than $0.01, and burns context window you need elsewhere.
Skip the plumbing. Bounded concurrency, response-size caps, decompression-bomb defence, timeouts, a TTL'd cache, and structured errors are already handled.

Payment flow

This is x402: plain HTTP, settled in USDC on Base.

you  ──POST /v1/evidence────────▶  402 Payment Required  (+ PAYMENT-REQUIRED header: price, network, recipient)
you  ──pay USDC, retry with PAYMENT-SIGNATURE──▶  200 OK  (evidence)

This CLI does all of that for you. If you'd rather do it yourself, any x402 client works against the same endpoint.

Network: Base mainnet (eip155:8453)
Asset: USDC
Price: $0.01 per request
Recipient: published in the 402 response — the endpoint never sees your key

MCP (for agents)

The same capability is exposed as a remote MCP server, so an agent can call it as a tool:

https://agent-evidence.thx93.dev/mcp

Tools:

Tool	Cost	What it does
`research_evidence`	$0.01	Fetch public sources, return cited evidence and an assessment
`health`	free	Liveness and version

initialize and tools/list are free — an agent can discover the tools before deciding to pay for one. Only an actual research_evidence call is charged.

{
  "mcpServers": {
    "evidence": {
      "type": "streamable-http",
      "url": "https://agent-evidence.thx93.dev/mcp"
    }
  }
}

Verify the payment path without spending anything

node verify-payment-path.mjs

This signs a real EIP-3009 transferWithAuthorization with a throwaway unfunded wallet and asks the facilitator to verify it. Because the facilitator simulates the transfer against the live USDC contract, the rejection reason tells you how far the path got. Expected:

invalidReason: "invalid_exact_evm_insufficient_balance"
  → the plumbing is correct; the wallet merely has no USDC

Any other reason (format, scheme, network, signature) means a real defect. Exits non-zero only in that case, so it works as a pre-flight check.

Options

--url <endpoint>   override the endpoint
--max <usd>        refuse to pay more than this per call (default 0.10)
--json             print the raw response
--dry-run          show the quote without paying

Required environment

Variable	Meaning
`X402_PRIVATE_KEY`	A wallet private key holding a little USDC on Base

Read from the environment only. Never logged, stored, or transmitted anywhere except as a signed payment authorisation. Use a dedicated low-balance wallet.

Honest limitations

Assessment is deterministic lexical matching, not semantic reasoning. It never invents a fact and never emits a confidence score, and it returns inconclusive when the text does not clearly support or contradict. Read the basis and the excerpts; do not treat the status as ground truth.
You supply the URLs. There is no web search.
Excerpts are deliberately short. This is not a content-download service.
Not every URL is accessible — paywalls, logins and bot protection are not circumvented, by design.

Evidence, not truth.

FAQ

Do I need an API key? No. There is nothing to sign up for. The CLI pays per call in USDC on Base from the wallet you give it.

How much does a call cost? 0.01 USDC, and nothing when nothing is retrieved — if the service cannot deliver evidence, settlement is cancelled.

Where do I get a wallet? Any Base wallet works. The CLI reads the key from X402_PRIVATE_KEY or X402_PRIVATE_KEY_FILE and never sends it anywhere; only a signed payment authorisation leaves the process.

Can I see the output before paying? Yes — GET https://agent-evidence.thx93.dev/demo.json is one complete, unedited package from a real paid call.

How is this different from a search engine? It is not one. You supply the URLs; the CLI sends them and returns the passages that bear on your question, with the source URL, retrieval time and content hash.

What happens if a source is unreachable? It is reported per source and does not fail the whole request. If nothing at all is retrieved, you are not charged.

Does it work as an MCP tool? Yes — the same service is exposed over MCP at POST /mcp (tools research_evidence, sample, health).